object attribute stuff

book/src/ch03/index.md

@@ -32,3 +32,21 @@ without trading away too much in terms of quality.
 To top it all off, we'll make a simple "memory game" sort of thing. There's some
 face down cards in a grid, you pick one to check, then you pick the other to
 check, and then if they match the pair disappears.
+
+## Drawing Priority
+
+Both backgrounds and objects can have "priority" values associated with them.
+TONC and GBATEK have _opposite_ ideas of what it means to have the "highest"
+priority. TONC goes by highest numerical value, and GBATEK goes by what's on the
+z-layer closest to the user. Let's list out the rules as clearly as we can:
+
+* Priority is always two bits, so 0 through 3.
+* Priority conceptually proceeds in drawing passes that count _down_, so any
+  priority 3 things can get covered up by priority 2 things. In truth there's
+  probably depth testing and buffering stuff going on so it's all one single
+  pass, but conceptually we will imagine it happening as all of the 3 elements,
+  then all of 2, and so on.
+* Objects always draw over top of backgrounds of equal priority.
+* Within things of the same type and priority, the lower numbered element "wins"
+  and gets its pixel drawn (bg0 is favored over bg1, obj0 is favored over obj1,
+  etc).

book/src/ch03/regular_backgrounds.md

@@ -122,10 +122,10 @@ GBA's CPU _can't do any of that_. On the GBA, there's a genuine speed difference
 between looping over indexes and then indexing each loop (slow) compared to
 using an iterator that just stores an internal pointer and does +1 offset per
 loop until it reaches the end (fast). The repeated indexing itself can by itself
-be an expensive step. If you've got a slice of data to process, be sure to go
+be an expensive step. If it's like a 3 element array it's no big deal, but if
-over it with `.iter()` and `.iter_mut()` if you can, instead of looping by
+you've got a big slice of data to process, be sure to go over it with `.iter()`
-index. This is Rust and all, so probably you were gonna do that anyway, but just
+and `.iter_mut()` if you can, instead of looping by index. This is Rust and all,
-a heads up.
+so probably you were gonna do that anyway, but just a heads up.
 
 ## Get your Tilemap ready
 
@@ -241,9 +241,7 @@ separate groups of related registers.
 Each of these are a read/write `u16` location. This is where we get to all of
 the important details that we've been putting off.
 
-* 2 bits for the priority of each background (0 being highest). If two
+* 2 bits for the priority.
-  backgrounds are set to the same priority the the lower numbered background
-  layer takes prescience.
 * 2 bits for "character base block", the charblock that all of the tile indexes
   for this background are offset from.
 * 1 bit for mosaic effect being enabled (we'll get to that below).

book/src/ch03/regular_objects.md

@@ -4,12 +4,387 @@ As with backgrounds, objects can be used in both an affine and non-affine way.
 For this section we'll focus on the non-affine elements, and then we'll do all
 the affine stuff in a later chapter.
 
-TODO: tio afero ke mi diris
-
 ## Objects vs Sprites
 
+As [TONC](https://www.coranac.com/tonc/text/regobj.htm) helpfully reminds us
+(and then proceeds to not follow its own advice), we should always try to think
+in terms of _objects_, not _sprites_. A sprite is a logical / software concern,
+perhaps a player concern, whereas an object is a hardware concern.
+
+What's more, a given sprite that the player sees might need more than one object
+to display. Objects must be either square or rectangular (so sprite bits that
+stick out probably call for a second object), and can only be from 8x8 to 64x64
+(so anything bigger has to be two objects lined up to appear as one).
+
+## General Object Info
+
+Unlike with backgrounds, you can enable the object layer in any video mode.
+There's space for 128 object definitions in OAM.
+
+The display gets a number of cycles per scanline to process objects: 1210 by
+default, but only 954 if you enable the "HBlank interval free" setting in the
+display control register. The [cycle cost per
+object](http://problemkaputt.de/gbatek.htm#lcdobjoverview) depends on the
+object's size and if it's using affine or regular mode, so enabling the HBlank
+interval free setting doesn't cut the number of objects displayable by an exact
+number of objects. The objects are processed in order of their definitions and
+if you run out of cycles then the rest just don't get shown. If there's a
+concern that you might run out of cycles you can place important objects (such
+as the player) at the start of the list and then less important animation
+objects later on.
+
 ## Ready the Palette
 
+Objects use the palette the same as the background does. The only difference is
+that the palette data for objects starts at `0x500_0200`.
+
+```rust
+pub const PALRAM_OBJECT_BASE: VolatilePtr<u16> = VolatilePtr(0x500_0200 as *mut u16);
+
+pub fn object_palette(slot: usize) -> u16 {
+  assert!(slot < 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).read() }
+}
+
+pub fn set_object_palette(slot: usize, color: u16) {
+  assert!(slot < 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).write(color) }
+}
+```
+
 ## Ready the Tiles
 
+Objects, as with backgrounds, are composed of 8x8 tiles, and if you want
+something bigger than 8x8 you have to use more than one tile put together.
+Object tiles go into the final two charblocks of VRAM (indexes 4 and 5). Because
+there's only two of them, they are sometimes called the lower block
+(`0x601_0000`) and the higher/upper block (`0x601_4000`).
+
+Tile indexes for sprites always offset from the base of the lower block, and
+they always go 32 bytes at a time, regardless of if the object is set for 4bpp
+or 8bpp. From this we can determine that there's 512 tile slots in each of the
+two object charblocks. However, in video modes 3, 4, and 5 the space for the
+background cuts into the lower charblock, so you can only safely use the upper
+charblock.
+
+With backgrounds you picked every single tile individually with a bunch of
+screen entry values. Objects don't do that at all. Instead you pick a base tile,
+size, and shape, then it figures out the rest from there. However, you may
+recall back with the display control register something about an "object memory
+1d" bit. This is where that comes into play.
+
+* If object memory is set to be 2d (the default) then each charblock is treated
+  as 32 tiles by 32 tiles square. Each object has a base tile and dimensions,
+  and that just extracts directly from the charblock picture as if you were
+  selecting an area. This mode probably makes for the easiest image editing.
+* If object memory is set to be 1d then the tiles are loaded sequentially from
+  the starting point, enough to fill in the object's dimensions. This most
+  probably makes it the easiest to program with about things, since programming
+  languages are pretty good at 1d things.
+
+I'm not sure I explained that well, here's a picture:
+
+![2d1d-diagram](obj_memory_2d1d.jpg)
+
+In 2d mode, a new row of tiles starts every 32 tile indexes.
+
+Of course, the mode that you actually end up using is not particularly
+important, since it should be the job of your image conversion routine to get
+everything all lined up and into place anyway.
+
 ## Set the Object Attributes
+
+The final step is to assign the correct attributes to an object. Each object has
+three `u16` values that make up its overall attributes.
+
+Before we go into the details, I want to remind you that the hardware will
+attempt to process every single object every single frame, and also that all of
+the GBA's memory is cleared to 0 at startup. Why do these two things matter
+right now? As you'll see in a second an "all zero" set of object attributes
+causes an 8x8 object to appear at 0,0 using object tile index 0. This is usually
+_not_ what you want your unused objects to do. When your game first starts you
+should take a moment to mark any objects you won't be using as objects to not
+render.
+
+### ObjectAttributes.attr0
+
+* 8 bits for row coordinate (marks the top of the sprite)
+* 2 bits for object rendering: 0 = Normal, 1 = Affine, 2 = Disabled, 3 = Affine with double rendering area
+* 2 bits for object mode: 0 = Normal, 1 = Alpha Blending, 2 = Object Window, 3 = Forbidden
+* 1 bit for mosaic enabled
+* 1 bit 8bpp color enabled
+* 2 bits for shape: 0 = Square, 1 = Horizontal, 2 = Vertical, 3 = Forbidden
+
+If an object is 128 pixels big at Y > 128 you'll get a strange looking result
+where it acts like Y > -128 and then displays partly off screen to the top.
+
+### ObjectAttributes.attr1
+
+* 9 bit for column coordinate (marks the left of the sprite)
+* Either:
+  * 3 empty bits, 1 bit for horizontal flip, 1 bit for vertical flip (non-affine)
+  * 5 bits for affine index (affine)
+* 2 bits for size.
+
+| Size | Square | Horizontal | Vertical|
+|:----:|:------:|:----------:|:-------:|
+| 0    | 8x8    | 16x8       | 8x16    |
+| 1    | 16x16  | 32x8       | 8x32    |
+| 2    | 32x32  | 32x16      | 16x32   |
+| 3    | 64x64  | 64x32      | 32x64   |
+
+### ObjectAttributes.attr2
+
+* 10 bits for the base tile index
+* 2 bits for priority
+* 4 bits for the palbank index (4bpp mode only, ignored in 8bpp)
+
+### ObjectAttributes summary
+
+So I said in the GBA memory mapping section that C people would tell you that
+the object attributes should look like this:
+
+```rust
+#[repr(C)]
+pub struct ObjectAttributes {
+  attr0: u16,
+  attr1: u16,
+  attr2: u16,
+  filler: i16,
+}
+```
+
+Except that:
+
+1) It's wasteful when we store object attributes on their own outside of OAM
+   (which we definitely might want to do).
+2) In Rust we can't access just one field through a volatile pointer (our
+   pointers aren't actually volatile to begin with, just the ops we do with them
+   are). We have to read or write the whole pointer's value at a time.
+   Similarly, we can't do things like `|=` and `&=` with volatile in Rust. So in
+   rust we can't have a volatile pointer to an ObjectAttributes and then write
+   to just the three "real" values and not touch the filler field. Having the
+   filler value in there just means we have to dance around it more, not less.
+3) We want to newtype this whole thing to prevent accidental invalid states from
+   being written into memory.
+
+So we will not be using that representation. At the same time we want to have no
+overhead, so we will stick to three `u16` values. We could newtype each
+individual field to be its own type (`ObjectAttributesAttr0` or something silly
+like that), since there aren't actual dependencies between two different fields
+such that a change in one can throw another into a forbidden state. The worst
+that can happen is if we disable or enable affine mode (`attr0`) it can change
+the meaning of `attr1`. The changed meaning isn't actually in invalid state
+though, so we _could_ make each field its own type if we wanted.
+
+However, when you think about it, I can't imagine a common situation where we do
+something like make an `attr0` value that we then want to save on its own and
+apply to several different `ObjectAttributes` that we make during a game. That
+just doesn't sound likely to me. So, we'll go the route where `ObjectAttributes`
+is just a big black box to the outside world and we don't need to think about
+the three fields internally as being separate.
+
+First we make it so that we can get and set object attributes from memory:
+
+```rust
+pub const OAM: usize = 0x700_0000;
+
+pub fn object_attributes(slot: usize) -> ObjectAttributes {
+  assert!(slot < 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::<u16>() * 4)) as *mut u16);
+  unsafe {
+    ObjectAttributes {
+      attr0: ptr.read(),
+      attr1: ptr.offset(1).read(),
+      attr2: ptr.offset(2).read(),
+    }
+  }
+}
+
+pub fn set_object_attributes(slot: usize, obj: ObjectAttributes) {
+  assert!(slot < 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::<u16>() * 4)) as *mut u16);
+  unsafe {
+    ptr.write(obj.attr0);
+    ptr.offset(1).write(obj.attr1);
+    ptr.offset(2).write(obj.attr2);
+  }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct ObjectAttributes {
+  attr0: u16,
+  attr1: u16,
+  attr2: u16,
+}
+```
+
+Then we add a billion methods to the `ObjectAttributes` type so that we can
+actually set all the different values that we want to set.
+
+This code block is the last thing on this page so if you don't wanna scroll past
+the whole thing you can just go to the next page.
+
+```rust
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectRenderMode {
+  Normal,
+  Affine,
+  Disabled,
+  DoubleAreaAffine,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectMode {
+  Normal,
+  AlphaBlending,
+  ObjectWindow,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectShape {
+  Square,
+  Horizontal,
+  Vertical,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectOrientation {
+  Normal,
+  HFlip,
+  VFlip,
+  BothFlip,
+  Affine(u8),
+}
+
+impl ObjectAttributes {
+  pub fn row(&self) -> u16 {
+    self.attr0 & 0b1111_1111
+  }
+  pub fn column(&self) -> u16 {
+    self.attr1 & 0b1_1111_1111
+  }
+  pub fn rendering(&self) -> ObjectRenderMode {
+    match (self.attr0 >> 8) & 0b11 {
+      0 => ObjectRenderMode::Normal,
+      1 => ObjectRenderMode::Affine,
+      2 => ObjectRenderMode::Disabled,
+      3 => ObjectRenderMode::DoubleAreaAffine,
+      _ => unimplemented!(),
+    }
+  }
+  pub fn mode(&self) -> ObjectMode {
+    match (self.attr0 >> 0xA) & 0b11 {
+      0 => ObjectMode::Normal,
+      1 => ObjectMode::AlphaBlending,
+      2 => ObjectMode::ObjectWindow,
+      _ => unimplemented!(),
+    }
+  }
+  pub fn mosaic(&self) -> bool {
+    ((self.attr0 << 3) as i16) < 0
+  }
+  pub fn two_fifty_six_colors(&self) -> bool {
+    ((self.attr0 << 2) as i16) < 0
+  }
+  pub fn shape(&self) -> ObjectShape {
+    match (self.attr0 >> 0xE) & 0b11 {
+      0 => ObjectShape::Square,
+      1 => ObjectShape::Horizontal,
+      2 => ObjectShape::Vertical,
+      _ => unimplemented!(),
+    }
+  }
+  pub fn orientation(&self) -> ObjectOrientation {
+    if (self.attr0 >> 8) & 1 > 0 {
+      ObjectOrientation::Affine((self.attr1 >> 9) as u8 & 0b1_1111)
+    } else {
+      match (self.attr1 >> 0xC) & 0b11 {
+        0 => ObjectOrientation::Normal,
+        1 => ObjectOrientation::HFlip,
+        2 => ObjectOrientation::VFlip,
+        3 => ObjectOrientation::BothFlip,
+      }
+    }
+  }
+  pub fn size(&self) -> u16 {
+    self.attr1 >> 0xE
+  }
+  pub fn tile_index(&self) -> u16 {
+    self.attr2 & 0b11_1111_1111
+  }
+  pub fn priority(&self) -> u16 {
+    self.attr2 >> 0xA
+  }
+  pub fn palbank(&self) -> u16 {
+    self.attr2 >> 0xC
+  }
+  //
+  pub fn set_row(&mut self, row: u16) {
+    self.attr0 &= !0b1111_1111;
+    self.attr0 |= row & 0b1111_1111;
+  }
+  pub fn set_column(&mut self, col: u16) {
+    self.attr1 &= !0b1_1111_1111;
+    self.attr2 |= col & 0b1_1111_1111;
+  }
+  pub fn set_rendering(&mut self, rendering: ObjectRenderMode) {
+    const RENDERING_MASK: u16 = 0b11 << 8;
+    self.attr0 &= !RENDERING_MASK;
+    self.attr0 |= (rendering as u16) << 8;
+  }
+  pub fn set_mode(&mut self, mode: ObjectMode) {
+    const MODE_MASK: u16 = 0b11 << 0xA;
+    self.attr0 &= MODE_MASK;
+    self.attr0 |= (mode as u16) << 0xA;
+  }
+  pub fn set_mosaic(&mut self, bit: bool) {
+    const MOSAIC_BIT: u16 = 1 << 0xC;
+    if bit {
+      self.attr0 |= MOSAIC_BIT
+    } else {
+      self.attr0 &= !MOSAIC_BIT
+    }
+  }
+  pub fn set_two_fifty_six_colors(&mut self, bit: bool) {
+    const COLOR_MODE_BIT: u16 = 1 << 0xD;
+    if bit {
+      self.attr0 |= COLOR_MODE_BIT
+    } else {
+      self.attr0 &= !COLOR_MODE_BIT
+    }
+  }
+  pub fn set_shape(&mut self, shape: ObjectShape) {
+    self.attr0 &= 0b0011_1111_1111_1111;
+    self.attr0 |= (shape as u16) << 0xE;
+  }
+  pub fn set_orientation(&mut self, orientation: ObjectOrientation) {
+    const AFFINE_INDEX_MASK: u16 = 0b1_1111 << 9;
+    self.attr1 &= !AFFINE_INDEX_MASK;
+    let bits = match orientation {
+      ObjectOrientation::Affine(index) => (index as u16) << 9,
+      ObjectOrientation::Normal => 0,
+      ObjectOrientation::HFlip => 1 << 0xC,
+      ObjectOrientation::VFlip => 1 << 0xD,
+      ObjectOrientation::BothFlip => 0b11 << 0xC,
+    };
+    self.attr1 |= bits;
+  }
+  pub fn set_size(&mut self, size: u16) {
+    self.attr1 &= 0b0011_1111_1111_1111;
+    self.attr1 |= size << 14;
+  }
+  pub fn set_tile_index(&mut self, index: u16) {
+    self.attr2 &= !0b11_1111_1111;
+    self.attr2 |= 0b11_1111_1111 & index;
+  }
+  pub fn set_priority(&mut self, priority: u16) {
+    self.attr2 &= !0b0000_1100_0000_0000;
+    self.attr2 |= (priority & 0b11) << 0xA;
+  }
+  pub fn set_palbank(&mut self, palbank: u16) {
+    self.attr2 &= !0b1111_0000_0000_0000;
+    self.attr2 |= (palbank & 0b1111) << 0xC;
+  }
+}
+```

