chore: reimplement alpha blending
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parent
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acdb270793
344
src/core/ppu.zig
344
src/core/ppu.zig
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@ -398,7 +398,7 @@ pub const Ppu = struct {
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// Sprite Palette starts at 0x0500_0200
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if (pal_id != 0) {
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const bgr555 = self.palette.read(u16, 0x200 + pal_id * 2);
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copyToSpriteBuffer(self.bld.cnt, &self.scanline, x, bgr555);
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drawSpritePixel(self.bld.cnt, &self.scanline, x, bgr555);
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}
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}
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}
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@ -448,7 +448,7 @@ pub const Ppu = struct {
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// Sprite Palette starts at 0x0500_0200
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if (pal_id != 0) {
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const bgr555 = self.palette.read(u16, 0x200 + pal_id * 2);
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copyToSpriteBuffer(self.bld.cnt, &self.scanline, x, bgr555);
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drawSpritePixel(self.bld.cnt, &self.scanline, x, bgr555);
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}
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}
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}
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@ -493,10 +493,7 @@ pub const Ppu = struct {
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const tile_addr = char_base + (tile_id * 0x40) + (row * 0x8) + col;
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const pal_id: u16 = self.vram.buf[tile_addr];
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if (pal_id != 0) {
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const bgr555 = self.palette.read(u16, pal_id * 2);
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self.copyToBackgroundBuffer(n, win_bounds, i, bgr555);
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}
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if (pal_id != 0) self.drawBackgroundPixel(n, i, self.palette.read(u16, pal_id * 2));
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}
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// Update BGxX and BGxY
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@ -551,10 +548,7 @@ pub const Ppu = struct {
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// and then we can index the palette
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const pal_id: u16 = if (!is_8bpp) get4bppTilePalette(entry.pal_bank.read(), col, tile) else tile;
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if (pal_id != 0) {
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const bgr555 = self.palette.read(u16, pal_id * 2);
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self.copyToBackgroundBuffer(n, win_bounds, i, bgr555);
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}
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if (pal_id != 0) self.drawBackgroundPixel(n, i, self.palette.read(u16, pal_id * 2));
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}
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}
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@ -669,8 +663,7 @@ pub const Ppu = struct {
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// FIXME: @ptrCast between slices changing the length isn't implemented yet
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const framebuf = @ptrCast([*]u32, @alignCast(@alignOf(u32), self.framebuf.get(.Emulator)));
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for (self.scanline.top()) |maybe_px, i| {
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const maybe_top = maybe_px;
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for (self.scanline.top()) |maybe_top, i| {
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const maybe_btm = self.scanline.btm()[i];
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const bgr555 = self.getBgr555(maybe_top, maybe_btm);
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@ -683,12 +676,25 @@ pub const Ppu = struct {
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std.mem.set(?Sprite, self.scanline_sprites, null);
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}
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fn getBgr555(self: *Self, maybe_top: ?u16, maybe_btm: ?u16) u16 {
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if (maybe_btm) |btm| {
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return switch (self.bld.cnt.mode.read()) {
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0b00 => if (maybe_top) |top| top else btm,
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0b01 => if (maybe_top) |top| alphaBlend(btm, top, self.bld.alpha) else btm,
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0b10 => blk: {
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fn getBgr555(self: *Self, maybe_top: Scanline.Pixel, maybe_btm: Scanline.Pixel) u16 {
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return switch (self.bld.cnt.mode.read()) {
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0b00 => switch (maybe_top) {
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.set => |top| top,
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else => self.palette.backdrop(),
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},
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0b01 => switch (maybe_top) {
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.set => |top| switch (maybe_btm) {
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.set => |btm| alphaBlend(top, btm, self.bld.alpha), // ALPHA_BLEND
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else => top,
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},
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else => switch (maybe_btm) {
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.set => |btm| btm,
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else => self.palette.backdrop(),
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},
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},
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0b10 => switch (maybe_btm) {
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.set => |btm| blk: {
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// BLD_WHITE
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const evy: u16 = self.bld.y.evy.read();
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const r = btm & 0x1F;
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@ -701,51 +707,87 @@ pub const Ppu = struct {
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break :blk (bld_b << 10) | (bld_g << 5) | bld_r;
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},
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0b11 => blk: {
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else => switch (maybe_top) {
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.set => |top| top,
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else => self.palette.backdrop(),
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},
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},
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0b11 => switch (maybe_btm) {
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.set => |btm| blk: {
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// BLD_BLACK
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const evy: u16 = self.bld.y.evy.read();
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const btm_r = btm & 0x1F;
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const btm_g = (btm >> 5) & 0x1F;
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const btm_b = (btm >> 10) & 0x1F;
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const r = btm & 0x1F;
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const g = (btm >> 5) & 0x1F;
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const b = (btm >> 10) & 0x1F;
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const bld_r = btm_r - ((btm_r * evy) >> 4);
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const bld_g = btm_g - ((btm_g * evy) >> 4);
