feat: implement brightness increase/decrease

src/ppu.zig

@@ -164,7 +164,7 @@ pub const Ppu = struct {
             const x = (sprite.x() +% i) % width;
             const ix = @bitCast(i9, x);
 
-            if (self.scanline.top()[x] != null) continue;
+            if (!shouldDrawSprite(self.bldcnt, &self.scanline, x)) continue;
 
             const sprite_start = sprite.x();
             const isprite_start = @bitCast(i9, sprite_start);
@@ -191,7 +191,10 @@ pub const Ppu = struct {
             const pal_id: u16 = if (!is_8bpp) get4bppTilePalette(sprite.palBank(), col, tile) else tile;
 
             // Sprite Palette starts at 0x0500_0200
-            if (pal_id != 0) self.scanline.top()[x] = self.palette.read(u16, 0x200 + pal_id * 2);
+            if (pal_id != 0) {
+                const bgr555 = self.palette.read(u16, 0x200 + pal_id * 2);
+                copyToSpriteBuffer(self.bldcnt, &self.scanline, x, bgr555);
+            }
         }
     }
 
@@ -211,15 +214,7 @@ pub const Ppu = struct {
             const x = (sprite.x() +% i) % width;
             const ix = @bitCast(i9, x);
 
-            if (self.scanline.top()[x] != null) continue;
-
-            if (self.scanline.btm()[x] != null) {
-                if (self.bldcnt.mode.read() != 0b01) continue;
-
-                const b_layers = self.bldcnt.layer_b.read();
-                const is_blend_enabled = (b_layers >> 4) & 1 == 1;
-                if (!is_blend_enabled) continue;
-            }
+            if (!shouldDrawSprite(self.bldcnt, &self.scanline, x)) continue;
 
             const sprite_start = sprite.x();
             const isprite_start = @bitCast(i9, sprite_start);
@@ -254,19 +249,7 @@ pub const Ppu = struct {
             // Sprite Palette starts at 0x0500_0200
             if (pal_id != 0) {
                 const bgr555 = self.palette.read(u16, 0x200 + pal_id * 2);
-
-                if (self.bldcnt.mode.read() == 0b01) {
-                    // Alpha Blending
-                    const a_layers = self.bldcnt.layer_a.read();
-                    const is_blend_enabled = (a_layers >> 4) & 1 == 1;
-
-                    if (is_blend_enabled) {
-                        self.scanline.btm()[x] = bgr555;
-                        return;
-                    }
-                }
-
-                self.scanline.top()[x] = bgr555;
+                copyToSpriteBuffer(self.bldcnt, &self.scanline, x, bgr555);
             }
         }
     }
@@ -312,7 +295,7 @@ pub const Ppu = struct {
 
             if (pal_id != 0) {
                 const bgr555 = self.palette.read(u16, pal_id * 2);
-                drawToScanlineBuffer(n, self.bldcnt, &self.scanline, i, bgr555);
+                copyToBackgroundBuffer(n, self.bldcnt, &self.scanline, i, bgr555);
             }
         }
 
@@ -369,7 +352,7 @@ pub const Ppu = struct {
 
             if (pal_id != 0) {
                 const bgr555 = self.palette.read(u16, pal_id * 2);
-                drawToScanlineBuffer(n, self.bldcnt, &self.scanline, i, bgr555);
+                copyToBackgroundBuffer(n, self.bldcnt, &self.scanline, i, bgr555);
             }
         }
     }
@@ -407,8 +390,7 @@ pub const Ppu = struct {
                     const maybe_top = maybe_px;
                     const maybe_btm = self.scanline.btm()[i];
 
-                    // TODO: Why must I reverse this?
-                    const bgr555 = getBgr555(&self.palette, self.bldalpha, maybe_btm, maybe_top);
+                    const bgr555 = self.getBgr555(maybe_top, maybe_btm);
                     std.mem.writeIntNative(u32, self.framebuf.get(.Emulator)[fb_base + i * @sizeOf(u32) ..][0..@sizeOf(u32)], COLOUR_LUT[bgr555 & 0x7FFF]);
                 }
 
@@ -435,8 +417,7 @@ pub const Ppu = struct {
                     const maybe_top = maybe_px;
                     const maybe_btm = self.scanline.btm()[i];
 
-                    // TODO: Why must I reverse this?
-                    const bgr555 = getBgr555(&self.palette, self.bldalpha, maybe_btm, maybe_top);
+                    const bgr555 = self.getBgr555(maybe_top, maybe_btm);
                     std.mem.writeIntNative(u32, self.framebuf.get(.Emulator)[fb_base + i * @sizeOf(u32) ..][0..@sizeOf(u32)], COLOUR_LUT[bgr555 & 0x7FFF]);
                 }
 
@@ -462,8 +443,7 @@ pub const Ppu = struct {
                     const maybe_top = maybe_px;
                     const maybe_btm = self.scanline.btm()[i];
 
-                    // TODO: Why must I reverse this?
-                    const bgr555 = getBgr555(&self.palette, self.bldalpha, maybe_btm, maybe_top);
+                    const bgr555 = self.getBgr555(maybe_top, maybe_btm);
                     std.mem.writeIntNative(u32, self.framebuf.get(.Emulator)[fb_base + i * @sizeOf(u32) ..][0..@sizeOf(u32)], COLOUR_LUT[bgr555 & 0x7FFF]);
                 }
 
