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fix: properly implement black/white blending for sprites 

There's unique rules to handle for BLDY w/r/t sprites, I didn't know
about them (shown in bld_demo.gba). I'm sure I haven't ironed out every
rule but bld_demo.gba now *actually* passes
This commit is contained in:
Rekai Nyangadzayi Musuka 2022-12-18 07:43:46 -04:00
parent 5aac04faf5
commit 0de44835e5
1 changed files with 51 additions and 29 deletions
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80
src/core/ppu.zig
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@ -725,21 +725,25 @@ pub const Ppu = struct {
fn getBgr555(self: *Self, maybe_top: Scanline.Pixel, maybe_btm: Scanline.Pixel) u16 {
return switch (self.bld.cnt.mode.read()) {
0b00 => switch (maybe_top) {
.set => |top| top,
.set, .obj_set => |top| top,
else => self.palette.backdrop(),
},
0b01 => switch (maybe_top) {
.set => |top| switch (maybe_btm) {
.set => |btm| alphaBlend(top, btm, self.bld.alpha), // ALPHA_BLEND
.set, .obj_set => |top| switch (maybe_btm) {
.set, .obj_set => |btm| alphaBlend(top, btm, self.bld.alpha), // ALPHA_BLEND
else => top,
},
else => switch (maybe_btm) {
.set => |btm| btm,
.set, .obj_set => |btm| btm,
else => self.palette.backdrop(),
},
},
0b10 => switch (maybe_btm) {
.set => |btm| blk: {
.set, .obj_set => |btm| blk: {
// If there's a top pixel + this btm pixel came from a sprite
// don't display top pixel + don't blend btm pixel
if (maybe_btm == .obj_set and maybe_top.isSet()) break :blk btm;
// BLD_WHITE
const evy: u16 = self.bld.y.evy.read();
@ -754,12 +758,16 @@ pub const Ppu = struct {
break :blk (bld_b << 10) | (bld_g << 5) | bld_r;
},
else => switch (maybe_top) {
.set => |top| top,
.set, .obj_set => |top| top,
else => self.palette.backdrop(),
},
},
0b11 => switch (maybe_btm) {
.set => |btm| blk: {
.set, .obj_set => |btm| blk: {
// If there's a top pixel + this btm pixel came from a sprite
// don't display top pixel + don't blend btm pixel
if (maybe_btm == .obj_set and maybe_top.isSet()) break :blk btm;
// BLD_BLACK
const evy: u16 = self.bld.y.evy.read();
@ -774,7 +782,7 @@ pub const Ppu = struct {
break :blk (bld_b << 10) | (bld_g << 5) | bld_r;
},
else => switch (maybe_top) {
.set => |top| top,
.set, .obj_set => |top| top,
else => self.palette.backdrop(),
},
},
@ -796,7 +804,7 @@ pub const Ppu = struct {
const is_top_layer = (top_layer >> layer) & 1 == 1;
if (is_top_layer) {
self.scanline.top()[i] = Scanline.Pixel.from(bgr555);
self.scanline.top()[i] = Scanline.Pixel.from(.Background, bgr555);
return;
}
@ -805,7 +813,7 @@ pub const Ppu = struct {
const is_btm_layer = (btm_layer >> layer) & 1 == 1;
if (is_btm_layer) {
self.scanline.btm()[i] = Scanline.Pixel.from(bgr555);
self.scanline.btm()[i] = Scanline.Pixel.from(.Background, bgr555);
return;
}
@ -826,14 +834,14 @@ pub const Ppu = struct {
const is_top_layer = (top_layer >> layer) & 1 == 1;
if (is_top_layer) {
self.scanline.btm()[i] = Scanline.Pixel.from(bgr555); // this is intentional
self.scanline.btm()[i] = Scanline.Pixel.from(.Background, bgr555); // this is intentional
return;
}
},
}
// If we aren't blending here at all, just add the pixel to the top layer
self.scanline.top()[i] = Scanline.Pixel.from(bgr555);
self.scanline.top()[i] = Scanline.Pixel.from(.Background, bgr555);
}
const WindowBounds = enum { win0, win1, out };
@ -859,7 +867,7 @@ pub const Ppu = struct {
fn shouldDrawBackground(self: *Self, comptime layer: u2, bounds: ?WindowBounds, i: usize) bool {
switch (self.bld.cnt.mode.read()) {
0b00 => if (self.scanline.top()[i] == .set) return false, // pass through