docs/ch00/index.html

@@ -72,7 +72,7 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html" class="active"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html" class="active"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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docs/ch01/hello1.html

@@ -72,7 +72,7 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html" class="active"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html" class="active"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html" class="active"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html" class="active"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html" class="active"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html" class="active"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html" class="active"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html" class="active"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html" class="active"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html" class="active"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html" class="active"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html" class="active"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html" class="active"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html" class="active"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html" class="active"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html" class="active"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html" class="active"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html" class="active"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html" class="active"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html" class="active"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html" class="active"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html" class="active"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
         </nav>
 
         <div id="page-wrapper" class="page-wrapper">

docs/ch03/gba_memory_mapping.html

@@ -72,7 +72,7 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html" class="active"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html" class="active"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
         </nav>
 
         <div id="page-wrapper" class="page-wrapper">
@@ -225,6 +225,20 @@ and then a <em>separate</em> setting outside of the graphical data determines wh
 palbank is to be used for that background or object (the screen entry data for
 backgrounds, and the object attributes for objects).</li>
 </ul>
+<a class="header" href="#transparency" id="transparency"><h3>Transparency</h3></a>
+<p>When a pixel within a background or object specifies index 0 as its palette
+entry it is treated as a transparent pixel. This means that in 8bpp mode there's
+only 255 actual color options (0 being transparent), and in 4bpp mode there's
+only 15 actual color options available within each palbank (the 0th entry of
+<em>each</em> palbank is transparent).</p>
+<p>Individual backgrounds, and individual objects, each determine if they're 4bpp
+or 8bpp separately, so a given overall palette slot might map to a used color in
+8bpp and an unused/transparent color in 4bpp. If you're a palette wizard.</p>
+<p>Palette slot 0 of the overall background palette is used to determine the
+&quot;backdrop&quot; color. That's the color you see if no background or object ends up
+being rendered within a given pixel.</p>
+<p>Since display mode 3 and display mode 5 don't use the palette, they cannot
+benefit from transparency.</p>
 <a class="header" href="#video-ram--vram" id="video-ram--vram"><h2>Video RAM / VRAM</h2></a>
 <ul>
 <li><code>0x6000000</code> to <code>0x6017FFF</code> (96k)</li>

docs/ch03/gba_rng.html

@@ -72,7 +72,7 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html" class="active"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html" class="active"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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@@ -144,7 +144,7 @@
                     <nav class="nav-wrapper" aria-label="Page navigation">
                         <!-- Mobile navigation buttons -->
                         
-                            <a rel="prev" href="../ch03/object_basics.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
+                            <a rel="prev" href="../ch03/regular_objects.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
                                 <i class="fa fa-angle-left"></i>
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@@ -162,7 +162,7 @@
 
             <nav class="nav-wide-wrapper" aria-label="Page navigation">
                 
-                    <a href="../ch03/object_basics.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
+                    <a href="../ch03/regular_objects.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
                         <i class="fa fa-angle-left"></i>
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@@ -72,7 +72,7 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html" class="active"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html" class="active"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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@@ -165,6 +165,23 @@ without trading away too much in terms of quality.</p>
 <p>To top it all off, we'll make a simple &quot;memory game&quot; sort of thing. There's some
 face down cards in a grid, you pick one to check, then you pick the other to
 check, and then if they match the pair disappears.</p>
+<a class="header" href="#drawing-priority" id="drawing-priority"><h2>Drawing Priority</h2></a>
+<p>Both backgrounds and objects can have &quot;priority&quot; values associated with them.
+TONC and GBATEK have <em>opposite</em> ideas of what it means to have the &quot;highest&quot;
+priority. TONC goes by highest numerical value, and GBATEK goes by what's on the
+z-layer closest to the user. Let's list out the rules as clearly as we can:</p>
+<ul>
+<li>Priority is always two bits, so 0 through 3.</li>
+<li>Priority conceptually proceeds in drawing passes that count <em>down</em>, so any
+priority 3 things can get covered up by priority 2 things. In truth there's
+probably depth testing and buffering stuff going on so it's all one single
+pass, but conceptually we will imagine it happening as all of the 3 elements,
+then all of 2, and so on.</li>
+<li>Objects always draw over top of backgrounds of equal priority.</li>
+<li>Within things of the same type and priority, the lower numbered element &quot;wins&quot;
+and gets its pixel drawn (bg0 is favored over bg1, obj0 is favored over obj1,
+etc).</li>
+</ul>
 
                     </main>
 

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@@ -72,7 +72,7 @@
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@@ -136,8 +136,291 @@
 
