feat: implement background alpha blending
This commit is contained in:
parent
5e4fb7b952
commit
02534c5c19
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@ -436,19 +436,16 @@ pub const BackgroundOffset = extern union {
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/// Read / Write
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pub const BldCnt = extern union {
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bg0a: Bit(u16, 0),
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bg1a: Bit(u16, 1),
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bg2a: Bit(u16, 2),
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bg3a: Bit(u16, 3),
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obja: Bit(u16, 4),
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bda: Bit(u16, 5),
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/// BLDCNT{0} is BG0 A
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/// BLDCNT{4} is OBJ A
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/// BLDCNT{5} is BD A
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layer_a: Bitfield(u16, 0, 6),
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mode: Bitfield(u16, 6, 2),
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bg0b: Bit(u16, 8),
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bg1b: Bit(u16, 9),
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bg2b: Bit(u16, 10),
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bg3b: Bit(u16, 11),
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objb: Bit(u16, 12),
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bdb: Bit(u16, 13),
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/// BLDCNT{8} is BG0 B
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/// BLDCNT{12} is OBJ B
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/// BLDCNT{13} is BD B
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layer_b: Bitfield(u16, 8, 6),
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raw: u16,
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};
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210
src/ppu.zig
210
src/ppu.zig
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@ -43,7 +43,7 @@ pub const Ppu = struct {
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alloc: Allocator,
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scanline_sprites: [128]?Sprite,
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scanline_buf: [width]?u16,
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scanline: Scanline,
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pub fn init(alloc: Allocator, sched: *Scheduler) !Self {
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// Queue first Hblank
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@ -52,6 +52,9 @@ pub const Ppu = struct {
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const framebufs = try alloc.alloc(u8, (framebuf_pitch * height) * 2);
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std.mem.set(u8, framebufs, 0);
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const scanline_buf = try alloc.alloc(?u16, width * 2);
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std.mem.set(?u16, scanline_buf, null);
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return Self{
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.vram = try Vram.init(alloc),
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.palette = try Palette.init(alloc),
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@ -70,24 +73,25 @@ pub const Ppu = struct {
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.bldalpha = .{ .raw = 0x0000 },
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.bldy = .{ .raw = 0x0000 },
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.scanline_buf = [_]?u16{null} ** width,
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.scanline = Scanline.init(scanline_buf),
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.scanline_sprites = [_]?Sprite{null} ** 128,
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};
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}
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pub fn deinit(self: Self) void {
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self.framebuf.deinit(self.alloc);
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self.scanline.deinit(self.alloc);
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self.vram.deinit();
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self.palette.deinit();
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self.oam.deinit();
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}
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pub fn setBgOffsets(self: *Self, comptime n: u3, word: u32) void {
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pub fn setBgOffsets(self: *Self, comptime n: u2, word: u32) void {
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self.bg[n].hofs.raw = @truncate(u16, word);
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self.bg[n].vofs.raw = @truncate(u16, word >> 16);
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}
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pub fn setAdjCnts(self: *Self, comptime n: u3, word: u32) void {
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pub fn setAdjCnts(self: *Self, comptime n: u2, word: u32) void {
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self.bg[n].cnt.raw = @truncate(u16, word);
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self.bg[n + 1].cnt.raw = @truncate(u16, word >> 16);
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}
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@ -160,7 +164,7 @@ pub const Ppu = struct {
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const x = (sprite.x() +% i) % width;
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const ix = @bitCast(i9, x);
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if (self.scanline_buf[x] != null) continue;
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if (self.scanline.top()[x] != null) continue;
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const sprite_start = sprite.x();
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const isprite_start = @bitCast(i9, sprite_start);
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@ -187,7 +191,7 @@ pub const Ppu = struct {
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const pal_id: u16 = if (!is_8bpp) get4bppTilePalette(sprite.palBank(), col, tile) else tile;
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// Sprite Palette starts at 0x0500_0200
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if (pal_id != 0) self.scanline_buf[x] = self.palette.read(u16, 0x200 + pal_id * 2);
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if (pal_id != 0) self.scanline.top()[x] = self.palette.read(u16, 0x200 + pal_id * 2);
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}
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}
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@ -207,7 +211,15 @@ pub const Ppu = struct {
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const x = (sprite.x() +% i) % width;
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const ix = @bitCast(i9, x);
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if (self.scanline_buf[x] != null) continue;
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if (self.scanline.top()[x] != null) continue;
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if (self.scanline.btm()[x] != null) {
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if (self.bldcnt.mode.read() != 0b01) continue;
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const b_layers = self.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) continue;
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}
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const sprite_start = sprite.x();
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const isprite_start = @bitCast(i9, sprite_start);
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@ -240,11 +252,26 @@ pub const Ppu = struct {
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const pal_id: u16 = if (!is_8bpp) get4bppTilePalette(sprite.palBank(), col, tile) else tile;