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const bld_b = btm_b - ((btm_b * evy) >> 4);
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const bld_r = r - ((r * evy) >> 4);
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const bld_g = g - ((g * evy) >> 4);
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const bld_b = b - ((b * evy) >> 4);
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break :blk (bld_b << 10) | (bld_g << 5) | bld_r;
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},
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};
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}
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if (maybe_top) |top| return top;
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return self.palette.backdrop();
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else => switch (maybe_top) {
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.set => |top| top,
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else => self.palette.backdrop(),
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},
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},
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};
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}
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fn copyToBackgroundBuffer(self: *Self, comptime n: u2, bounds: ?WindowBounds, i: usize, bgr555: u16) void {
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if (self.bld.cnt.mode.read() != 0b00) {
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// Standard Alpha Blending
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const a_layers = self.bld.cnt.layer_a.read();
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const is_blend_enabled = (a_layers >> n) & 1 == 1;
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fn drawBackgroundPixel(self: *Self, comptime layer: u2, i: usize, bgr555: u16) void {
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// When writing to the scanline buffer, we want to be aware of a top and bottom layer. Some preconditions were
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// already determined by shouldDrawBackground, so we should be aware of what we can assume to be true or false
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// If Alpha Blending is enabled and we've found an eligible layer for
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// Pixel A, store the pixel in the bottom pixel buffer
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switch (self.bld.cnt.mode.read()) {
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0b00 => {}, // pass through
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0b01 => {
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// We are to alpha blend here so we should pay attention to which layer ths pixel should be written to
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// FIXME: We redo work here that we've already figured out. Is this worth refactorning?
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const win_part = if (bounds) |win| blk: {
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// Window Enabled
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break :blk switch (win) {
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.win0 => self.win.in.w0_bld.read(),
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.win1 => self.win.in.w1_bld.read(),
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.out => self.win.out.out_bld.read(),
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};
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} else true;
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// If the current layer is makred as Layer A, write to top buffer
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const top_layer = self.bld.cnt.layer_a.read();
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const is_top_layer = (top_layer >> layer) & 1 == 1;
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if (win_part and is_blend_enabled) {
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self.scanline.btm()[i] = bgr555;
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return;
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}
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if (is_top_layer) {
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self.scanline.top()[i] = Scanline.Pixel.from(bgr555);
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return;
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}
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// If the current layer is marked as Layer B, we want to continue if there's an available space on that buffer
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const btm_layer = self.bld.cnt.layer_b.read();
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const is_btm_layer = (btm_layer >> layer) & 1 == 1;
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if (is_btm_layer) {
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self.scanline.btm()[i] = Scanline.Pixel.from(bgr555);
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return;
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}
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// The code we're about to fall-through to assumes that alpha blending takes place. In order to withold all invariants
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// we need to discard anything that might be in the bottom buffer.
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self.scanline.btm()[i] = .hidden;
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},
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0b10, 0b11 => {
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// BLD_WHITE, BLD_BLACK
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// Weare to blend with White or black here. By convention we store regular ol' pixels in the top layer, which means that if we want to
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// treat some pixels (in this case the ones relegated to blending) we need to keep them separate as we can't apply the blending to the top layer.
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// While in these modes, (and since this is a scanline renderer), the bottom layer will be completely unused. While it's a bit unintuitive, since we'll
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// be moving layer A pixels there, we will repurpose the bottom layer as the "to blend", layer
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// If the current layer is makred as Layer A, write to top buffer
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const top_layer = self.bld.cnt.layer_a.read();
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const is_top_layer = (top_layer >> layer) & 1 == 1;
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if (is_top_layer) {
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self.scanline.btm()[i] = Scanline.Pixel.from(bgr555); // this is intentional
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return;
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}
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},
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}
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self.scanline.top()[i] = bgr555;
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// If we aren't blending here at all, just add the pixel to the top layer
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self.scanline.top()[i] = Scanline.Pixel.from(bgr555);
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}
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const WindowBounds = enum { win0, win1, out };
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@ -763,48 +805,76 @@ pub const Ppu = struct {
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return .out;
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}
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fn shouldDrawBackground(self: *Self, comptime n: u2, bounds: ?WindowBounds, i: usize) bool {
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// If a pixel has been drawn on the top layer, it's because:
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// 1. The pixel is to be blended with a pixel on the bottom layer
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// 2. The pixel is not to be blended at all
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// Also, if we find a pixel on the top layer we don't need to bother with this I think?