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                     <main>
-                        <a class="header" href="#tiled-backgrounds" id="tiled-backgrounds"><h1>Tiled Backgrounds</h1></a>
+                        <a class="header" href="#regular-backgrounds" id="regular-backgrounds"><h1>Regular Backgrounds</h1></a>
-<p>TODO</p>
+<p>So, backgrounds, they're cool. Why do we call the ones here &quot;regular&quot;
+backgrounds? Because there's also &quot;affine&quot; backgrounds. However, affine math
+stuff adds a complication, so for now we'll just work with regular backgrounds.
+The non-affine backgrounds are sometimes called &quot;text mode&quot; backgrounds by other
+guides.</p>
+<p>To get your background image working you generally need to perform all of the
+following steps, though I suppose the exact ordering is up to you.</p>
+<a class="header" href="#tiled-video-modes" id="tiled-video-modes"><h2>Tiled Video Modes</h2></a>
+<p>When you want regular tiled display, you must use video mode 0 or 1.</p>
+<ul>
+<li>Mode 0 allows for using all four BG layers (0 through 3) as regular
+backgrounds.</li>
+<li>Mode 1 allows for using BG0 and BG1 as regular backgrounds, BG2 as an affine
+background, and BG3 not at all.</li>
+<li>Mode 2 allows for BG2 and BG3 to be used as affine backgrounds, while BG0 and
+BG1 cannot be used at all.</li>
+</ul>
+<p>We will not cover affine backgrounds in this chapter, so we will naturally be
+using video mode 0.</p>
+<p>Also, note that you have to enable each background layer that you want to use
+within the display control register.</p>
+<a class="header" href="#get-your-palette-ready" id="get-your-palette-ready"><h2>Get Your Palette Ready</h2></a>
+<p>Background palette starts at <code>0x5000000</code> and is 256 <code>u16</code> values long. It'd
+potentially be possible declare a static array starting at a fixed address and
+use a linker script to make sure that it ends up at the right spot in the final
+program, but since we have to use volatile reads and writes with PALRAM anyway,
+we'll just reuse our <code>VolatilePtr</code> type. Something like this:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub const PALRAM_BG_BASE: VolatilePtr&lt;u16&gt; = VolatilePtr(0x500_0000 as *mut u16);
+
+pub fn bg_palette(slot: usize) -&gt; u16 {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_BG_BASE.offset(slot as isize).read() }
+}
+
+pub fn set_bg_palette(slot: usize, color: u16) {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_BG_BASE.offset(slot as isize).write(color) }
+}
+#}</code></pre></pre>
+<p>As we discussed with the tile color depths, the palette can be utilized as a
+single block of palette values (<code>[u16; 256]</code>) or as 16 palbanks of 16 palette
+values each (<code>[[u16;16]; 16]</code>). This setting is assigned per background layer
+via IO register.</p>
+<a class="header" href="#get-your-tiles-ready" id="get-your-tiles-ready"><h2>Get Your Tiles Ready</h2></a>
+<p>Tile data is placed into charblocks. A charblock is always 16kb, so depending on
+color depth it will have either 256 or 512 tiles within that charblock.
+Charblocks 0, 1, 2, and 3 are all for background tiles. That's a maximum of 2048
+tiles for backgrounds, but as you'll see in a moment a particular tilemap entry
+can't even index that high. Instead, each background layer is assigned a
+&quot;character base block&quot;, and then tilemap entries index relative to the character
+base block of that background layer.</p>
+<p>Now, if you want to move in a lot of tile data you'll probably want to use a DMA
+routine, or at least write a function like memcopy32 for fast <code>u32</code> copying from
+ROM into VRAM. However, for now, and because we're being very explicit since
+this is our first time doing it, we'll write it as functions for individual tile
+reads and writes.</p>
+<p>The math works like indexing a pointer, except that we have two sizes we need to
+go by. First you take the base address for VRAM (<code>0x600_0000</code>), then add the
+size of a charblock (16kb) times the charblock you want to place the tile
+within, and then you add the index of the tile slot you're placing it into times
+the size of that type of tile. Like this:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub fn bg_tile_4pp(base_block: usize, tile_index: usize) -&gt; Tile4bpp {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 512);
+  let address = VRAM + size_of::&lt;Charblock4bpp&gt;() * base_block + size_of::&lt;Tile4bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile4bpp).read() }
+}
+
+pub fn set_bg_tile_4pp(base_block: usize, tile_index: usize, tile: Tile4bpp) {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 512);
+  let address = VRAM + size_of::&lt;Charblock4bpp&gt;() * base_block + size_of::&lt;Tile4bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile4bpp).write(tile) }
+}
+
+pub fn bg_tile_8pp(base_block: usize, tile_index: usize) -&gt; Tile8bpp {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 256);
+  let address = VRAM + size_of::&lt;Charblock8bpp&gt;() * base_block + size_of::&lt;Tile8bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile8bpp).read() }
+}
+
+pub fn set_bg_tile_8pp(base_block: usize, tile_index: usize, tile: Tile8bpp) {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 256);
+  let address = VRAM + size_of::&lt;Charblock8bpp&gt;() * base_block + size_of::&lt;Tile8bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile8bpp).write(tile) }
+}
+#}</code></pre></pre>
+<p>For bulk operations, you'd do the exact same math to get your base destination
+pointer, and then you'd get the base source pointer for the tile you're copying
+out of ROM, and then you'd do the bulk copy for the correct number of <code>u32</code>
+values that you're trying to move (8 per tile moved for 4bpp, or 16 per tile
+moved for 8bpp).</p>
+<p><strong>GBA Limitation Note:</strong> on a modern PC (eg: <code>x86</code> or <code>x86_64</code>) you're probably
+used to index based loops and iterator based loops being the same speed. The CPU
+has the ability to do a &quot;fused multiply add&quot;, so the base address of the array
+plus desired index * size per element is a single CPU operation to compute. It's
+slightly more complicated if there's arrays within arrays like there are here,
+but with normal arrays it's basically the same speed to index per loop cycle as
+it is to take a base address and then add +1 offset per loop cycle. However, the
+GBA's CPU <em>can't do any of that</em>. On the GBA, there's a genuine speed difference
+between looping over indexes and then indexing each loop (slow) compared to
+using an iterator that just stores an internal pointer and does +1 offset per
+loop until it reaches the end (fast). The repeated indexing itself can by itself
+be an expensive step. If it's like a 3 element array it's no big deal, but if
+you've got a big slice of data to process, be sure to go over it with <code>.iter()</code>
+and <code>.iter_mut()</code> if you can, instead of looping by index. This is Rust and all,
+so probably you were gonna do that anyway, but just a heads up.</p>
+<a class="header" href="#get-your-tilemap-ready" id="get-your-tilemap-ready"><h2>Get your Tilemap ready</h2></a>
+<p>I believe that at one point I alluded to a tilemap existing. Well, just as the
+tiles are arranged into charblocks, the data describing what tile to show in
+what location is arranged into a thing called a <strong>screenblock</strong>.</p>
+<p>A screenblock is placed into VRAM the same as the tile data charblocks. Starting
+at the base of VRAM (<code>0x600_0000</code>) there are 32 slots for the screenblock array.
+Each screenblock is 2048 bytes (<code>0x800</code>). Naturally, if our tiles are using up
+charblock space within VRAM and our tilemaps are using up screenblock space
+within the same VRAM... well it would just be a <em>disaster</em> if they ran in to
+each other. Once again, it's up to you as the programmer to determine how much
+space you want to devote to each thing. Each complete charblock uses up 8
+screenblocks worth of space, but you don't have to fill a complete charblock
+with tiles, so you can be very fiddly with how you split the memory.</p>
+<p>Each screenblock is composed of a series of <em>screenblock entry</em> values, which
+describe what tile index to use and if the tile should be flipped and what
+palbank it should use (if any). Because both regular backgrounds and affine
+backgrounds are composed of screenblocks with entries, and because the affine
+background has a smaller format for screenblock entries, we'll name
+appropriately.</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+#[derive(Clone, Copy)]
+#[repr(transparent)]
+pub struct RegularScreenblock {
+  data: [RegularScreenblockEntry; 32 * 32],
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+#[repr(transparent)]
+pub struct RegularScreenblockEntry(u16);
+#}</code></pre></pre>
+<p>So, with one entry per tile, a single screenblock allows for 32x32 tiles worth of
+background.</p>
+<p>The format of a regular screenblock entry is quite simple compared to some of
+the IO register stuff:</p>
+<ul>
+<li>10 bits for tile index (base off of the character base block of the background)</li>
+<li>1 bit for horizontal flip</li>
+<li>1 bit for vertical flip</li>
+<li>4 bits for picking which palbank to use (if 4bpp, otherwise it's ignored)</li>
+</ul>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+impl RegularScreenblockEntry {
+  pub fn tile_id(self) -&gt; u16 {
+    self.0 &amp; 0b11_1111_1111
+  }
+  pub fn set_tile_id(&amp;mut self, id: u16) {
+    self.0 &amp;= !0b11_1111_1111;
+    self.0 |= id;
+  }
+  pub fn horizontal_flip(self) -&gt; bool {
+    (self.0 &amp; (1 &lt;&lt; 0xA)) &gt; 0
+  }
+  pub fn set_horizontal_flip(&amp;mut self, bit: bool) {
+    if bit {
+      self.0 |= 1 &lt;&lt; 0xA;
+    } else {
+      self.0 &amp;= !(1 &lt;&lt; 0xA);
+    }
+  }
+  pub fn vertical_flip(self) -&gt; bool {
+    (self.0 &amp; (1 &lt;&lt; 0xB)) &gt; 0
+  }
+  pub fn set_vertical_flip(&amp;mut self, bit: bool) {
+    if bit {
+      self.0 |= 1 &lt;&lt; 0xB;
+    } else {
+      self.0 &amp;= !(1 &lt;&lt; 0xB);
+    }
+  }
+  pub fn palbank_index(self) -&gt; u16 {
+    self.0 &gt;&gt; 12
+  }
+  pub fn set_palbank_index(&amp;mut self, palbank_index: u16) {
+    self.0 &amp;= 0b1111_1111_1111;
+    self.0 |= palbank_index;
+  }
+}
+#}</code></pre></pre>
+<p>Now, at either 256 or 512 tiles per charblock, you might be thinking that with a
+10 bit index you can index past the end of one charblock and into the next.
+You'd be right, mostly.</p>
+<p>As long as you stay within the background memory region for charblocks (that is,
+0 through 3), then it all works out. However, if you try to get the background
+rendering to reach outside of the background charblocks you'll get an
+implementation defined result. It's not the dreaded &quot;undefined behavior&quot; we're
+often worried about in programming, but the results <em>are</em> determined by what
+you're running the game on. With GBA hardware you get a bizarre result
+(basically another way to put garbage on the screen). With a DS it acts as if
+the tiles were all 0s. If you use an emulator it might or might not allow for
+you to do this, it's up to the emulator writers.</p>
+<a class="header" href="#set-your-io-registers" id="set-your-io-registers"><h2>Set Your IO Registers</h2></a>
+<p>Instead of being just a single IO register to learn about this time, there's two
+separate groups of related registers.</p>
+<a class="header" href="#background-control" id="background-control"><h3>Background Control</h3></a>
+<ul>
+<li>BG0CNT (<code>0x400_0008</code>): BG0 Control</li>
+<li>BG1CNT (<code>0x400_000A</code>): BG1 Control</li>
+<li>BG2CNT (<code>0x400_000C</code>): BG2 Control</li>
+<li>BG3CNT (<code>0x400_000E</code>): BG3 Control</li>
+</ul>
+<p>Each of these are a read/write <code>u16</code> location. This is where we get to all of
+the important details that we've been putting off.</p>
+<ul>
+<li>2 bits for the priority.</li>
+<li>2 bits for &quot;character base block&quot;, the charblock that all of the tile indexes
+for this background are offset from.</li>
+<li>1 bit for mosaic effect being enabled (we'll get to that below).</li>
+<li>1 bit to enable 8bpp, otherwise 4bpp is used.</li>
+<li>5 bits to pick the &quot;screen base block&quot;, the screen block that serves as the
+<em>base</em> value for this background.</li>
+<li>1 bit that is <em>not</em> used in regular mode, but in affine mode it can be enabled
+to cause the affine background to wrap around at the edges.</li>
+<li>2 bits for the background size.</li>
+</ul>
+<p>The size works a little funny. When size is 0 only the base screen block is
+used. If size is 1 or 2 then the base screenblock and the following screenblock
+are placed next to each other (horizontally for 1, vertically for 2). If the
+size is 3 then the base screenblock and the following three screenblocks are
+arranged into a 2x2 grid of screenblocks.</p>
+<a class="header" href="#background-offset" id="background-offset"><h3>Background Offset</h3></a>
+<ul>
+<li>BG0HOFS (<code>0x400_0010</code>): BG0 X-Offset</li>
+<li>BG0VOFS (<code>0x400_0012</code>): BG0 Y-Offset</li>
+<li>BG1HOFS (<code>0x400_0014</code>): BG1 X-Offset</li>
+<li>BG1VOFS (<code>0x400_0016</code>): BG1 Y-Offset</li>
+<li>BG2HOFS (<code>0x400_0018</code>): BG2 X-Offset</li>
+<li>BG2VOFS (<code>0x400_001A</code>): BG2 Y-Offset</li>
+<li>BG3HOFS (<code>0x400_001C</code>): BG3 X-Offset</li>
+<li>BG3VOFS (<code>0x400_001E</code>): BG3 Y-Offset</li>
+</ul>
+<p>Each of these are a <em>write only</em> <code>u16</code> location. Bits 0 through 8 are used, so
+the offsets can be 0 through 511. They also only apply in regular backgrounds.
+If a background is in an affine state then you'll use different IO registers to
+control it (discussed in a later chapter).</p>
+<p>The offset that you assign determines the pixel offset of the display area
+relative to the start of the background scene, as if the screen was a camera
+looking at the scene. In other words, as a BG X offset value increases, you can
+think of it as the camera moving to the right, or as that background moving to
+the left. Like when mario walks toward the goal. Similarly, when a BG Y offset
+increases the camera is moving down, or the background is moving up, like when
+mario falls down from a high platform.</p>
+<p>Depending on how much the background is scrolled and the size of the background,
+it will loop.</p>
+<a class="header" href="#mosaic" id="mosaic"><h2>Mosaic</h2></a>
+<p>As a special effect, you can apply mosaic to backgrounds and objects. It's just
+a single flag for each background, so all backgrounds will use the same mosaic
+settings when they have it enabled. What it actually does is split the normal
+image into &quot;blocks&quot; and then each block gets the color of the top left pixel of
+that block. This is the effect you see when link hits an electric foe with his
+sword and the whole screen &quot;buzzes&quot; at you.</p>
+<p>The mosaic control is a <em>write only</em> <code>u16</code> IO register at <code>0x400_004C</code>.</p>
+<p>There's 4 bits each for:</p>
+<ul>
+<li>Horizontal BG stretch</li>
+<li>Vertical BG stretch</li>
+<li>Horizontal object stretch</li>
+<li>Vertical object stretch</li>
+</ul>
+<p>The inputs should be 1 <em>less</em> than the desired block size. So if you set a
+stretch value of 5 then pixels 0-5 would be part of the first block (6 pixels),
+then 6-11 is the next block (another 6 pixels) and so on.</p>
+<p>If you need to make a pixel other than the top left part of each block the one
+that determines the mosaic color you can carefully offset the background or
+image by a tiny bit, but of course that makes every mosaic block change its
+target pixel. You can't change the target pixel on a block by block basis.</p>
 