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// Sprite Palette starts at 0x0500_0200
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if (pal_id != 0) self.scanline_buf[x] = self.palette.read(u16, 0x200 + pal_id * 2);
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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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if (self.bldcnt.mode.read() == 0b01) {
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// Alpha Blending
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const a_layers = self.bldcnt.layer_a.read();
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const is_blend_enabled = (a_layers >> 4) & 1 == 1;
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if (is_blend_enabled) {
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self.scanline.btm()[x] = bgr555;
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return;
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}
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}
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self.scanline.top()[x] = bgr555;
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}
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}
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}
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fn drawAffineBackground(self: *Self, comptime n: u3) void {
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fn drawAffineBackground(self: *Self, comptime n: u2) void {
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comptime std.debug.assert(n == 2 or n == 3); // Only BG2 and BG3 can be affine
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const char_base = @as(u32, 0x4000) * self.bg[n].cnt.char_base.read();
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@ -266,7 +293,7 @@ pub const Ppu = struct {
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aff_x += self.aff_bg[n - 2].pa;
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aff_y += self.aff_bg[n - 2].pc;
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if (self.scanline_buf[@as(usize, i)] != null) continue;
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if (!shouldDrawBackground(n, self.bldcnt, &self.scanline, i)) continue;
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if (self.bg[n].cnt.display_overflow.read()) {
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ix = if (ix > px_width) @rem(ix, px_width) else if (ix < 0) px_width + @rem(ix, px_width) else ix;
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@ -283,7 +310,10 @@ 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) self.scanline_buf[i] = self.palette.read(u16, pal_id * 2);
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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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drawToScanlineBuffer(n, self.bldcnt, &self.scanline, i, bgr555);
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}
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}
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// Update BGxX and BGxY
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@ -291,7 +321,7 @@ pub const Ppu = struct {
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self.aff_bg[n - 2].y_latch.? += self.aff_bg[n - 2].pd; // PD is added to BGxY
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}
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fn drawBackround(self: *Self, comptime n: u3) void {
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fn drawBackround(self: *Self, comptime n: u2) void {
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// A Tile in a charblock is a byte, while a Screen Entry is a halfword
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const char_base = 0x4000 * @as(u32, self.bg[n].cnt.char_base.read());
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@ -311,8 +341,7 @@ pub const Ppu = struct {
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var i: u32 = 0;
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while (i < width) : (i += 1) {
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// Exit early if a pixel is already here
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if (self.scanline_buf[i] != null) continue;
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if (!shouldDrawBackground(n, self.bldcnt, &self.scanline, i)) continue;
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const x = hofs + i;
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@ -338,7 +367,10 @@ 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) self.scanline_buf[i] = self.palette.read(u16, pal_id * 2);
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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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drawToScanlineBuffer(n, self.bldcnt, &self.scanline, i, bgr555);
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}
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}
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}
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@ -370,15 +402,19 @@ pub const Ppu = struct {
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}
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// Copy Drawn Scanline to Frame Buffer
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// If there are any nulls present in self.scanline_buf it means that no background drew a pixel there, so draw backdrop
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for (self.scanline_buf) |maybe_px, i| {
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const bgr555 = if (maybe_px) |px| px else self.palette.getBackdrop();
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// If there are any nulls present in self.scanline it means that no background drew a pixel there, so draw backdrop
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for (self.scanline.top()) |maybe_px, i| {
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const maybe_top = maybe_px;
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const maybe_btm = self.scanline.btm()[i];
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// TODO: Why must I reverse this?
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const bgr555 = getBgr555(&self.palette, self.bldalpha, maybe_btm, maybe_top);
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std.mem.writeIntNative(u32, self.framebuf.get(.Emulator)[fb_base + i * @sizeOf(u32) ..][0..@sizeOf(u32)], COLOUR_LUT[bgr555 & 0x7FFF]);
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}
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// Reset Current Scanline Pixel Buffer and list of fetched sprites
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// in prep for next scanline
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std.mem.set(?u16, &self.scanline_buf, null);
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self.scanline.reset();
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std.mem.set(?Sprite, &self.scanline_sprites, null);
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},
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0x1 => {
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@ -394,15 +430,19 @@ pub const Ppu = struct {
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}
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// Copy Drawn Scanline to Frame Buffer
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// If there are any nulls present in self.scanline_buf it means that no background drew a pixel there, so draw backdrop
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for (self.scanline_buf) |maybe_px, i| {
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const bgr555 = if (maybe_px) |px| px else self.palette.getBackdrop();
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// If there are any nulls present in self.scanline.top() it means that no background drew a pixel there, so draw backdrop
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for (self.scanline.top()) |maybe_px, i| {
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const maybe_top = maybe_px;
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const maybe_btm = self.scanline.btm()[i];
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// TODO: Why must I reverse this?
