Added chroma key support

README.md

@@ -1,4 +1,9 @@
 # GBC Input Display
 
 A lightweight input display written in Rust that can be utilized for GameBoy and GameBoy Color games.  
-This was the first Rust code I wrote, so expect it to not be very nice.
+This was the first Rust code I wrote, so expect it to not be very nice.
+
+
+# Chroma Keying
+
+The background will be drawn with +1 in the green channel, meaning that it is able to be chroma keyed out using a similarity and smoothness values of 1.

src/application.rs

@@ -164,7 +164,7 @@ pub fn draw_background() {
 
     update_dpad();
 
-    app.platform.offscreen_buffer.clear(app.palette[3]);
+    app.platform.offscreen_buffer.clear(app.palette[4]);
     for key in app.keys.iter() {
         draw!(&app.keyset, key.x, key.y, key.idx);
     }
@@ -204,7 +204,15 @@ pub fn change_palette(index: usize) {
         return;
     }
 
-    app.palette = app.palettes[index].1.clone();
+    let mut new_palette = app.palettes[index].1.clone();
+
+    // 2 palette entries are inserted:
+    //   The first one is reserved for the future
+    //   The second one is the background color + 1 green for chromakey purposes
+    new_palette.insert(3, [0, 0, 0]);
+    new_palette.insert(4, [new_palette[4][0], new_palette[4][1] + 1, new_palette[4][2]]);
+
+    app.palette = new_palette;
     app.palette_index = index;
     draw_background();
 }

src/bmp.rs

@@ -44,7 +44,7 @@ impl Index<usize> for Bitmap {
 }
 
 const BMP_SIGNATURE: u16 = 0x424d;
-const BPP: u8 = 4;
+const NUM_COLORS: u8 = 5;
 
 pub fn bmp_load(data: &[u8]) -> Result<Bitmap, BMPError> {
     let mut pointer = Cursor::new(data);
@@ -75,7 +75,7 @@ pub fn bmp_load(data: &[u8]) -> Result<Bitmap, BMPError> {
     for y in 0..header.height {
         for x in 0..header.width {
             pointer.read(&mut px)?;
-            data[(x + (header.height - y - 1) * header.width) as usize] = px[0] / (BPP << 4);
+            data[(x + (header.height - y - 1) * header.width) as usize] = px[0] / (255 / NUM_COLORS);
         }
     }