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+                        <a class="header" href="#regular-objects" id="regular-objects"><h1>Regular Objects</h1></a>
+<p>As with backgrounds, objects can be used in both an affine and non-affine way.
+For this section we'll focus on the non-affine elements, and then we'll do all
+the affine stuff in a later chapter.</p>
+<a class="header" href="#objects-vs-sprites" id="objects-vs-sprites"><h2>Objects vs Sprites</h2></a>
+<p>As <a href="https://www.coranac.com/tonc/text/regobj.htm">TONC</a> helpfully reminds us
+(and then proceeds to not follow its own advice), we should always try to think
+in terms of <em>objects</em>, not <em>sprites</em>. A sprite is a logical / software concern,
+perhaps a player concern, whereas an object is a hardware concern.</p>
+<p>What's more, a given sprite that the player sees might need more than one object
+to display. Objects must be either square or rectangular (so sprite bits that
+stick out probably call for a second object), and can only be from 8x8 to 64x64
+(so anything bigger has to be two objects lined up to appear as one).</p>
+<a class="header" href="#general-object-info" id="general-object-info"><h2>General Object Info</h2></a>
+<p>Unlike with backgrounds, you can enable the object layer in any video mode.
+There's space for 128 object definitions in OAM.</p>
+<p>The display gets a number of cycles per scanline to process objects: 1210 by
+default, but only 954 if you enable the &quot;HBlank interval free&quot; setting in the
+display control register. The <a href="http://problemkaputt.de/gbatek.htm#lcdobjoverview">cycle cost per
+object</a> depends on the
+object's size and if it's using affine or regular mode, so enabling the HBlank
+interval free setting doesn't cut the number of objects displayable by an exact
+number of objects. The objects are processed in order of their definitions and
+if you run out of cycles then the rest just don't get shown. If there's a
+concern that you might run out of cycles you can place important objects (such
+as the player) at the start of the list and then less important animation
+objects later on.</p>
+<a class="header" href="#ready-the-palette" id="ready-the-palette"><h2>Ready the Palette</h2></a>
+<p>Objects use the palette the same as the background does. The only difference is
+that the palette data for objects starts at <code>0x500_0200</code>.</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub const PALRAM_OBJECT_BASE: VolatilePtr&lt;u16&gt; = VolatilePtr(0x500_0200 as *mut u16);
+
+pub fn object_palette(slot: usize) -&gt; u16 {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).read() }
+}
+
+pub fn set_object_palette(slot: usize, color: u16) {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).write(color) }
+}
+#}</code></pre></pre>
+<a class="header" href="#ready-the-tiles" id="ready-the-tiles"><h2>Ready the Tiles</h2></a>
+<p>Objects, as with backgrounds, are composed of 8x8 tiles, and if you want
+something bigger than 8x8 you have to use more than one tile put together.
+Object tiles go into the final two charblocks of VRAM (indexes 4 and 5). Because
+there's only two of them, they are sometimes called the lower block
+(<code>0x601_0000</code>) and the higher/upper block (<code>0x601_4000</code>).</p>
+<p>Tile indexes for sprites always offset from the base of the lower block, and
+they always go 32 bytes at a time, regardless of if the object is set for 4bpp
+or 8bpp. From this we can determine that there's 512 tile slots in each of the
+two object charblocks. However, in video modes 3, 4, and 5 the space for the
+background cuts into the lower charblock, so you can only safely use the upper
+charblock.</p>
+<p>With backgrounds you picked every single tile individually with a bunch of
+screen entry values. Objects don't do that at all. Instead you pick a base tile,
+size, and shape, then it figures out the rest from there. However, you may
+recall back with the display control register something about an &quot;object memory
+1d&quot; bit. This is where that comes into play.</p>
+<ul>
+<li>If object memory is set to be 2d (the default) then each charblock is treated
+as 32 tiles by 32 tiles square. Each object has a base tile and dimensions,
+and that just extracts directly from the charblock picture as if you were
+selecting an area. This mode probably makes for the easiest image editing.</li>
+<li>If object memory is set to be 1d then the tiles are loaded sequentially from
+the starting point, enough to fill in the object's dimensions. This most
+probably makes it the easiest to program with about things, since programming
+languages are pretty good at 1d things.</li>
+</ul>
+<p>I'm not sure I explained that well, here's a picture:</p>
+<p><img src="obj_memory_2d1d.jpg" alt="2d1d-diagram" /></p>
+<p>In 2d mode, a new row of tiles starts every 32 tile indexes.</p>
+<p>Of course, the mode that you actually end up using is not particularly
+important, since it should be the job of your image conversion routine to get
+everything all lined up and into place anyway.</p>
+<a class="header" href="#set-the-object-attributes" id="set-the-object-attributes"><h2>Set the Object Attributes</h2></a>
+<p>The final step is to assign the correct attributes to an object. Each object has
+three <code>u16</code> values that make up its overall attributes.</p>
+<p>Before we go into the details, I want to remind you that the hardware will
+attempt to process every single object every single frame, and also that all of
+the GBA's memory is cleared to 0 at startup. Why do these two things matter
+right now? As you'll see in a second an &quot;all zero&quot; set of object attributes
+causes an 8x8 object to appear at 0,0 using object tile index 0. This is usually
+<em>not</em> what you want your unused objects to do. When your game first starts you
+should take a moment to mark any objects you won't be using as objects to not
+render.</p>
+<a class="header" href="#objectattributesattr0" id="objectattributesattr0"><h3>ObjectAttributes.attr0</h3></a>
+<ul>
+<li>8 bits for row coordinate (marks the top of the sprite)</li>
+<li>2 bits for object rendering: 0 = Normal, 1 = Affine, 2 = Disabled, 3 = Affine with double rendering area</li>
+<li>2 bits for object mode: 0 = Normal, 1 = Alpha Blending, 2 = Object Window, 3 = Forbidden</li>
+<li>1 bit for mosaic enabled</li>
+<li>1 bit 8bpp color enabled</li>
+<li>2 bits for shape: 0 = Square, 1 = Horizontal, 2 = Vertical, 3 = Forbidden</li>
+</ul>
+<p>If an object is 128 pixels big at Y &gt; 128 you'll get a strange looking result
+where it acts like Y &gt; -128 and then displays partly off screen to the top.</p>
+<a class="header" href="#objectattributesattr1" id="objectattributesattr1"><h3>ObjectAttributes.attr1</h3></a>
+<ul>
+<li>9 bit for column coordinate (marks the left of the sprite)</li>
+<li>Either:
+<ul>
+<li>3 empty bits, 1 bit for horizontal flip, 1 bit for vertical flip (non-affine)</li>
+<li>5 bits for affine index (affine)</li>
+</ul>
+</li>
+<li>2 bits for size.</li>
+</ul>
+<table><thead><tr><th align="center"> Size </th><th align="center"> Square </th><th align="center"> Horizontal </th><th align="center"> Vertical</th></tr></thead><tbody>
+<tr><td align="center"> 0    </td><td align="center"> 8x8    </td><td align="center"> 16x8       </td><td align="center"> 8x16    </td></tr>
+<tr><td align="center"> 1    </td><td align="center"> 16x16  </td><td align="center"> 32x8       </td><td align="center"> 8x32    </td></tr>
+<tr><td align="center"> 2    </td><td align="center"> 32x32  </td><td align="center"> 32x16      </td><td align="center"> 16x32   </td></tr>
+<tr><td align="center"> 3    </td><td align="center"> 64x64  </td><td align="center"> 64x32      </td><td align="center"> 32x64   </td></tr>
+</tbody></table>
+<a class="header" href="#objectattributesattr2" id="objectattributesattr2"><h3>ObjectAttributes.attr2</h3></a>
+<ul>
+<li>10 bits for the base tile index</li>
+<li>2 bits for priority</li>
+<li>4 bits for the palbank index (4bpp mode only, ignored in 8bpp)</li>
+</ul>
+<a class="header" href="#objectattributes-summary" id="objectattributes-summary"><h3>ObjectAttributes summary</h3></a>
+<p>So I said in the GBA memory mapping section that C people would tell you that
+the object attributes should look like this:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+#[repr(C)]
+pub struct ObjectAttributes {
+  attr0: u16,
+  attr1: u16,
+  attr2: u16,
+  filler: i16,
+}
+#}</code></pre></pre>
+<p>Except that:</p>
+<ol>
+<li>It's wasteful when we store object attributes on their own outside of OAM
+(which we definitely might want to do).</li>
+<li>In Rust we can't access just one field through a volatile pointer (our
+pointers aren't actually volatile to begin with, just the ops we do with them
+are). We have to read or write the whole pointer's value at a time.
+Similarly, we can't do things like <code>|=</code> and <code>&amp;=</code> with volatile in Rust. So in
+rust we can't have a volatile pointer to an ObjectAttributes and then write
+to just the three &quot;real&quot; values and not touch the filler field. Having the
+filler value in there just means we have to dance around it more, not less.</li>
+<li>We want to newtype this whole thing to prevent accidental invalid states from
+being written into memory.</li>
+</ol>
+<p>So we will not be using that representation. At the same time we want to have no
+overhead, so we will stick to three <code>u16</code> values. We could newtype each
+individual field to be its own type (<code>ObjectAttributesAttr0</code> or something silly
+like that), since there aren't actual dependencies between two different fields
+such that a change in one can throw another into a forbidden state. The worst
+that can happen is if we disable or enable affine mode (<code>attr0</code>) it can change
+the meaning of <code>attr1</code>. The changed meaning isn't actually in invalid state
+though, so we <em>could</em> make each field its own type if we wanted.</p>
+<p>However, when you think about it, I can't imagine a common situation where we do
+something like make an <code>attr0</code> value that we then want to save on its own and
+apply to several different <code>ObjectAttributes</code> that we make during a game. That
+just doesn't sound likely to me. So, we'll go the route where <code>ObjectAttributes</code>
+is just a big black box to the outside world and we don't need to think about
+the three fields internally as being separate.</p>
+<p>First we make it so that we can get and set object attributes from memory:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub const OAM: usize = 0x700_0000;
+
+pub fn object_attributes(slot: usize) -&gt; ObjectAttributes {
+  assert!(slot &lt; 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::&lt;u16&gt;() * 4)) as *mut u16);
+  unsafe {
+    ObjectAttributes {
+      attr0: ptr.read(),
+      attr1: ptr.offset(1).read(),
+      attr2: ptr.offset(2).read(),
+    }
+  }
+}
+
+pub fn set_object_attributes(slot: usize, obj: ObjectAttributes) {
+  assert!(slot &lt; 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::&lt;u16&gt;() * 4)) as *mut u16);
+  unsafe {
+    ptr.write(obj.attr0);
+    ptr.offset(1).write(obj.attr1);
+    ptr.offset(2).write(obj.attr2);
+  }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct ObjectAttributes {
+  attr0: u16,
+  attr1: u16,
+  attr2: u16,
+}
+#}</code></pre></pre>
+<p>Then we add a billion methods to the <code>ObjectAttributes</code> type so that we can
+actually set all the different values that we want to set.</p>
+<p>This code block is the last thing on this page so if you don't wanna scroll past
+the whole thing you can just go to the next page.</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectRenderMode {
+  Normal,
+  Affine,
+  Disabled,
+  DoubleAreaAffine,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectMode {
+  Normal,
+  AlphaBlending,
+  ObjectWindow,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectShape {
+  Square,
+  Horizontal,
+  Vertical,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectOrientation {
+  Normal,
+  HFlip,
+  VFlip,
+  BothFlip,
+  Affine(u8),
+}
+
+impl ObjectAttributes {
+  pub fn row(&amp;self) -&gt; u16 {
+    self.attr0 &amp; 0b1111_1111
+  }
+  pub fn column(&amp;self) -&gt; u16 {
+    self.attr1 &amp; 0b1_1111_1111
+  }
+  pub fn rendering(&amp;self) -&gt; ObjectRenderMode {
+    match (self.attr0 &gt;&gt; 8) &amp; 0b11 {
+      0 =&gt; ObjectRenderMode::Normal,
+      1 =&gt; ObjectRenderMode::Affine,
+      2 =&gt; ObjectRenderMode::Disabled,
+      3 =&gt; ObjectRenderMode::DoubleAreaAffine,
+      _ =&gt; unimplemented!(),
+    }
+  }
+  pub fn mode(&amp;self) -&gt; ObjectMode {
+    match (self.attr0 &gt;&gt; 0xA) &amp; 0b11 {
+      0 =&gt; ObjectMode::Normal,
+      1 =&gt; ObjectMode::AlphaBlending,
+      2 =&gt; ObjectMode::ObjectWindow,
+      _ =&gt; unimplemented!(),
+    }
+  }
+  pub fn mosaic(&amp;self) -&gt; bool {
+    ((self.attr0 &lt;&lt; 3) as i16) &lt; 0
+  }
+  pub fn two_fifty_six_colors(&amp;self) -&gt; bool {
+    ((self.attr0 &lt;&lt; 2) as i16) &lt; 0
+  }
+  pub fn shape(&amp;self) -&gt; ObjectShape {
+    match (self.attr0 &gt;&gt; 0xE) &amp; 0b11 {
+      0 =&gt; ObjectShape::Square,
+      1 =&gt; ObjectShape::Horizontal,
+      2 =&gt; ObjectShape::Vertical,
+      _ =&gt; unimplemented!(),
+    }
+  }
+  pub fn orientation(&amp;self) -&gt; ObjectOrientation {
+    if (self.attr0 &gt;&gt; 8) &amp; 1 &gt; 0 {
+      ObjectOrientation::Affine((self.attr1 &gt;&gt; 9) as u8 &amp; 0b1_1111)
+    } else {
+      match (self.attr1 &gt;&gt; 0xC) &amp; 0b11 {
+        0 =&gt; ObjectOrientation::Normal,
+        1 =&gt; ObjectOrientation::HFlip,
+        2 =&gt; ObjectOrientation::VFlip,
+        3 =&gt; ObjectOrientation::BothFlip,
+      }
+    }
+  }
+  pub fn size(&amp;self) -&gt; u16 {
+    self.attr1 &gt;&gt; 0xE
+  }
+  pub fn tile_index(&amp;self) -&gt; u16 {
+    self.attr2 &amp; 0b11_1111_1111
+  }
+  pub fn priority(&amp;self) -&gt; u16 {
+    self.attr2 &gt;&gt; 0xA
+  }
+  pub fn palbank(&amp;self) -&gt; u16 {
+    self.attr2 &gt;&gt; 0xC
+  }
+  //
+  pub fn set_row(&amp;mut self, row: u16) {
+    self.attr0 &amp;= !0b1111_1111;
+    self.attr0 |= row &amp; 0b1111_1111;
+  }
+  pub fn set_column(&amp;mut self, col: u16) {
+    self.attr1 &amp;= !0b1_1111_1111;
+    self.attr2 |= col &amp; 0b1_1111_1111;
+  }
+  pub fn set_rendering(&amp;mut self, rendering: ObjectRenderMode) {
+    const RENDERING_MASK: u16 = 0b11 &lt;&lt; 8;
+    self.attr0 &amp;= !RENDERING_MASK;
+    self.attr0 |= (rendering as u16) &lt;&lt; 8;
+  }
+  pub fn set_mode(&amp;mut self, mode: ObjectMode) {
+    const MODE_MASK: u16 = 0b11 &lt;&lt; 0xA;
+    self.attr0 &amp;= MODE_MASK;
+    self.attr0 |= (mode as u16) &lt;&lt; 0xA;
+  }
+  pub fn set_mosaic(&amp;mut self, bit: bool) {
+    const MOSAIC_BIT: u16 = 1 &lt;&lt; 0xC;
+    if bit {
+      self.attr0 |= MOSAIC_BIT
+    } else {
+      self.attr0 &amp;= !MOSAIC_BIT
+    }
+  }
+  pub fn set_two_fifty_six_colors(&amp;mut self, bit: bool) {
+    const COLOR_MODE_BIT: u16 = 1 &lt;&lt; 0xD;
+    if bit {
+      self.attr0 |= COLOR_MODE_BIT
+    } else {
+      self.attr0 &amp;= !COLOR_MODE_BIT
+    }
+  }
+  pub fn set_shape(&amp;mut self, shape: ObjectShape) {
+    self.attr0 &amp;= 0b0011_1111_1111_1111;
+    self.attr0 |= (shape as u16) &lt;&lt; 0xE;
+  }
+  pub fn set_orientation(&amp;mut self, orientation: ObjectOrientation) {
+    const AFFINE_INDEX_MASK: u16 = 0b1_1111 &lt;&lt; 9;
+    self.attr1 &amp;= !AFFINE_INDEX_MASK;
+    let bits = match orientation {
+      ObjectOrientation::Affine(index) =&gt; (index as u16) &lt;&lt; 9,
+      ObjectOrientation::Normal =&gt; 0,
+      ObjectOrientation::HFlip =&gt; 1 &lt;&lt; 0xC,
+      ObjectOrientation::VFlip =&gt; 1 &lt;&lt; 0xD,
+      ObjectOrientation::BothFlip =&gt; 0b11 &lt;&lt; 0xC,
+    };
+    self.attr1 |= bits;
+  }
+  pub fn set_size(&amp;mut self, size: u16) {
+    self.attr1 &amp;= 0b0011_1111_1111_1111;
+    self.attr1 |= size &lt;&lt; 14;
+  }
+  pub fn set_tile_index(&amp;mut self, index: u16) {
+    self.attr2 &amp;= !0b11_1111_1111;
+    self.attr2 |= 0b11_1111_1111 &amp; index;
+  }
+  pub fn set_priority(&amp;mut self, priority: u16) {
+    self.attr2 &amp;= !0b0000_1100_0000_0000;
+    self.attr2 |= (priority &amp; 0b11) &lt;&lt; 0xA;
+  }
+  pub fn set_palbank(&amp;mut self, palbank: u16) {
+    self.attr2 &amp;= !0b1111_0000_0000_0000;
+    self.attr2 |= (palbank &amp; 0b1111) &lt;&lt; 0xC;
+  }
+}
+#}</code></pre></pre>
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docs/ch03/tile_data.html