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if (self.scanline.top()[i] != null) return false;
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fn shouldDrawBackground(self: *Self, comptime layer: u2, bounds: ?WindowBounds, i: usize) bool {
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switch (self.bld.cnt.mode.read()) {
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0b00 => if (self.scanline.top()[i] == .set) return false, // pass through
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0b01 => blk: {
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// BLD_ALPHA
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if (bounds) |win| {
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switch (win) {
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.win0 => if ((self.win.in.w0_bg.read() >> n) & 1 == 0) return false,
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.win1 => if ((self.win.in.w1_bg.read() >> n) & 1 == 0) return false,
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.out => if ((self.win.out.out_bg.read() >> n) & 1 == 0) return false,
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// If the current layer is marked as Layer B, we want to continue if there's an available space on that buffer
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const btm_layer = self.bld.cnt.layer_b.read();
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const is_btm_layer = (btm_layer >> layer) & 1 == 1;
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if (is_btm_layer) {
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if (self.scanline.btm()[i] == .set) return false;
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// In some previous iteration we have determined that an opaque pixel was drawn at this position
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// therefore there's no reason to draw anything here
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if (self.scanline.btm()[i] == .hidden) return false;
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// We have a pixel and we know it to be a part of hte bottom layer.
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// when getBgr555 sees that thre's a pixel in the top and bottom layer it chooses to blend the two
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// Meaning that if we want to prevent Alpha Blending from happening (like for example if a window is preventing it)
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// we need to make that happen now.
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// We can do this by not drawing the bottom pixel, since with alpha blending disabled it wouldn't be visible anyways
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// if (bounds) |win| {
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// switch (win) {
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// .win0 => if (!self.win.in.w0_bld.read()) return false,
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// .win1 => if (!self.win.in.w1_bld.read()) return false,
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// .out => if (!self.win.out.out_bld.read()) return false,
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// }
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// }
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break :blk;
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}
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if (self.scanline.top()[i] == .set) return false;
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},
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0b10, 0b11 => {
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// BLD_WHITE and BLD_BLACK
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// we want to treat the bottom layer the same as the top (despite it being repurposed)
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// so we should apply the same logic to the bottom layer
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if (self.scanline.top()[i] == .set) return false;
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if (self.scanline.btm()[i] == .set) return false;
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},
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}
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// At this point we will have exited early if we determined that we'd be overwriting a pixel
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// with a higher priority. We can now move own to determining whether the pixel is visible or not
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// The first thing that may or may not affect visibility is windowing. We should check to see if ths pixel is in bounds
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// of of the background Window if it is enabled
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// TODO: Do Window Bounds checking here instead of outside this function?
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if (bounds) |window| {
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// If this parameter is non-null, we know that:
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// 1. Win0, Win1 or WinObj are enabled
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// 2. This specific pixel exists within the range of a window
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// Here, we check to see if the Window for this background is enabled. If not, we won't render the pixel
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// FIXME: We perform needless computations on Window Bounds by checking for enable here after we've already computed this information
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switch (window) {
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.win0 => if ((self.win.in.w0_bg.read() >> layer) & 1 == 0) return false,
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.win1 => if ((self.win.in.w1_bg.read() >> layer) & 1 == 0) return false,
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.out => if ((self.win.out.out_bg.read() >> layer) & 1 == 0) return false,
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}
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}
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if (self.scanline.btm()[i] != null) {
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// The pixel found in the bottom layer is:
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// 1. From a higher priority background
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// 2. From a background that is marked for blending (Pixel A)
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// If Alpha Blending isn't enabled, then we've already found a higher prio
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// pixel, we can return early
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if (self.bld.cnt.mode.read() != 0b01) return false;
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const b_layers = self.bld.cnt.layer_b.read();
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const win_part = if (bounds) |win| blk: {
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// Window Enabled
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break :blk switch (win) {
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.win0 => self.win.in.w0_bld.read(),
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.win1 => self.win.in.w1_bld.read(),
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.out => self.win.out.out_bld.read(),
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};
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} else true;
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// If the Background is not marked for blending, we've already found
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// a higher priority pixel, move on.