0b00 => if (self.scanline.top()[i].isSet()) return false, // pass through
0b01 => blk: {
// BLD_ALPHA
@ -868,7 +876,7 @@ pub const Ppu = struct {
const is_btm_layer = (btm_layer >> layer) & 1 == 1;
if (is_btm_layer) {
if (self.scanline.btm()[i] == .set) return false;
if (self.scanline.btm()[i].isSet()) return false;
// In some previous iteration we have determined that an opaque pixel was drawn at this position
// therefore there's no reason to draw anything here
@ -892,7 +900,7 @@ pub const Ppu = struct {
break :blk;
}
if (self.scanline.top()[i] == .set) return false;
if (self.scanline.top()[i].isSet()) return false;
},
0b10, 0b11 => {
// BLD_WHITE and BLD_BLACK
@ -900,7 +908,9 @@ pub const Ppu = struct {
// we want to treat the bottom layer the same as the top (despite it being repurposed)
// so we should apply the same logic to the bottom layer
if (self.scanline.top()[i] == .set) return false;
if (self.scanline.top()[i].isSet()) return false;
// If the bottom pixel comes rom a sprite, draw the pixel anyways
if (self.scanline.btm()[i] == .set) return false;
},
}
@ -1409,10 +1419,8 @@ fn alphaBlend(top: u16, btm: u16, bldalpha: io.BldAlpha) u16 {
}
fn shouldDrawSprite(bldcnt: io.BldCnt, scanline: *Scanline, x: u9) bool {
if (scanline.top()[x] == .set) return false;
switch (bldcnt.mode.read()) {
0b00 => if (scanline.top()[x] == .set) return false, // pass through
0b00 => if (scanline.top()[x].isSet()) return false,
0b01 => {
// BLD_ALPHA
@ -1421,13 +1429,13 @@ fn shouldDrawSprite(bldcnt: io.BldCnt, scanline: *Scanline, x: u9) bool {
const btm_layers = bldcnt.layer_b.read();
const is_btm_layer = (btm_layers >> 4) & 1 == 1;
if (is_btm_layer and scanline.btm()[x] == .set) return false;
if (is_btm_layer and scanline.btm()[x].isSet()) return false;
if (scanline.top()[x] == .set) return false;
if (scanline.top()[x].isSet()) return false;
},
0b10, 0b11 => {
if (scanline.top()[x] == .set) return false;
if (scanline.btm()[x] == .set) return false;
if (scanline.top()[x].isSet()) return false;
if (scanline.btm()[x].isSet()) return false;
},
}
@ -1443,7 +1451,7 @@ fn drawSpritePixel(bldcnt: io.BldCnt, scanline: *Scanline, x: u9, bgr555: u16) v
const is_top_layer = (top_layers >> 4) & 1 == 1;
if (is_top_layer) {
scanline.top()[x] = Scanline.Pixel.from(bgr555);
scanline.top()[x] = Scanline.Pixel.from(.Sprite, bgr555);
return;
}
@ -1451,7 +1459,7 @@ fn drawSpritePixel(bldcnt: io.BldCnt, scanline: *Scanline, x: u9, bgr555: u16) v
const is_btm_layer = (btm_layers >> 4) & 1 == 1;
if (is_btm_layer) {
scanline.btm()[x] = Scanline.Pixel.from(bgr555);
scanline.btm()[x] = Scanline.Pixel.from(.Sprite, bgr555);
return;
}
@ -1468,25 +1476,39 @@ fn drawSpritePixel(bldcnt: io.BldCnt, scanline: *Scanline, x: u9, bgr555: u16) v
const is_top_layer = (top_layers >> 4) & 1 == 1;
if (is_top_layer) {
scanline.btm()[x] = Scanline.Pixel.from(bgr555); // This is intentional
scanline.btm()[x] = Scanline.Pixel.from(.Sprite, bgr555); // This is intentional
return;
}
},
}
scanline.top()[x] = Scanline.Pixel.from(bgr555);
scanline.top()[x] = Scanline.Pixel.from(.Sprite, bgr555);
}
const Scanline = struct {
const Self = @This();
const Pixel = union(enum) {
// TODO: Rename
const Layer = enum { Background, Sprite };
set: u16,
obj_set: u16,
unset: void,
hidden: void,
fn from(bgr555: u16) Pixel {
return .{ .set = bgr555 };
fn from(comptime layer: Layer, bgr555: u16) Pixel {
return switch (layer) {
.Background => .{ .set = bgr555 },
.Sprite => .{ .obj_set = bgr555 },
};
}
pub fn isSet(self: @This()) bool {
return switch (self) {
.set, .obj_set => true,
.unset, .hidden => false,
};
}
};