diff --git a/README.md b/README.md
index 3d55f45a3648454fdb995aab486e1cf959fbe27c..784a120a2b52f288703db581240b0fc63d66117b 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@ A Game Boy emulator that is written in Rust 🦀.
* Game Boy Printer emulation
* Support for multiple MBCs: MBC1, MBC2, MBC3, and MBC5
* Variable CPU clock speed
-* Accurate PPU - passes [dmg-acid2](https://github.com/mattcurrie/dmg-acid2) tests
+* Accurate PPU - passes [dmg-acid2](https://github.com/mattcurrie/dmg-acid2) and [cgb-acid2](https://github.com/mattcurrie/cgb-acid2) tests
For the Web front-end...
diff --git a/frontends/sdl/res/test/cgb_acid2.png b/frontends/sdl/res/test/cgb_acid2.png
new file mode 100644
index 0000000000000000000000000000000000000000..6d23ed4468bb4e3fc45019b1ac6fb7aea4642067
Binary files /dev/null and b/frontends/sdl/res/test/cgb_acid2.png differ
diff --git a/frontends/sdl/src/test.rs b/frontends/sdl/src/test.rs
index 154a5a34c8b8a7d4588d2ee48451d1f2d0d86765..7fa014f81ad9c1f2ce1eb6f7407d0bd5848157a4 100644
--- a/frontends/sdl/src/test.rs
+++ b/frontends/sdl/src/test.rs
@@ -26,6 +26,7 @@ pub fn compare_images(source_pixels: &[u8], target_path: &str) -> bool {
#[cfg(test)]
mod tests {
use boytacean::{
+ gb::GameBoyMode,
ppu::FRAME_BUFFER_SIZE,
test::{run_image_test, TestOptions},
};
@@ -54,6 +55,20 @@ mod tests {
assert_eq!(image_result, true);
}
+ #[test]
+ fn test_cgb_acid2() {
+ let result: [u8; FRAME_BUFFER_SIZE] = run_image_test(
+ "../../res/roms/test/cgb_acid2.gbc",
+ Some(50000000),
+ TestOptions {
+ mode: Some(GameBoyMode::Cgb),
+ ..Default::default()
+ },
+ );
+ let image_result = compare_images(&result, "res/test/cgb_acid2.png");
+ assert_eq!(image_result, true);
+ }
+
#[test]
fn test_firstwhite() {
let result: [u8; FRAME_BUFFER_SIZE] = run_image_test(
diff --git a/src/ppu.rs b/src/ppu.rs
index 9e20dffeb1bfcdf3821973eb25e004381ca8201c..24fbe4f586997718d8b8fbbb9d2d1cf41ba37ae2 100644
--- a/src/ppu.rs
+++ b/src/ppu.rs
@@ -285,6 +285,11 @@ pub struct Ppu {
/// processed set of pixels ready to be displayed on screen.
pub frame_buffer: Box<[u8; FRAME_BUFFER_SIZE]>,
+ /// The buffer that will control the background to OAM
+ /// priority, allowing the background to be drawn over
+ /// the sprites/objects if necessary.
+ priority_buffer: Box<[bool; COLOR_BUFFER_SIZE]>,
+
/// Video dedicated memory (VRAM) where both the tiles and
/// the sprites/objects are going to be stored.