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const is_blend_enabled = win_part and ((b_layers >> n) & 1 == 1);
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if (!is_blend_enabled) return false;
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}
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// Otherwise, return true
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return true;
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}
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@ -1287,56 +1357,106 @@ fn alphaBlend(top: u16, btm: u16, bldalpha: io.BldAlpha) u16 {
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}
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fn shouldDrawSprite(bldcnt: io.BldCnt, scanline: *Scanline, x: u9) bool {
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if (scanline.top()[x] != null) return false;
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if (scanline.top()[x] == .set) return false;
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if (scanline.btm()[x] != null) {
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if (bldcnt.mode.read() != 0b01) return false;
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switch (bldcnt.mode.read()) {
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0b00 => if (scanline.top()[x] == .set) return false, // pass through
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0b01 => {
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// BLD_ALPHA
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const b_layers = bldcnt.layer_b.read();
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const is_blend_enabled = (b_layers >> 4) & 1 == 1;
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if (!is_blend_enabled) return false;
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// We want to check if we're concerned aout the bottom layer first
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// because if so, the top layer already having a pixel is OK
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const btm_layers = bldcnt.layer_b.read();
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const is_btm_layer = (btm_layers >> 4) & 1 == 1;
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if (is_btm_layer and scanline.btm()[x] == .set) return false;
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if (scanline.top()[x] == .set) return false;
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},
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0b10, 0b11 => {
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if (scanline.top()[x] == .set) return false;
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if (scanline.btm()[x] == .set) return false;
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},
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}
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return true;
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}
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fn copyToSpriteBuffer(bldcnt: io.BldCnt, scanline: *Scanline, x: u9, bgr555: u16) void {
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if (bldcnt.mode.read() != 0b00) {
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// Alpha Blending
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const a_layers = bldcnt.layer_a.read();
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const is_blend_enabled = (a_layers >> 4) & 1 == 1;
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fn drawSpritePixel(bldcnt: io.BldCnt, scanline: *Scanline, x: u9, bgr555: u16) void {
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switch (bldcnt.mode.read()) {
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0b00 => {}, // pass through
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0b01 => {
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// BLD_ALPHA
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const top_layers = bldcnt.layer_a.read();
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const is_top_layer = (top_layers >> 4) & 1 == 1;
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if (is_blend_enabled) {
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scanline.btm()[x] = bgr555;
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return;
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}
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if (is_top_layer) {
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scanline.top()[x] = Scanline.Pixel.from(bgr555);
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return;
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}
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const btm_layers = bldcnt.layer_b.read();
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const is_btm_layer = (btm_layers >> 4) & 1 == 1;
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if (is_btm_layer) {
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scanline.btm()[x] = Scanline.Pixel.from(bgr555);
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return;
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}
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// We're rendering a normal pixel that isn't alpha blended
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// we can mark the pixel on the bottom layer as hidden
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scanline.btm()[x] = .hidden;
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},
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0b10, 0b11 => {
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// This is explained in drawBackgroundPixel, we're reusing the bottom layer to draw layer A pixels we will want to
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// later blend with WHITE or BLACK
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const top_layers = bldcnt.layer_a.read();
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const is_top_layer = (top_layers >> 4) & 1 == 1;
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if (is_top_layer) {
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scanline.btm()[x] = Scanline.Pixel.from(bgr555); // This is intentional
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return;
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}
|
||||
},
|
||||
}
|
||||
|
||||
scanline.top()[x] = bgr555;
|
||||
scanline.top()[x] = Scanline.Pixel.from(bgr555);
|
||||
}
|
||||
|
||||
const Scanline = struct {
|
||||
const Self = @This();
|
||||
|
||||
layers: [2][]?u16,
|
||||
buf: []?u16,
|
||||
const Pixel = union(enum) {
|
||||
set: u16,
|
||||
unset: void,
|
||||
hidden: void,
|
||||
|
||||
fn from(bgr555: u16) Pixel {
|
||||
return .{ .set = bgr555 };
|
||||
}
|
||||
};
|
||||
|
||||
layers: [2][]Pixel,
|
||||
buf: []Pixel,
|
||||
|
||||
allocator: Allocator,
|
||||
|
||||
fn init(allocator: Allocator) !Self {
|
||||
const buf = try allocator.alloc(?u16, width * 2); // Top & Bottom Scanline
|
||||
std.mem.set(?u16, buf, null);
|
||||
const buf = try allocator.alloc(Pixel, width * 2); // Top & Bottom Scanline
|
||||
std.mem.set(Pixel, buf, .unset);
|
||||
|
||||
return .{
|
||||
// Top & Bototm Layers
|
||||
.layers = [_][]?u16{ buf[0..][0..width], buf[width..][0..width] },
|
||||
.layers = [_][]Pixel{ buf[0..][0..width], buf[width..][0..width] },
|
||||
.buf = buf,
|
||||
.allocator = allocator,
|
||||
};
|
||||
}
|
||||
|
||||
fn reset(self: *Self) void {
|
||||
std.mem.set(?u16, self.buf, null);
|
||||
std.mem.set(Pixel, self.buf, .unset);
|
||||
}
|
||||
|
||||
fn deinit(self: *Self) void {
|
||||
|
|
@ -1344,11 +1464,11 @@ const Scanline = struct {
|
|||
self.* = undefined;
|
||||
}
|
||||
|
||||
fn top(self: *Self) []?u16 {
|
||||
fn top(self: *Self) []Pixel {
|
||||
return self.layers[0];
|
||||
}
|
||||
|
||||
fn btm(self: *Self) []?u16 {
|
||||
fn btm(self: *Self) []Pixel {
|
||||
return self.layers[1];
|
||||
}
|
||||
};
|
||||
|
|
|
|||
Loading…
Reference in New Issue