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const bgr555 = getBgr555(&self.palette, self.bldalpha, maybe_btm, maybe_top);
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std.mem.writeIntNative(u32, self.framebuf.get(.Emulator)[fb_base + i * @sizeOf(u32) ..][0..@sizeOf(u32)], COLOUR_LUT[bgr555 & 0x7FFF]);
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}
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// Reset Current Scanline Pixel Buffer and list of fetched sprites
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// in prep for next scanline
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std.mem.set(?u16, &self.scanline_buf, null);
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self.scanline.reset();
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std.mem.set(?Sprite, &self.scanline_sprites, null);
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},
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0x2 => {
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@ -417,15 +457,19 @@ pub const Ppu = struct {
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}
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// Copy Drawn Scanline to Frame Buffer
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// If there are any nulls present in self.scanline_buf it means that no background drew a pixel there, so draw backdrop
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for (self.scanline_buf) |maybe_px, i| {
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const bgr555 = if (maybe_px) |px| px else self.palette.getBackdrop();
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// If there are any nulls present in self.scanline.top() it means that no background drew a pixel there, so draw backdrop
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for (self.scanline.top()) |maybe_px, i| {
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const maybe_top = maybe_px;
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const maybe_btm = self.scanline.btm()[i];
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// TODO: Why must I reverse this?
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const bgr555 = getBgr555(&self.palette, self.bldalpha, maybe_btm, maybe_top);
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std.mem.writeIntNative(u32, self.framebuf.get(.Emulator)[fb_base + i * @sizeOf(u32) ..][0..@sizeOf(u32)], COLOUR_LUT[bgr555 & 0x7FFF]);
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}
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// Reset Current Scanline Pixel Buffer and list of fetched sprites
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// in prep for next scanline
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std.mem.set(?u16, &self.scanline_buf, null);
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self.scanline.reset();
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std.mem.set(?Sprite, &self.scanline_sprites, null);
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},
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0x3 => {
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@ -1006,6 +1050,118 @@ fn toRgba8888Talarubi(bgr555: u16) u32 {
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return @floatToInt(u32, out_r) << 24 | @floatToInt(u32, out_g) << 16 | @floatToInt(u32, out_b) << 8 | 0xFF;
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}
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fn getBgr555(palette: *const Palette, bldalpha: io.BldAlpha, maybe_top: ?u16, maybe_btm: ?u16) u16 {
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if (maybe_top) |top| {
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if (maybe_btm) |btm| return alphaBlend(top, btm, bldalpha);
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return top;
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}
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if (maybe_btm) |btm| return btm;
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return palette.getBackdrop();
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}
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fn alphaBlend(top: u16, btm: u16, bldalpha: io.BldAlpha) u16 {
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const eva: u16 = bldalpha.eva.read();
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const evb: u16 = bldalpha.evb.read();
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const top_r = top & 0x1F;
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const top_g = (top >> 5) & 0x1F;
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const top_b = (top >> 10) & 0x1F;
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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 bld_r = std.math.min(31, (top_r * eva + btm_r * evb) >> 4);
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const bld_g = std.math.min(31, (top_g * eva + btm_g * evb) >> 4);
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const bld_b = std.math.min(31, (top_b * eva + btm_b * evb) >> 4);
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return (bld_b << 10) | (bld_g << 5) | bld_r;
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}
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fn shouldDrawBackground(comptime n: u2, bldcnt: io.BldCnt, scanline: *Scanline, i: usize) bool {
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// If a pixel has been drawn on the top layer, it's because
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// Either the pixel is to be blended with a pixel on the bottom layer
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// or the pixel is not to be blended at all
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// Consequentially, if we find a pixel on the top layer, there's no need
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// to render anything I think?
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if (scanline.top()[i] != null) return false;
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if (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
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// 2. From a Backround that is marked for Blending (Pixel A)
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//
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// We now have to confirm whether this current Background can be used
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// as Pixel B or not.
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// If Alpha Blending isn't enabled, we've aready found a higher
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// priority pixel to render. Move on
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if (bldcnt.mode.read() != 0b01) return false;
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const b_layers = bldcnt.layer_b.read();
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const is_blend_enabled = (b_layers >> n) & 1 == 1;
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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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if (!is_blend_enabled) return false;
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}
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return true;
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}
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fn drawToScanlineBuffer(comptime n: u2, bldcnt: io.BldCnt, scanline: *Scanline, i: usize, bgr555: u16) void {
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if (bldcnt.mode.read() == 0b01) {
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// Standard Alpha Blending
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const a_layers = bldcnt.layer_a.read();
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const is_blend_enabled = (a_layers >> n) & 1 == 1;
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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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if (is_blend_enabled) {
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scanline.btm()[i] = bgr555;
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return;
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}
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}
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scanline.top()[i] = bgr555;
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}
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const Scanline = struct {
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const Self = @This();
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buf: [2][]?u16,
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original: []?u16,
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fn init(buf: []?u16) Self {
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std.debug.assert(buf.len == width * 2);
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const top_slice = buf[0..][0..width];
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const btm_slice = buf[width..][0..width];
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return .{
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.buf = [_][]?u16{ top_slice, btm_slice },
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.original = buf,
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};
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}
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fn reset(self: *Self) void {
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std.mem.set(?u16, self.original, null);
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}
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fn deinit(self: Self, alloc: Allocator) void {
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alloc.free(self.original);
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}
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fn top(self: *Self) []?u16 {
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return self.buf[0];
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}
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fn btm(self: *Self) []?u16 {
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return self.buf[1];
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}
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};
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// Double Buffering Implementation
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const FrameBuffer = struct {
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const Self = @This();
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