vram: [u8; VRAM_SIZE],
@@ -499,6 +504,7 @@ impl Ppu {
Self {
color_buffer: Box::new([0u8; COLOR_BUFFER_SIZE]),
frame_buffer: Box::new([0u8; FRAME_BUFFER_SIZE]),
+ priority_buffer: Box::new([false; COLOR_BUFFER_SIZE]),
vram: [0u8; VRAM_SIZE],
hram: [0u8; HRAM_SIZE],
oam: [0u8; OAM_SIZE],
@@ -555,6 +561,7 @@ impl Ppu {
pub fn reset(&mut self) {
self.color_buffer = Box::new([0u8; COLOR_BUFFER_SIZE]);
self.frame_buffer = Box::new([0u8; FRAME_BUFFER_SIZE]);
+ self.priority_buffer = Box::new([false; COLOR_BUFFER_SIZE]);
self.vram = [0u8; VRAM_SIZE_CGB];
self.hram = [0u8; HRAM_SIZE];
self.vram_bank = 0x0;
@@ -1196,6 +1203,10 @@ impl Ppu {
let mut xflip = tile_attr.xflip;
let mut yflip = tile_attr.yflip;
+ // obtains the value the BG-to-OAM priority to be used in the computation
+ // of the final pixel value (CGB only)
+ let mut priority = tile_attr.priority;
+
// increments the tile index value by the required offset for the VRAM
// bank in which the tile is stored, this is only required for CGB mode
tile_index += tile_attr.vram_bank as usize * TILE_COUNT_DMG;
@@ -1240,6 +1251,12 @@ impl Ppu {
self.frame_buffer[frame_offset + 1] = color[1];
self.frame_buffer[frame_offset + 2] = color[2];
+ // updates the priority buffer with the current pixel
+ // the priority is only set in case the priority of
+ // the background (over OAM) is set in the attributes
+ // and the pixel is not transparent
+ self.priority_buffer[color_offset] = priority && pixel > 0;
+
// increments the current tile X position in drawing
x += 1;
@@ -1269,6 +1286,7 @@ impl Ppu {
palette = &self.palettes_color_bg[tile_attr.palette as usize];
xflip = tile_attr.xflip;
yflip = tile_attr.yflip;
+ priority = tile_attr.priority;
tile_index += tile_attr.vram_bank as usize * TILE_COUNT_DMG;
}
@@ -1540,7 +1558,13 @@ impl Ppu {
// window should be drawn over or if the underlying pixel
// is transparent (zero value) meaning there's no background
// or window for the provided pixel
- let is_visible = obj_over || self.color_buffer[color_offset as usize] == 0;
+ let mut is_visible = obj_over || self.color_buffer[color_offset as usize] == 0;
+
+ // additionally (in CCG mode) the object is only considered to
+ // be visible if the priority buffer is not set for the current
+ // pixel, this means that the background is capturing priority
+ // by having the BG-to-OAM priority bit set in the bg map attributes
+ is_visible &= always_over || !self.priority_buffer[color_offset as usize];
// determines if the current pixel has priority over a possible
// one that has been drawn by a previous object, this happens
diff --git a/src/test.rs b/src/test.rs
index c9e0369833c85c1896cf792d17774dfc5dcfa78b..ac1cd49725defdab96b01ecaec1e4aad15eaa0b5 100644
--- a/src/test.rs
+++ b/src/test.rs
@@ -1,16 +1,21 @@
-use crate::{devices::buffer::BufferDevice, gb::GameBoy, ppu::FRAME_BUFFER_SIZE};
+use crate::{
+ devices::buffer::BufferDevice,
+ gb::{GameBoy, GameBoyMode},
+ ppu::FRAME_BUFFER_SIZE,
+};
#[derive(Default)]
pub struct TestOptions {
- ppu_enabled: Option<bool>,
- apu_enabled: Option<bool>,
- dma_enabled: Option<bool>,
- timer_enabled: Option<bool>,
+ pub mode: Option<GameBoyMode>,
+ pub ppu_enabled: Option<bool>,
+ pub apu_enabled: Option<bool>,
+ pub dma_enabled: Option<bool>,
+ pub timer_enabled: Option<bool>,
}
pub fn build_test(options: TestOptions) -> GameBoy {
let device = Box::<BufferDevice>::default();
- let mut game_boy = GameBoy::new(None);
+ let mut game_boy = GameBoy::new(options.mode);
game_boy.set_ppu_enabled(options.ppu_enabled.unwrap_or(true));
game_boy.set_apu_enabled(options.apu_enabled.unwrap_or(true));
game_boy.set_dma_enabled(options.dma_enabled.unwrap_or(true));