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-            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html" class="active"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="../ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="../ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="../ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="../ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="../ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="../ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="../ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="../ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="../ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="../ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="../ch03/tile_data.html" class="active"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="../ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="../ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="../ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="../ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
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-            <ol class="chapter"><li><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
         </nav>
 
         <div id="page-wrapper" class="page-wrapper">
@@ -157,7 +157,9 @@ directory</a> of the repo
 if you want to get them that way.</p>
 <a class="header" href="#expected-knowledge" id="expected-knowledge"><h2>Expected Knowledge</h2></a>
 <p>I will try not to ask too much of the reader ahead of time, but you are expected
-to have already read <a href="https://doc.rust-lang.org/book/">The Rust Book</a>.</p>
+to have already read <a href="https://doc.rust-lang.org/book/">The Rust Book</a>. Having
+also read through the <a href="https://doc.rust-lang.org/nomicon/">Rustonomicon</a> is
+appreciated but not required.</p>
 <p>It's very difficult to know when you've said something that someone else won't
 already know about, or if you're presenting ideas out of order. If things aren't
 clear please <a href="https://github.com/rust-console/gba/issues">file an issue</a> and
@@ -176,14 +178,11 @@ folks in the server as well (there's a few hundred folks).</p>
 <p>If you want to read more about developing on the GBA there are some other good
 resources as well:</p>
 <ul>
-<li><a href="https://www.coranac.com/tonc/text/toc.htm">Tonc</a>, a tutorial series written
+<li><a href="https://www.coranac.com/tonc/text/toc.htm">TONC</a>, a tutorial series written
 for C, but it's what I based the ordering of this book's sections on.</li>
 <li><a href="http://problemkaputt.de/gbatek.htm">GBATEK</a>, a homebrew tech manual for
 GBA/NDS/DSi. We will regularly link to parts of it when talking about various
 bits of the GBA.</li>
-<li><a href="https://www.cs.rit.edu/%7Etjh8300/CowBite/CowBiteSpec.htm">CowBite</a> is another
-tech specification that's more GBA specific. It's sometimes got more ASCII
-art diagrams and example C struct layouts than GBATEK does.</li>
 </ul>
 
                     </main>

docs/introduction.html

@@ -72,7 +72,7 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <ol class="chapter"><li><a href="introduction.html" class="active"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="introduction.html" class="active"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
         </nav>
 
         <div id="page-wrapper" class="page-wrapper">
@@ -157,7 +157,9 @@ directory</a> of the repo
 if you want to get them that way.</p>
 <a class="header" href="#expected-knowledge" id="expected-knowledge"><h2>Expected Knowledge</h2></a>
 <p>I will try not to ask too much of the reader ahead of time, but you are expected
-to have already read <a href="https://doc.rust-lang.org/book/">The Rust Book</a>.</p>
+to have already read <a href="https://doc.rust-lang.org/book/">The Rust Book</a>. Having
+also read through the <a href="https://doc.rust-lang.org/nomicon/">Rustonomicon</a> is
+appreciated but not required.</p>
 <p>It's very difficult to know when you've said something that someone else won't
 already know about, or if you're presenting ideas out of order. If things aren't
 clear please <a href="https://github.com/rust-console/gba/issues">file an issue</a> and
@@ -176,14 +178,11 @@ folks in the server as well (there's a few hundred folks).</p>
 <p>If you want to read more about developing on the GBA there are some other good
 resources as well:</p>
 <ul>
-<li><a href="https://www.coranac.com/tonc/text/toc.htm">Tonc</a>, a tutorial series written
+<li><a href="https://www.coranac.com/tonc/text/toc.htm">TONC</a>, a tutorial series written
 for C, but it's what I based the ordering of this book's sections on.</li>
 <li><a href="http://problemkaputt.de/gbatek.htm">GBATEK</a>, a homebrew tech manual for
 GBA/NDS/DSi. We will regularly link to parts of it when talking about various
 bits of the GBA.</li>
-<li><a href="https://www.cs.rit.edu/%7Etjh8300/CowBite/CowBiteSpec.htm">CowBite</a> is another
-tech specification that's more GBA specific. It's sometimes got more ASCII
-art diagrams and example C struct layouts than GBATEK does.</li>
 </ul>
 
                     </main>

docs/print.html

@@ -72,7 +72,7 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <ol class="chapter"><li><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="ch03/object_basics.html"><strong aria-hidden="true">5.4.</strong> Object Basics</a></li><li><a href="ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
+            <ol class="chapter"><li><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch00/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch01/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch01/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch01/volatile.html"><strong aria-hidden="true">3.2.</strong> Volatile</a></li><li><a href="ch01/io_registers.html"><strong aria-hidden="true">3.3.</strong> IO Registers</a></li><li><a href="ch01/the_display_control_register.html"><strong aria-hidden="true">3.4.</strong> The Display Control Register</a></li><li><a href="ch01/video_memory_intro.html"><strong aria-hidden="true">3.5.</strong> Video Memory Intro</a></li><li><a href="ch01/hello2.html"><strong aria-hidden="true">3.6.</strong> hello2</a></li></ol></li><li><a href="ch02/index.html"><strong aria-hidden="true">4.</strong> Ch 2: User Input</a></li><li><ol class="section"><li><a href="ch02/the_key_input_register.html"><strong aria-hidden="true">4.1.</strong> The Key Input Register</a></li><li><a href="ch02/the_vcount_register.html"><strong aria-hidden="true">4.2.</strong> The VCount Register</a></li><li><a href="ch02/light_cycle.html"><strong aria-hidden="true">4.3.</strong> light_cycle</a></li></ol></li><li><a href="ch03/index.html"><strong aria-hidden="true">5.</strong> Ch 3: Memory and Objects</a></li><li><ol class="section"><li><a href="ch03/gba_memory_mapping.html"><strong aria-hidden="true">5.1.</strong> GBA Memory Mapping</a></li><li><a href="ch03/tile_data.html"><strong aria-hidden="true">5.2.</strong> Tile Data</a></li><li><a href="ch03/regular_backgrounds.html"><strong aria-hidden="true">5.3.</strong> Regular Backgrounds</a></li><li><a href="ch03/regular_objects.html"><strong aria-hidden="true">5.4.</strong> Regular Objects</a></li><li><a href="ch03/gba_rng.html"><strong aria-hidden="true">5.5.</strong> GBA RNG</a></li><li><a href="ch03/memory_game.html"><strong aria-hidden="true">5.6.</strong> memory_game</a></li></ol></li></ol>
         </nav>
 
