iter_tiles_of_area took a surprising amount of time to write in a way that avoids duplicate lookups.

examples/game.rs

@@ -16,30 +16,46 @@ fn panic_handler(info: &core::panic::PanicInfo) -> ! {
 
 #[no_mangle]
 extern "C" fn main() -> ! {
+  // game simulation
+  let mut player_x = Wrapping(13);
+  let mut player_y = Wrapping(37);
+  let mut world = [[0_u8; 32]; 32];
+  world[0][0] = b'B';
+  world[1][0] = b'G';
+  world[2][0] = b'0';
+
+  // hardware configuration
   DISPSTAT.write(DisplayStatus::new().with_irq_vblank(true));
   IE.write(IrqBits::VBLANK);
   IME.write(true);
 
   TIMER0_CONTROL.write(TimerControl::new().with_enabled(true));
 
-  Cga8x8Thick.bitunpack_4bpp(CHARBLOCK0_4BPP.as_region(), 0);
-  Cga8x8Thick.bitunpack_4bpp(OBJ_TILES.as_region(), 0);
   BG_PALETTE.index(1).write(Color::MAGENTA);
   OBJ_PALETTE.index(1).write(Color::CYAN);
 
-  let no_display = ObjAttr0::new().with_style(ObjDisplayStyle::NotDisplayed);
-  OBJ_ATTR0.iter().for_each(|va| va.write(no_display));
+  Cga8x8Thick.bitunpack_4bpp(CHARBLOCK0_4BPP.as_region(), 0);
+  Cga8x8Thick.bitunpack_4bpp(OBJ_TILES.as_region(), 0);
 
-  let mut x = Wrapping(13);
-  let mut y = Wrapping(37);
+  BG0CNT.write(BackgroundControl::new().with_screenblock(8));
+  let screenblock_addr = TextScreenblockAddress::new(8);
+  for row in 0..32 {
+    for col in 0..32 {
+      let te = TextEntry::new().with_tile(world[row][col] as u16);
+      screenblock_addr.row_col(row, col).write(te);
+    }
+  }
 
   let mut obj = ObjAttr::new();
-  obj.set_x(x.0);
-  obj.set_y(y.0);
+  obj.set_x(player_x.0);
+  obj.set_y(player_y.0);
   obj.set_tile_id(1);
   OBJ_ATTR_ALL.index(0).write(obj);
 
-  DISPCNT.write(DisplayControl::new().with_show_obj(true));
+  let no_display = ObjAttr0::new().with_style(ObjDisplayStyle::NotDisplayed);
+  OBJ_ATTR0.iter().skip(1).for_each(|va| va.write(no_display));
+
+  DISPCNT.write(DisplayControl::new().with_show_obj(true).with_show_bg0(true));
 
   loop {
     // wait for vblank
@@ -51,18 +67,34 @@ extern "C" fn main() -> ! {
     // get input and prepare next frame
     let keys = KEYINPUT.read();
     if keys.up() {
-      y -= 1;
+      player_y -= 1;
     }
     if keys.down() {
-      y += 1;
+      player_y += 1;
     }
     if keys.left() {
-      x -= 1;
+      player_x -= 1;
     }
     if keys.right() {
-      x += 1;
+      player_x += 1;
     }
-    obj.set_x(x.0);
-    obj.set_y(y.0);
+    obj.set_x(player_x.0);
+    obj.set_y(player_y.0);
   }
 }
+
+const fn allows_movement(u: u8) -> bool {
+  u == 0 || u == b' ' || u == u8::MAX
+}
+
+fn iter_tiles_of_area(
+  (x, y): (u16, u16), (width, height): (u16, u16),
+) -> impl Iterator<Item = (u16, u16)> {
+  let y_range_incl = (y / 8)..=((y + height - 1) / 8);
+  let x_range_incl = (x / 8)..=((x + width - 1) / 8);
+  y_range_incl
+    .map(move |y_index| {
+      x_range_incl.clone().map(move |x_index| (x_index, y_index))
+    })
+    .flatten()
+}