@@ -514,6 +494,44 @@ pub const Ppu = struct {
         }
     }
 
+    fn getBgr555(self: *Self, maybe_top: ?u16, maybe_btm: ?u16) u16 {
+        if (maybe_btm) |btm| {
+            return switch (self.bldcnt.mode.read()) {
+                0b00 => if (maybe_top) |top| top else btm,
+                0b01 => if (maybe_top) |top| alphaBlend(btm, top, self.bldalpha) else btm,
+                0b10 => blk: {
+                    const evy: u16 = self.bldy.evy.read();
+
+                    const r = btm & 0x1F;
+                    const g = (btm >> 5) & 0x1F;
+                    const b = (btm >> 10) & 0x1F;
+
+                    const bld_r = r + (((31 - r) * evy) >> 4);
+                    const bld_g = g + (((31 - g) * evy) >> 4);
+                    const bld_b = b + (((31 - b) * evy) >> 4);
+
+                    break :blk (bld_b << 10) | (bld_g << 5) | bld_r;
+                },
+                0b11 => blk: {
+                    const evy: u16 = self.bldy.evy.read();
+
+                    const btm_r = btm & 0x1F;
+                    const btm_g = (btm >> 5) & 0x1F;
+                    const btm_b = (btm >> 10) & 0x1F;
+
+                    const bld_r = btm_r - ((btm_r * evy) >> 4);
+                    const bld_g = btm_g - ((btm_g * evy) >> 4);
+                    const bld_b = btm_b - ((btm_b * evy) >> 4);
+
+                    break :blk (bld_b << 10) | (bld_g << 5) | bld_r;
+                },
+            };
+        }
+
+        if (maybe_top) |top| return top;
+        return self.palette.getBackdrop();
+    }
+
     // TODO: Comment this + get a better understanding
     fn tilemapOffset(size: u2, x: u32, y: u32) u32 {
         // Current Row: (y % PIXEL_COUNT) / 8
@@ -1050,16 +1068,6 @@ fn toRgba8888Talarubi(bgr555: u16) u32 {
     return @floatToInt(u32, out_r) << 24 | @floatToInt(u32, out_g) << 16 | @floatToInt(u32, out_b) << 8 | 0xFF;
 }
 
-fn getBgr555(palette: *const Palette, bldalpha: io.BldAlpha, maybe_top: ?u16, maybe_btm: ?u16) u16 {
-    if (maybe_top) |top| {
-        if (maybe_btm) |btm| return alphaBlend(top, btm, bldalpha);
-        return top;
-    }
-
-    if (maybe_btm) |btm| return btm;
-    return palette.getBackdrop();
-}
-
 fn alphaBlend(top: u16, btm: u16, bldalpha: io.BldAlpha) u16 {
     const eva: u16 = bldalpha.eva.read();
     const evb: u16 = bldalpha.evb.read();
@@ -1110,8 +1118,22 @@ fn shouldDrawBackground(comptime n: u2, bldcnt: io.BldCnt, scanline: *Scanline,
     return true;
 }
 
-fn drawToScanlineBuffer(comptime n: u2, bldcnt: io.BldCnt, scanline: *Scanline, i: usize, bgr555: u16) void {
-    if (bldcnt.mode.read() == 0b01) {
+fn shouldDrawSprite(bldcnt: io.BldCnt, scanline: *Scanline, x: u9) bool {
+    if (scanline.top()[x] != null) return false;
+
+    if (scanline.btm()[x] != null) {
+        if (bldcnt.mode.read() != 0b01) return false;
+
+        const b_layers = bldcnt.layer_b.read();
+        const is_blend_enabled = (b_layers >> 4) & 1 == 1;
+        if (!is_blend_enabled) return false;
+    }
+
+    return true;
+}
+
+fn copyToBackgroundBuffer(comptime n: u2, bldcnt: io.BldCnt, scanline: *Scanline, i: usize, bgr555: u16) void {
+    if (bldcnt.mode.read() != 0b00) {
         // Standard Alpha Blending
         const a_layers = bldcnt.layer_a.read();
         const is_blend_enabled = (a_layers >> n) & 1 == 1;
@@ -1127,6 +1149,21 @@ fn drawToScanlineBuffer(comptime n: u2, bldcnt: io.BldCnt, scanline: *Scanline,
     scanline.top()[i] = bgr555;
 }
 
+fn copyToSpriteBuffer(bldcnt: io.BldCnt, scanline: *Scanline, x: u9, bgr555: u16) void {
+    if (bldcnt.mode.read() != 0b00) {
+        // Alpha Blending
+        const a_layers = bldcnt.layer_a.read();
+        const is_blend_enabled = (a_layers >> 4) & 1 == 1;
+
+        if (is_blend_enabled) {
+            scanline.btm()[x] = bgr555;
+            return;
+        }
+    }
+
+    scanline.top()[x] = bgr555;
+}
+
 const Scanline = struct {
     const Self = @This();