         <div id="page-wrapper" class="page-wrapper">
@@ -157,7 +157,9 @@ directory</a> of the repo
 if you want to get them that way.</p>
 <a class="header" href="#expected-knowledge" id="expected-knowledge"><h2>Expected Knowledge</h2></a>
 <p>I will try not to ask too much of the reader ahead of time, but you are expected
-to have already read <a href="https://doc.rust-lang.org/book/">The Rust Book</a>.</p>
+to have already read <a href="https://doc.rust-lang.org/book/">The Rust Book</a>. Having
+also read through the <a href="https://doc.rust-lang.org/nomicon/">Rustonomicon</a> is
+appreciated but not required.</p>
 <p>It's very difficult to know when you've said something that someone else won't
 already know about, or if you're presenting ideas out of order. If things aren't
 clear please <a href="https://github.com/rust-console/gba/issues">file an issue</a> and
@@ -176,14 +178,11 @@ folks in the server as well (there's a few hundred folks).</p>
 <p>If you want to read more about developing on the GBA there are some other good
 resources as well:</p>
 <ul>
-<li><a href="https://www.coranac.com/tonc/text/toc.htm">Tonc</a>, a tutorial series written
+<li><a href="https://www.coranac.com/tonc/text/toc.htm">TONC</a>, a tutorial series written
 for C, but it's what I based the ordering of this book's sections on.</li>
 <li><a href="http://problemkaputt.de/gbatek.htm">GBATEK</a>, a homebrew tech manual for
 GBA/NDS/DSi. We will regularly link to parts of it when talking about various
 bits of the GBA.</li>
-<li><a href="https://www.cs.rit.edu/%7Etjh8300/CowBite/CowBiteSpec.htm">CowBite</a> is another
-tech specification that's more GBA specific. It's sometimes got more ASCII
-art diagrams and example C struct layouts than GBATEK does.</li>
 </ul>
 <a class="header" href="#chapter-0-development-setup" id="chapter-0-development-setup"><h1>Chapter 0: Development Setup</h1></a>
 <p>Before you can build a GBA game you'll have to follow some special steps to
@@ -1302,6 +1301,23 @@ without trading away too much in terms of quality.</p>
 <p>To top it all off, we'll make a simple &quot;memory game&quot; sort of thing. There's some
 face down cards in a grid, you pick one to check, then you pick the other to
 check, and then if they match the pair disappears.</p>
+<a class="header" href="#drawing-priority" id="drawing-priority"><h2>Drawing Priority</h2></a>
+<p>Both backgrounds and objects can have &quot;priority&quot; values associated with them.
+TONC and GBATEK have <em>opposite</em> ideas of what it means to have the &quot;highest&quot;
+priority. TONC goes by highest numerical value, and GBATEK goes by what's on the
+z-layer closest to the user. Let's list out the rules as clearly as we can:</p>
+<ul>
+<li>Priority is always two bits, so 0 through 3.</li>
+<li>Priority conceptually proceeds in drawing passes that count <em>down</em>, so any
+priority 3 things can get covered up by priority 2 things. In truth there's
+probably depth testing and buffering stuff going on so it's all one single
+pass, but conceptually we will imagine it happening as all of the 3 elements,
+then all of 2, and so on.</li>
+<li>Objects always draw over top of backgrounds of equal priority.</li>
+<li>Within things of the same type and priority, the lower numbered element &quot;wins&quot;
+and gets its pixel drawn (bg0 is favored over bg1, obj0 is favored over obj1,
+etc).</li>
+</ul>
 <a class="header" href="#gba-memory-mapping" id="gba-memory-mapping"><h1>GBA Memory Mapping</h1></a>
 <p>The <a href="http://problemkaputt.de/gbatek.htm#gbamemorymap">GBA Memory Map</a> has
 several memory portions to it, each with their own little differences. Most of
@@ -1391,6 +1407,20 @@ and then a <em>separate</em> setting outside of the graphical data determines wh
 palbank is to be used for that background or object (the screen entry data for
 backgrounds, and the object attributes for objects).</li>
 </ul>
+<a class="header" href="#transparency" id="transparency"><h3>Transparency</h3></a>
+<p>When a pixel within a background or object specifies index 0 as its palette
+entry it is treated as a transparent pixel. This means that in 8bpp mode there's
+only 255 actual color options (0 being transparent), and in 4bpp mode there's
+only 15 actual color options available within each palbank (the 0th entry of
+<em>each</em> palbank is transparent).</p>
+<p>Individual backgrounds, and individual objects, each determine if they're 4bpp
+or 8bpp separately, so a given overall palette slot might map to a used color in
+8bpp and an unused/transparent color in 4bpp. If you're a palette wizard.</p>
+<p>Palette slot 0 of the overall background palette is used to determine the
+&quot;backdrop&quot; color. That's the color you see if no background or object ends up
+being rendered within a given pixel.</p>
+<p>Since display mode 3 and display mode 5 don't use the palette, they cannot
+benefit from transparency.</p>
 <a class="header" href="#video-ram--vram" id="video-ram--vram"><h2>Video RAM / VRAM</h2></a>
 <ul>
 <li><code>0x6000000</code> to <code>0x6017FFF</code> (96k)</li>
@@ -1630,10 +1660,660 @@ example</a></li>
 macro to have the formatted resource be available as a const value you can
 load at runtime.</li>
 </ol>
-<a class="header" href="#tiled-backgrounds" id="tiled-backgrounds"><h1>Tiled Backgrounds</h1></a>
+<a class="header" href="#regular-backgrounds" id="regular-backgrounds"><h1>Regular Backgrounds</h1></a>
-<p>TODO</p>
+<p>So, backgrounds, they're cool. Why do we call the ones here &quot;regular&quot;
-<a class="header" href="#object-basics" id="object-basics"><h1>Object Basics</h1></a>
+backgrounds? Because there's also &quot;affine&quot; backgrounds. However, affine math
-<p>TODO</p>
+stuff adds a complication, so for now we'll just work with regular backgrounds.
+The non-affine backgrounds are sometimes called &quot;text mode&quot; backgrounds by other
+guides.</p>
+<p>To get your background image working you generally need to perform all of the
+following steps, though I suppose the exact ordering is up to you.</p>
+<a class="header" href="#tiled-video-modes" id="tiled-video-modes"><h2>Tiled Video Modes</h2></a>
+<p>When you want regular tiled display, you must use video mode 0 or 1.</p>
+<ul>
+<li>Mode 0 allows for using all four BG layers (0 through 3) as regular
+backgrounds.</li>
+<li>Mode 1 allows for using BG0 and BG1 as regular backgrounds, BG2 as an affine
+background, and BG3 not at all.</li>
+<li>Mode 2 allows for BG2 and BG3 to be used as affine backgrounds, while BG0 and
+BG1 cannot be used at all.</li>
+</ul>
+<p>We will not cover affine backgrounds in this chapter, so we will naturally be
+using video mode 0.</p>
+<p>Also, note that you have to enable each background layer that you want to use
+within the display control register.</p>
+<a class="header" href="#get-your-palette-ready" id="get-your-palette-ready"><h2>Get Your Palette Ready</h2></a>
+<p>Background palette starts at <code>0x5000000</code> and is 256 <code>u16</code> values long. It'd
+potentially be possible declare a static array starting at a fixed address and
+use a linker script to make sure that it ends up at the right spot in the final
+program, but since we have to use volatile reads and writes with PALRAM anyway,
+we'll just reuse our <code>VolatilePtr</code> type. Something like this:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub const PALRAM_BG_BASE: VolatilePtr&lt;u16&gt; = VolatilePtr(0x500_0000 as *mut u16);
+
+pub fn bg_palette(slot: usize) -&gt; u16 {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_BG_BASE.offset(slot as isize).read() }
+}
+
+pub fn set_bg_palette(slot: usize, color: u16) {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_BG_BASE.offset(slot as isize).write(color) }
+}
+#}</code></pre></pre>
+<p>As we discussed with the tile color depths, the palette can be utilized as a
+single block of palette values (<code>[u16; 256]</code>) or as 16 palbanks of 16 palette
+values each (<code>[[u16;16]; 16]</code>). This setting is assigned per background layer
+via IO register.</p>
+<a class="header" href="#get-your-tiles-ready" id="get-your-tiles-ready"><h2>Get Your Tiles Ready</h2></a>
+<p>Tile data is placed into charblocks. A charblock is always 16kb, so depending on
+color depth it will have either 256 or 512 tiles within that charblock.
+Charblocks 0, 1, 2, and 3 are all for background tiles. That's a maximum of 2048
+tiles for backgrounds, but as you'll see in a moment a particular tilemap entry
+can't even index that high. Instead, each background layer is assigned a
+&quot;character base block&quot;, and then tilemap entries index relative to the character
+base block of that background layer.</p>
+<p>Now, if you want to move in a lot of tile data you'll probably want to use a DMA
+routine, or at least write a function like memcopy32 for fast <code>u32</code> copying from
+ROM into VRAM. However, for now, and because we're being very explicit since
+this is our first time doing it, we'll write it as functions for individual tile
+reads and writes.</p>
+<p>The math works like indexing a pointer, except that we have two sizes we need to
+go by. First you take the base address for VRAM (<code>0x600_0000</code>), then add the
+size of a charblock (16kb) times the charblock you want to place the tile
+within, and then you add the index of the tile slot you're placing it into times
+the size of that type of tile. Like this:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub fn bg_tile_4pp(base_block: usize, tile_index: usize) -&gt; Tile4bpp {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 512);
+  let address = VRAM + size_of::&lt;Charblock4bpp&gt;() * base_block + size_of::&lt;Tile4bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile4bpp).read() }
+}
+
+pub fn set_bg_tile_4pp(base_block: usize, tile_index: usize, tile: Tile4bpp) {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 512);
+  let address = VRAM + size_of::&lt;Charblock4bpp&gt;() * base_block + size_of::&lt;Tile4bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile4bpp).write(tile) }
+}
+
+pub fn bg_tile_8pp(base_block: usize, tile_index: usize) -&gt; Tile8bpp {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 256);
+  let address = VRAM + size_of::&lt;Charblock8bpp&gt;() * base_block + size_of::&lt;Tile8bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile8bpp).read() }
+}
+
+pub fn set_bg_tile_8pp(base_block: usize, tile_index: usize, tile: Tile8bpp) {
+  assert!(base_block &lt; 4);
+  assert!(tile_index &lt; 256);
+  let address = VRAM + size_of::&lt;Charblock8bpp&gt;() * base_block + size_of::&lt;Tile8bpp&gt;() * tile_index;
+  unsafe { VolatilePtr(address as *mut Tile8bpp).write(tile) }
+}
+#}</code></pre></pre>
+<p>For bulk operations, you'd do the exact same math to get your base destination
+pointer, and then you'd get the base source pointer for the tile you're copying
+out of ROM, and then you'd do the bulk copy for the correct number of <code>u32</code>
+values that you're trying to move (8 per tile moved for 4bpp, or 16 per tile
+moved for 8bpp).</p>
+<p><strong>GBA Limitation Note:</strong> on a modern PC (eg: <code>x86</code> or <code>x86_64</code>) you're probably
+used to index based loops and iterator based loops being the same speed. The CPU
+has the ability to do a &quot;fused multiply add&quot;, so the base address of the array
+plus desired index * size per element is a single CPU operation to compute. It's
+slightly more complicated if there's arrays within arrays like there are here,
+but with normal arrays it's basically the same speed to index per loop cycle as
+it is to take a base address and then add +1 offset per loop cycle. However, the
+GBA's CPU <em>can't do any of that</em>. On the GBA, there's a genuine speed difference
+between looping over indexes and then indexing each loop (slow) compared to
+using an iterator that just stores an internal pointer and does +1 offset per
+loop until it reaches the end (fast). The repeated indexing itself can by itself
+be an expensive step. If it's like a 3 element array it's no big deal, but if
+you've got a big slice of data to process, be sure to go over it with <code>.iter()</code>
+and <code>.iter_mut()</code> if you can, instead of looping by index. This is Rust and all,
+so probably you were gonna do that anyway, but just a heads up.</p>
+<a class="header" href="#get-your-tilemap-ready" id="get-your-tilemap-ready"><h2>Get your Tilemap ready</h2></a>
+<p>I believe that at one point I alluded to a tilemap existing. Well, just as the
+tiles are arranged into charblocks, the data describing what tile to show in
+what location is arranged into a thing called a <strong>screenblock</strong>.</p>
+<p>A screenblock is placed into VRAM the same as the tile data charblocks. Starting
+at the base of VRAM (<code>0x600_0000</code>) there are 32 slots for the screenblock array.
+Each screenblock is 2048 bytes (<code>0x800</code>). Naturally, if our tiles are using up
+charblock space within VRAM and our tilemaps are using up screenblock space
+within the same VRAM... well it would just be a <em>disaster</em> if they ran in to
+each other. Once again, it's up to you as the programmer to determine how much
+space you want to devote to each thing. Each complete charblock uses up 8
+screenblocks worth of space, but you don't have to fill a complete charblock
+with tiles, so you can be very fiddly with how you split the memory.</p>
+<p>Each screenblock is composed of a series of <em>screenblock entry</em> values, which
+describe what tile index to use and if the tile should be flipped and what
+palbank it should use (if any). Because both regular backgrounds and affine
+backgrounds are composed of screenblocks with entries, and because the affine
+background has a smaller format for screenblock entries, we'll name
+appropriately.</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+#[derive(Clone, Copy)]
+#[repr(transparent)]
+pub struct RegularScreenblock {
+  data: [RegularScreenblockEntry; 32 * 32],
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+#[repr(transparent)]
+pub struct RegularScreenblockEntry(u16);
+#}</code></pre></pre>
+<p>So, with one entry per tile, a single screenblock allows for 32x32 tiles worth of
+background.</p>
+<p>The format of a regular screenblock entry is quite simple compared to some of
+the IO register stuff:</p>
+<ul>
+<li>10 bits for tile index (base off of the character base block of the background)</li>
+<li>1 bit for horizontal flip</li>
+<li>1 bit for vertical flip</li>
+<li>4 bits for picking which palbank to use (if 4bpp, otherwise it's ignored)</li>
+</ul>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+impl RegularScreenblockEntry {
+  pub fn tile_id(self) -&gt; u16 {
+    self.0 &amp; 0b11_1111_1111
+  }
+  pub fn set_tile_id(&amp;mut self, id: u16) {
+    self.0 &amp;= !0b11_1111_1111;
+    self.0 |= id;
+  }
+  pub fn horizontal_flip(self) -&gt; bool {
+    (self.0 &amp; (1 &lt;&lt; 0xA)) &gt; 0
+  }
+  pub fn set_horizontal_flip(&amp;mut self, bit: bool) {
+    if bit {
+      self.0 |= 1 &lt;&lt; 0xA;
+    } else {
+      self.0 &amp;= !(1 &lt;&lt; 0xA);
+    }
+  }
+  pub fn vertical_flip(self) -&gt; bool {
+    (self.0 &amp; (1 &lt;&lt; 0xB)) &gt; 0
+  }
+  pub fn set_vertical_flip(&amp;mut self, bit: bool) {
+    if bit {
+      self.0 |= 1 &lt;&lt; 0xB;
+    } else {
+      self.0 &amp;= !(1 &lt;&lt; 0xB);
+    }
+  }
+  pub fn palbank_index(self) -&gt; u16 {
+    self.0 &gt;&gt; 12
+  }
+  pub fn set_palbank_index(&amp;mut self, palbank_index: u16) {
+    self.0 &amp;= 0b1111_1111_1111;
+    self.0 |= palbank_index;
+  }
+}
+#}</code></pre></pre>
+<p>Now, at either 256 or 512 tiles per charblock, you might be thinking that with a
+10 bit index you can index past the end of one charblock and into the next.
+You'd be right, mostly.</p>
+<p>As long as you stay within the background memory region for charblocks (that is,
+0 through 3), then it all works out. However, if you try to get the background
+rendering to reach outside of the background charblocks you'll get an
+implementation defined result. It's not the dreaded &quot;undefined behavior&quot; we're
+often worried about in programming, but the results <em>are</em> determined by what
+you're running the game on. With GBA hardware you get a bizarre result
+(basically another way to put garbage on the screen). With a DS it acts as if
+the tiles were all 0s. If you use an emulator it might or might not allow for
+you to do this, it's up to the emulator writers.</p>
+<a class="header" href="#set-your-io-registers" id="set-your-io-registers"><h2>Set Your IO Registers</h2></a>
+<p>Instead of being just a single IO register to learn about this time, there's two
+separate groups of related registers.</p>
+<a class="header" href="#background-control" id="background-control"><h3>Background Control</h3></a>
+<ul>
+<li>BG0CNT (<code>0x400_0008</code>): BG0 Control</li>
+<li>BG1CNT (<code>0x400_000A</code>): BG1 Control</li>
+<li>BG2CNT (<code>0x400_000C</code>): BG2 Control</li>
+<li>BG3CNT (<code>0x400_000E</code>): BG3 Control</li>
+</ul>
+<p>Each of these are a read/write <code>u16</code> location. This is where we get to all of
+the important details that we've been putting off.</p>
+<ul>
+<li>2 bits for the priority.</li>
+<li>2 bits for &quot;character base block&quot;, the charblock that all of the tile indexes
+for this background are offset from.</li>
+<li>1 bit for mosaic effect being enabled (we'll get to that below).</li>
+<li>1 bit to enable 8bpp, otherwise 4bpp is used.</li>
+<li>5 bits to pick the &quot;screen base block&quot;, the screen block that serves as the
+<em>base</em> value for this background.</li>
+<li>1 bit that is <em>not</em> used in regular mode, but in affine mode it can be enabled
+to cause the affine background to wrap around at the edges.</li>
+<li>2 bits for the background size.</li>
+</ul>
+<p>The size works a little funny. When size is 0 only the base screen block is
+used. If size is 1 or 2 then the base screenblock and the following screenblock
+are placed next to each other (horizontally for 1, vertically for 2). If the
+size is 3 then the base screenblock and the following three screenblocks are
+arranged into a 2x2 grid of screenblocks.</p>
+<a class="header" href="#background-offset" id="background-offset"><h3>Background Offset</h3></a>
+<ul>
+<li>BG0HOFS (<code>0x400_0010</code>): BG0 X-Offset</li>
+<li>BG0VOFS (<code>0x400_0012</code>): BG0 Y-Offset</li>
+<li>BG1HOFS (<code>0x400_0014</code>): BG1 X-Offset</li>
+<li>BG1VOFS (<code>0x400_0016</code>): BG1 Y-Offset</li>
+<li>BG2HOFS (<code>0x400_0018</code>): BG2 X-Offset</li>
+<li>BG2VOFS (<code>0x400_001A</code>): BG2 Y-Offset</li>
+<li>BG3HOFS (<code>0x400_001C</code>): BG3 X-Offset</li>
+<li>BG3VOFS (<code>0x400_001E</code>): BG3 Y-Offset</li>
+</ul>
+<p>Each of these are a <em>write only</em> <code>u16</code> location. Bits 0 through 8 are used, so
