Nicer test logo (#707)

With the new examples page on the website, I thought it was probably
time to update the logo we use there to a nicer one.

I've also added a basic one to make the background colour change example
nicer, and sometimes you might want the less busy one.

- [x] Changelog updated

![image](https://github.com/agbrs/agb/assets/460842/062bb473-1b2f-4db0-a712-6d264240be9a)

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Added `find_colour_index_16` and `find_colour_index_256` to the `VRamManager` to find where a colour is in a palette.
+
 ## [0.20.2] - 2024/05/25
 
 ### Fixed

agb/examples/dma_effect_background_colour.rs

@@ -25,24 +25,25 @@ fn main(mut gba: agb::Gba) -> ! {
 
     let dma = gba.dma.dma().dma0;
 
-    example_logo::display_logo(&mut map, &mut vram);
+    example_logo::display_logo_basic(&mut map, &mut vram);
 
     let vblank = VBlank::get();
 
     let colours: Box<[_]> = (0..160).map(|i| ((i * 0xffff) / 160) as u16).collect();
 
-    let mut frame = 0;
+    let background_colour = 0x732b; // generated using `https://agbrs.dev/colour`
+    let background_colour_index = vram
+        .find_colour_index_16(0, background_colour)
+        .expect("Should contain colour 0x732b");
 
     loop {
-        // hardcoding palette index 2 here which you wouldn't want to do in a real example (instead, look for
-        // the colour you want to replace)
-        let _background_color_transfer =
-            unsafe { dma.hblank_transfer(&vram.background_palette_colour_dma(0, 2), &colours) };
+        let _background_color_transfer = unsafe {
+            dma.hblank_transfer(
+                &vram.background_palette_colour_dma(0, background_colour_index),
+                &colours,
+            )
+        };
 
         vblank.wait_for_vblank();
-        frame += 1;
-        if frame > 160 {
-            frame = 0;
-        }
     }
 }

agb/src/display/example_logo.rs

@@ -1,6 +1,7 @@
 use super::tiled::{RegularMap, TiledMap, VRamManager};
 
 crate::include_background_gfx!(crate, agb_logo, test_logo => deduplicate "gfx/test_logo.png");
+crate::include_background_gfx!(crate, agb_logo_basic, test_logo => deduplicate "gfx/test_logo_basic.png");
 
 pub fn display_logo(map: &mut RegularMap, vram: &mut VRamManager) {
     vram.set_background_palettes(agb_logo::PALETTES);
@@ -11,6 +12,15 @@ pub fn display_logo(map: &mut RegularMap, vram: &mut VRamManager) {
     map.set_visible(true);
 }
 
+pub fn display_logo_basic(map: &mut RegularMap, vram: &mut VRamManager) {
+    vram.set_background_palettes(agb_logo_basic::PALETTES);
+
+    map.fill_with(vram, &agb_logo_basic::test_logo);
+
+    map.commit(vram);
+    map.set_visible(true);
+}
+
 #[cfg(test)]
 mod tests {
     use crate::display::{tiled::RegularBackgroundSize, Priority};

agb/src/display/tiled/vram_manager.rs

@@ -461,4 +461,18 @@ impl VRamManager {
             self.set_background_palette(palette_index as u8, entry);
         }
     }
+
+    /// Gets the index of the colour for a given background palette, or None if it doesn't exist
+    #[must_use]
+    pub fn find_colour_index_16(&self, palette_index: usize, colour: u16) -> Option<usize> {
+        assert!(palette_index < 16);
+
+        (0..16).find(|i| PALETTE_BACKGROUND.get(palette_index * 16 + i) == colour)
+    }
+
+    /// Gets the index of the colour in the entire background palette, or None if it doesn't exist
+    #[must_use]
+    pub fn find_colour_index_256(&self, colour: u16) -> Option<usize> {
+        (0..256).find(|&i| PALETTE_BACKGROUND.get(i) == colour)
+    }
 }