+the offsets can be 0 through 511. They also only apply in regular backgrounds.
+If a background is in an affine state then you'll use different IO registers to
+control it (discussed in a later chapter).</p>
+<p>The offset that you assign determines the pixel offset of the display area
+relative to the start of the background scene, as if the screen was a camera
+looking at the scene. In other words, as a BG X offset value increases, you can
+think of it as the camera moving to the right, or as that background moving to
+the left. Like when mario walks toward the goal. Similarly, when a BG Y offset
+increases the camera is moving down, or the background is moving up, like when
+mario falls down from a high platform.</p>
+<p>Depending on how much the background is scrolled and the size of the background,
+it will loop.</p>
+<a class="header" href="#mosaic" id="mosaic"><h2>Mosaic</h2></a>
+<p>As a special effect, you can apply mosaic to backgrounds and objects. It's just
+a single flag for each background, so all backgrounds will use the same mosaic
+settings when they have it enabled. What it actually does is split the normal
+image into &quot;blocks&quot; and then each block gets the color of the top left pixel of
+that block. This is the effect you see when link hits an electric foe with his
+sword and the whole screen &quot;buzzes&quot; at you.</p>
+<p>The mosaic control is a <em>write only</em> <code>u16</code> IO register at <code>0x400_004C</code>.</p>
+<p>There's 4 bits each for:</p>
+<ul>
+<li>Horizontal BG stretch</li>
+<li>Vertical BG stretch</li>
+<li>Horizontal object stretch</li>
+<li>Vertical object stretch</li>
+</ul>
+<p>The inputs should be 1 <em>less</em> than the desired block size. So if you set a
+stretch value of 5 then pixels 0-5 would be part of the first block (6 pixels),
+then 6-11 is the next block (another 6 pixels) and so on.</p>
+<p>If you need to make a pixel other than the top left part of each block the one
+that determines the mosaic color you can carefully offset the background or
+image by a tiny bit, but of course that makes every mosaic block change its
+target pixel. You can't change the target pixel on a block by block basis.</p>
+<a class="header" href="#regular-objects" id="regular-objects"><h1>Regular Objects</h1></a>
+<p>As with backgrounds, objects can be used in both an affine and non-affine way.
+For this section we'll focus on the non-affine elements, and then we'll do all
+the affine stuff in a later chapter.</p>
+<a class="header" href="#objects-vs-sprites" id="objects-vs-sprites"><h2>Objects vs Sprites</h2></a>
+<p>As <a href="https://www.coranac.com/tonc/text/regobj.htm">TONC</a> helpfully reminds us
+(and then proceeds to not follow its own advice), we should always try to think
+in terms of <em>objects</em>, not <em>sprites</em>. A sprite is a logical / software concern,
+perhaps a player concern, whereas an object is a hardware concern.</p>
+<p>What's more, a given sprite that the player sees might need more than one object
+to display. Objects must be either square or rectangular (so sprite bits that
+stick out probably call for a second object), and can only be from 8x8 to 64x64
+(so anything bigger has to be two objects lined up to appear as one).</p>
+<a class="header" href="#general-object-info" id="general-object-info"><h2>General Object Info</h2></a>
+<p>Unlike with backgrounds, you can enable the object layer in any video mode.
+There's space for 128 object definitions in OAM.</p>
+<p>The display gets a number of cycles per scanline to process objects: 1210 by
+default, but only 954 if you enable the &quot;HBlank interval free&quot; setting in the
+display control register. The <a href="http://problemkaputt.de/gbatek.htm#lcdobjoverview">cycle cost per
+object</a> depends on the
+object's size and if it's using affine or regular mode, so enabling the HBlank
+interval free setting doesn't cut the number of objects displayable by an exact
+number of objects. The objects are processed in order of their definitions and
+if you run out of cycles then the rest just don't get shown. If there's a
+concern that you might run out of cycles you can place important objects (such
+as the player) at the start of the list and then less important animation
+objects later on.</p>
+<a class="header" href="#ready-the-palette" id="ready-the-palette"><h2>Ready the Palette</h2></a>
+<p>Objects use the palette the same as the background does. The only difference is
+that the palette data for objects starts at <code>0x500_0200</code>.</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub const PALRAM_OBJECT_BASE: VolatilePtr&lt;u16&gt; = VolatilePtr(0x500_0200 as *mut u16);
+
+pub fn object_palette(slot: usize) -&gt; u16 {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).read() }
+}
+
+pub fn set_object_palette(slot: usize, color: u16) {
+  assert!(slot &lt; 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).write(color) }
+}
+#}</code></pre></pre>
+<a class="header" href="#ready-the-tiles" id="ready-the-tiles"><h2>Ready the Tiles</h2></a>
+<p>Objects, as with backgrounds, are composed of 8x8 tiles, and if you want
+something bigger than 8x8 you have to use more than one tile put together.
+Object tiles go into the final two charblocks of VRAM (indexes 4 and 5). Because
+there's only two of them, they are sometimes called the lower block
+(<code>0x601_0000</code>) and the higher/upper block (<code>0x601_4000</code>).</p>
+<p>Tile indexes for sprites always offset from the base of the lower block, and
+they always go 32 bytes at a time, regardless of if the object is set for 4bpp
+or 8bpp. From this we can determine that there's 512 tile slots in each of the
+two object charblocks. However, in video modes 3, 4, and 5 the space for the
+background cuts into the lower charblock, so you can only safely use the upper
+charblock.</p>
+<p>With backgrounds you picked every single tile individually with a bunch of
+screen entry values. Objects don't do that at all. Instead you pick a base tile,
+size, and shape, then it figures out the rest from there. However, you may
+recall back with the display control register something about an &quot;object memory
+1d&quot; bit. This is where that comes into play.</p>
+<ul>
+<li>If object memory is set to be 2d (the default) then each charblock is treated
+as 32 tiles by 32 tiles square. Each object has a base tile and dimensions,
+and that just extracts directly from the charblock picture as if you were
+selecting an area. This mode probably makes for the easiest image editing.</li>
+<li>If object memory is set to be 1d then the tiles are loaded sequentially from
+the starting point, enough to fill in the object's dimensions. This most
+probably makes it the easiest to program with about things, since programming
+languages are pretty good at 1d things.</li>
+</ul>
+<p>I'm not sure I explained that well, here's a picture:</p>
+<p><img src="obj_memory_2d1d.jpg" alt="2d1d-diagram" /></p>
+<p>In 2d mode, a new row of tiles starts every 32 tile indexes.</p>
+<p>Of course, the mode that you actually end up using is not particularly
+important, since it should be the job of your image conversion routine to get
+everything all lined up and into place anyway.</p>
+<a class="header" href="#set-the-object-attributes" id="set-the-object-attributes"><h2>Set the Object Attributes</h2></a>
+<p>The final step is to assign the correct attributes to an object. Each object has
+three <code>u16</code> values that make up its overall attributes.</p>
+<p>Before we go into the details, I want to remind you that the hardware will
+attempt to process every single object every single frame, and also that all of
+the GBA's memory is cleared to 0 at startup. Why do these two things matter
+right now? As you'll see in a second an &quot;all zero&quot; set of object attributes
+causes an 8x8 object to appear at 0,0 using object tile index 0. This is usually
+<em>not</em> what you want your unused objects to do. When your game first starts you
+should take a moment to mark any objects you won't be using as objects to not
+render.</p>
+<a class="header" href="#objectattributesattr0" id="objectattributesattr0"><h3>ObjectAttributes.attr0</h3></a>
+<ul>
+<li>8 bits for row coordinate (marks the top of the sprite)</li>
+<li>2 bits for object rendering: 0 = Normal, 1 = Affine, 2 = Disabled, 3 = Affine with double rendering area</li>
+<li>2 bits for object mode: 0 = Normal, 1 = Alpha Blending, 2 = Object Window, 3 = Forbidden</li>
+<li>1 bit for mosaic enabled</li>
+<li>1 bit 8bpp color enabled</li>
+<li>2 bits for shape: 0 = Square, 1 = Horizontal, 2 = Vertical, 3 = Forbidden</li>
+</ul>
+<p>If an object is 128 pixels big at Y &gt; 128 you'll get a strange looking result
+where it acts like Y &gt; -128 and then displays partly off screen to the top.</p>
+<a class="header" href="#objectattributesattr1" id="objectattributesattr1"><h3>ObjectAttributes.attr1</h3></a>
+<ul>
+<li>9 bit for column coordinate (marks the left of the sprite)</li>
+<li>Either:
+<ul>
+<li>3 empty bits, 1 bit for horizontal flip, 1 bit for vertical flip (non-affine)</li>
+<li>5 bits for affine index (affine)</li>
+</ul>
+</li>
+<li>2 bits for size.</li>
+</ul>
+<table><thead><tr><th align="center"> Size </th><th align="center"> Square </th><th align="center"> Horizontal </th><th align="center"> Vertical</th></tr></thead><tbody>
+<tr><td align="center"> 0    </td><td align="center"> 8x8    </td><td align="center"> 16x8       </td><td align="center"> 8x16    </td></tr>
+<tr><td align="center"> 1    </td><td align="center"> 16x16  </td><td align="center"> 32x8       </td><td align="center"> 8x32    </td></tr>
+<tr><td align="center"> 2    </td><td align="center"> 32x32  </td><td align="center"> 32x16      </td><td align="center"> 16x32   </td></tr>
+<tr><td align="center"> 3    </td><td align="center"> 64x64  </td><td align="center"> 64x32      </td><td align="center"> 32x64   </td></tr>
+</tbody></table>
+<a class="header" href="#objectattributesattr2" id="objectattributesattr2"><h3>ObjectAttributes.attr2</h3></a>
+<ul>
+<li>10 bits for the base tile index</li>
+<li>2 bits for priority</li>
+<li>4 bits for the palbank index (4bpp mode only, ignored in 8bpp)</li>
+</ul>
+<a class="header" href="#objectattributes-summary" id="objectattributes-summary"><h3>ObjectAttributes summary</h3></a>
+<p>So I said in the GBA memory mapping section that C people would tell you that
+the object attributes should look like this:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+#[repr(C)]
+pub struct ObjectAttributes {
+  attr0: u16,
+  attr1: u16,
+  attr2: u16,
+  filler: i16,
+}
+#}</code></pre></pre>
+<p>Except that:</p>
+<ol>
+<li>It's wasteful when we store object attributes on their own outside of OAM
+(which we definitely might want to do).</li>
+<li>In Rust we can't access just one field through a volatile pointer (our
+pointers aren't actually volatile to begin with, just the ops we do with them
+are). We have to read or write the whole pointer's value at a time.
+Similarly, we can't do things like <code>|=</code> and <code>&amp;=</code> with volatile in Rust. So in
+rust we can't have a volatile pointer to an ObjectAttributes and then write
+to just the three &quot;real&quot; values and not touch the filler field. Having the
+filler value in there just means we have to dance around it more, not less.</li>
+<li>We want to newtype this whole thing to prevent accidental invalid states from
+being written into memory.</li>
+</ol>
+<p>So we will not be using that representation. At the same time we want to have no
+overhead, so we will stick to three <code>u16</code> values. We could newtype each
+individual field to be its own type (<code>ObjectAttributesAttr0</code> or something silly
+like that), since there aren't actual dependencies between two different fields
+such that a change in one can throw another into a forbidden state. The worst
+that can happen is if we disable or enable affine mode (<code>attr0</code>) it can change
+the meaning of <code>attr1</code>. The changed meaning isn't actually in invalid state
+though, so we <em>could</em> make each field its own type if we wanted.</p>
+<p>However, when you think about it, I can't imagine a common situation where we do
+something like make an <code>attr0</code> value that we then want to save on its own and
+apply to several different <code>ObjectAttributes</code> that we make during a game. That
+just doesn't sound likely to me. So, we'll go the route where <code>ObjectAttributes</code>
+is just a big black box to the outside world and we don't need to think about
+the three fields internally as being separate.</p>
+<p>First we make it so that we can get and set object attributes from memory:</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+pub const OAM: usize = 0x700_0000;
+
+pub fn object_attributes(slot: usize) -&gt; ObjectAttributes {
+  assert!(slot &lt; 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::&lt;u16&gt;() * 4)) as *mut u16);
+  unsafe {
+    ObjectAttributes {
+      attr0: ptr.read(),
+      attr1: ptr.offset(1).read(),
+      attr2: ptr.offset(2).read(),
+    }
+  }
+}
+
+pub fn set_object_attributes(slot: usize, obj: ObjectAttributes) {
+  assert!(slot &lt; 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::&lt;u16&gt;() * 4)) as *mut u16);
+  unsafe {
+    ptr.write(obj.attr0);
+    ptr.offset(1).write(obj.attr1);
+    ptr.offset(2).write(obj.attr2);
+  }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct ObjectAttributes {
+  attr0: u16,
+  attr1: u16,
+  attr2: u16,
+}
+#}</code></pre></pre>
+<p>Then we add a billion methods to the <code>ObjectAttributes</code> type so that we can
+actually set all the different values that we want to set.</p>
+<p>This code block is the last thing on this page so if you don't wanna scroll past
+the whole thing you can just go to the next page.</p>
+<pre><pre class="playpen"><code class="language-rust">
+# #![allow(unused_variables)]
+#fn main() {
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectRenderMode {
+  Normal,
+  Affine,
+  Disabled,
+  DoubleAreaAffine,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectMode {
+  Normal,
+  AlphaBlending,
+  ObjectWindow,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectShape {
+  Square,
+  Horizontal,
+  Vertical,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectOrientation {
+  Normal,
+  HFlip,
+  VFlip,
+  BothFlip,
+  Affine(u8),
+}
+
+impl ObjectAttributes {
+  pub fn row(&amp;self) -&gt; u16 {
+    self.attr0 &amp; 0b1111_1111
+  }
+  pub fn column(&amp;self) -&gt; u16 {
+    self.attr1 &amp; 0b1_1111_1111
+  }
+  pub fn rendering(&amp;self) -&gt; ObjectRenderMode {
+    match (self.attr0 &gt;&gt; 8) &amp; 0b11 {
+      0 =&gt; ObjectRenderMode::Normal,
+      1 =&gt; ObjectRenderMode::Affine,
+      2 =&gt; ObjectRenderMode::Disabled,
+      3 =&gt; ObjectRenderMode::DoubleAreaAffine,
+      _ =&gt; unimplemented!(),
+    }
+  }
+  pub fn mode(&amp;self) -&gt; ObjectMode {
+    match (self.attr0 &gt;&gt; 0xA) &amp; 0b11 {
+      0 =&gt; ObjectMode::Normal,
+      1 =&gt; ObjectMode::AlphaBlending,
+      2 =&gt; ObjectMode::ObjectWindow,
+      _ =&gt; unimplemented!(),
+    }
+  }
+  pub fn mosaic(&amp;self) -&gt; bool {
+    ((self.attr0 &lt;&lt; 3) as i16) &lt; 0
+  }
+  pub fn two_fifty_six_colors(&amp;self) -&gt; bool {
+    ((self.attr0 &lt;&lt; 2) as i16) &lt; 0
+  }
+  pub fn shape(&amp;self) -&gt; ObjectShape {
+    match (self.attr0 &gt;&gt; 0xE) &amp; 0b11 {
+      0 =&gt; ObjectShape::Square,
+      1 =&gt; ObjectShape::Horizontal,
+      2 =&gt; ObjectShape::Vertical,
+      _ =&gt; unimplemented!(),
+    }
+  }
+  pub fn orientation(&amp;self) -&gt; ObjectOrientation {
+    if (self.attr0 &gt;&gt; 8) &amp; 1 &gt; 0 {
+      ObjectOrientation::Affine((self.attr1 &gt;&gt; 9) as u8 &amp; 0b1_1111)
+    } else {
+      match (self.attr1 &gt;&gt; 0xC) &amp; 0b11 {
+        0 =&gt; ObjectOrientation::Normal,
+        1 =&gt; ObjectOrientation::HFlip,
+        2 =&gt; ObjectOrientation::VFlip,
+        3 =&gt; ObjectOrientation::BothFlip,
+      }
+    }
+  }
+  pub fn size(&amp;self) -&gt; u16 {
+    self.attr1 &gt;&gt; 0xE
+  }
+  pub fn tile_index(&amp;self) -&gt; u16 {
+    self.attr2 &amp; 0b11_1111_1111
+  }
+  pub fn priority(&amp;self) -&gt; u16 {
+    self.attr2 &gt;&gt; 0xA
+  }
+  pub fn palbank(&amp;self) -&gt; u16 {
+    self.attr2 &gt;&gt; 0xC
+  }
+  //
+  pub fn set_row(&amp;mut self, row: u16) {
+    self.attr0 &amp;= !0b1111_1111;
+    self.attr0 |= row &amp; 0b1111_1111;
+  }
+  pub fn set_column(&amp;mut self, col: u16) {
+    self.attr1 &amp;= !0b1_1111_1111;
+    self.attr2 |= col &amp; 0b1_1111_1111;
+  }
+  pub fn set_rendering(&amp;mut self, rendering: ObjectRenderMode) {
+    const RENDERING_MASK: u16 = 0b11 &lt;&lt; 8;
+    self.attr0 &amp;= !RENDERING_MASK;
+    self.attr0 |= (rendering as u16) &lt;&lt; 8;
+  }
+  pub fn set_mode(&amp;mut self, mode: ObjectMode) {
+    const MODE_MASK: u16 = 0b11 &lt;&lt; 0xA;
+    self.attr0 &amp;= MODE_MASK;
+    self.attr0 |= (mode as u16) &lt;&lt; 0xA;
+  }
+  pub fn set_mosaic(&amp;mut self, bit: bool) {
+    const MOSAIC_BIT: u16 = 1 &lt;&lt; 0xC;
+    if bit {
+      self.attr0 |= MOSAIC_BIT
+    } else {
+      self.attr0 &amp;= !MOSAIC_BIT
+    }
+  }
+  pub fn set_two_fifty_six_colors(&amp;mut self, bit: bool) {
+    const COLOR_MODE_BIT: u16 = 1 &lt;&lt; 0xD;
+    if bit {
+      self.attr0 |= COLOR_MODE_BIT
+    } else {
+      self.attr0 &amp;= !COLOR_MODE_BIT
+    }
+  }
+  pub fn set_shape(&amp;mut self, shape: ObjectShape) {
+    self.attr0 &amp;= 0b0011_1111_1111_1111;
+    self.attr0 |= (shape as u16) &lt;&lt; 0xE;
+  }
+  pub fn set_orientation(&amp;mut self, orientation: ObjectOrientation) {
+    const AFFINE_INDEX_MASK: u16 = 0b1_1111 &lt;&lt; 9;
+    self.attr1 &amp;= !AFFINE_INDEX_MASK;
+    let bits = match orientation {
+      ObjectOrientation::Affine(index) =&gt; (index as u16) &lt;&lt; 9,
+      ObjectOrientation::Normal =&gt; 0,
+      ObjectOrientation::HFlip =&gt; 1 &lt;&lt; 0xC,
+      ObjectOrientation::VFlip =&gt; 1 &lt;&lt; 0xD,
+      ObjectOrientation::BothFlip =&gt; 0b11 &lt;&lt; 0xC,
+    };
+    self.attr1 |= bits;
+  }
+  pub fn set_size(&amp;mut self, size: u16) {
+    self.attr1 &amp;= 0b0011_1111_1111_1111;
+    self.attr1 |= size &lt;&lt; 14;
+  }
+  pub fn set_tile_index(&amp;mut self, index: u16) {
+    self.attr2 &amp;= !0b11_1111_1111;
+    self.attr2 |= 0b11_1111_1111 &amp; index;
+  }
+  pub fn set_priority(&amp;mut self, priority: u16) {
+    self.attr2 &amp;= !0b0000_1100_0000_0000;
+    self.attr2 |= (priority &amp; 0b11) &lt;&lt; 0xA;
+  }
+  pub fn set_palbank(&amp;mut self, palbank: u16) {
+    self.attr2 &amp;= !0b1111_0000_0000_0000;
+    self.attr2 |= (palbank &amp; 0b1111) &lt;&lt; 0xC;
+  }
+}
+#}</code></pre></pre>
 <a class="header" href="#gba-rng" id="gba-rng"><h1>GBA RNG</h1></a>
 <p>TODO</p>
 <a class="header" href="#memory_game" id="memory_game"><h1>memory_game</h1></a>

examples/memory_game.rs

@@ -286,3 +286,208 @@ impl RegularScreenblockEntry {
     self.0 |= palbank_index;
   }
 }
+
+pub const PALRAM_OBJECT_BASE: VolatilePtr<u16> = VolatilePtr(0x500_0200 as *mut u16);
+
+pub fn object_palette(slot: usize) -> u16 {
+  assert!(slot < 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).read() }
+}
+
+pub fn set_object_palette(slot: usize, color: u16) {
+  assert!(slot < 256);
+  unsafe { PALRAM_OBJECT_BASE.offset(slot as isize).write(color) }
+}
+
+pub const OAM: usize = 0x700_0000;
+
+pub fn object_attributes(slot: usize) -> ObjectAttributes {
+  assert!(slot < 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::<u16>() * 4)) as *mut u16);
+  unsafe {
+    ObjectAttributes {
+      attr0: ptr.read(),
+      attr1: ptr.offset(1).read(),
+      attr2: ptr.offset(2).read(),
+    }
+  }
+}
+
+pub fn set_object_attributes(slot: usize, obj: ObjectAttributes) {
+  assert!(slot < 128);
+  let ptr = VolatilePtr((OAM + slot * (size_of::<u16>() * 4)) as *mut u16);
+  unsafe {
+    ptr.write(obj.attr0);
+    ptr.offset(1).write(obj.attr1);
+    ptr.offset(2).write(obj.attr2);
+  }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct ObjectAttributes {
+  attr0: u16,
+  attr1: u16,
+  attr2: u16,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectRenderMode {
+  Normal,
+  Affine,
+  Disabled,
+  DoubleAreaAffine,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectMode {
+  Normal,
+  AlphaBlending,
+  ObjectWindow,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectShape {
+  Square,
+  Horizontal,
+  Vertical,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ObjectOrientation {
+  Normal,
+  HFlip,
+  VFlip,
+  BothFlip,
+  Affine(u8),
+}
+
+impl ObjectAttributes {
+  pub fn row(&self) -> u16 {
+    self.attr0 & 0b1111_1111
+  }
+  pub fn column(&self) -> u16 {
+    self.attr1 & 0b1_1111_1111
+  }
+  pub fn rendering(&self) -> ObjectRenderMode {
+    match (self.attr0 >> 8) & 0b11 {
+      0 => ObjectRenderMode::Normal,
+      1 => ObjectRenderMode::Affine,
+      2 => ObjectRenderMode::Disabled,
+      3 => ObjectRenderMode::DoubleAreaAffine,
+      _ => unimplemented!(),
+    }
+  }
+  pub fn mode(&self) -> ObjectMode {
+    match (self.attr0 >> 0xA) & 0b11 {
+      0 => ObjectMode::Normal,
+      1 => ObjectMode::AlphaBlending,
+      2 => ObjectMode::ObjectWindow,
+      _ => unimplemented!(),
+    }
+  }
+  pub fn mosaic(&self) -> bool {
+    ((self.attr0 << 3) as i16) < 0
+  }
+  pub fn two_fifty_six_colors(&self) -> bool {
+    ((self.attr0 << 2) as i16) < 0
+  }
+  pub fn shape(&self) -> ObjectShape {
+    match (self.attr0 >> 0xE) & 0b11 {
+      0 => ObjectShape::Square,
+      1 => ObjectShape::Horizontal,
+      2 => ObjectShape::Vertical,
+      _ => unimplemented!(),
+    }
+  }
+  pub fn orientation(&self) -> ObjectOrientation {
+    if (self.attr0 >> 8) & 1 > 0 {
+      ObjectOrientation::Affine((self.attr1 >> 9) as u8 & 0b1_1111)
+    } else {
+      match (self.attr1 >> 0xC) & 0b11 {
+        0 => ObjectOrientation::Normal,
+        1 => ObjectOrientation::HFlip,
+        2 => ObjectOrientation::VFlip,
+        3 => ObjectOrientation::BothFlip,
+      }
+    }
+  }
+  pub fn size(&self) -> u16 {
+    self.attr1 >> 0xE
+  }
+  pub fn tile_index(&self) -> u16 {
+    self.attr2 & 0b11_1111_1111
+  }
+  pub fn priority(&self) -> u16 {
+    self.attr2 >> 0xA
+  }
+  pub fn palbank(&self) -> u16 {
+    self.attr2 >> 0xC
+  }
+  //
+  pub fn set_row(&mut self, row: u16) {
+    self.attr0 &= !0b1111_1111;
+    self.attr0 |= row & 0b1111_1111;
+  }
+  pub fn set_column(&mut self, col: u16) {
+    self.attr1 &= !0b1_1111_1111;
+    self.attr2 |= col & 0b1_1111_1111;
+  }
+  pub fn set_rendering(&mut self, rendering: ObjectRenderMode) {
+    const RENDERING_MASK: u16 = 0b11 << 8;
+    self.attr0 &= !RENDERING_MASK;
+    self.attr0 |= (rendering as u16) << 8;
+  }
+  pub fn set_mode(&mut self, mode: ObjectMode) {
+    const MODE_MASK: u16 = 0b11 << 0xA;
+    self.attr0 &= MODE_MASK;
+    self.attr0 |= (mode as u16) << 0xA;
+  }
+  pub fn set_mosaic(&mut self, bit: bool) {
+    const MOSAIC_BIT: u16 = 1 << 0xC;
+    if bit {
+      self.attr0 |= MOSAIC_BIT
+    } else {
+      self.attr0 &= !MOSAIC_BIT
+    }
+  }
+  pub fn set_two_fifty_six_colors(&mut self, bit: bool) {
+    const COLOR_MODE_BIT: u16 = 1 << 0xD;
+    if bit {
+      self.attr0 |= COLOR_MODE_BIT
+    } else {
+      self.attr0 &= !COLOR_MODE_BIT
+    }
+  }
+  pub fn set_shape(&mut self, shape: ObjectShape) {
+    self.attr0 &= 0b0011_1111_1111_1111;
+    self.attr0 |= (shape as u16) << 0xE;
+  }
+  pub fn set_orientation(&mut self, orientation: ObjectOrientation) {
+    const AFFINE_INDEX_MASK: u16 = 0b1_1111 << 9;
+    self.attr1 &= !AFFINE_INDEX_MASK;
+    let bits = match orientation {
+      ObjectOrientation::Affine(index) => (index as u16) << 9,
+      ObjectOrientation::Normal => 0,
+      ObjectOrientation::HFlip => 1 << 0xC,
+      ObjectOrientation::VFlip => 1 << 0xD,
+      ObjectOrientation::BothFlip => 0b11 << 0xC,
+    };
+    self.attr1 |= bits;
+  }
+  pub fn set_size(&mut self, size: u16) {
+    self.attr1 &= 0b0011_1111_1111_1111;
+    self.attr1 |= size << 14;
+  }
+  pub fn set_tile_index(&mut self, index: u16) {
+    self.attr2 &= !0b11_1111_1111;
+    self.attr2 |= 0b11_1111_1111 & index;
+  }
+  pub fn set_priority(&mut self, priority: u16) {
+    self.attr2 &= !0b0000_1100_0000_0000;
+    self.attr2 |= (priority & 0b11) << 0xA;
+  }
+  pub fn set_palbank(&mut self, palbank: u16) {
+    self.attr2 &= !0b1111_0000_0000_0000;
+    self.attr2 |= (palbank & 0b1111) << 0xC;
+  }
+}