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chore: improve readability of sprite drawing code a bit

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-11-02 10:40:07 -03:00
parent be4396fb0d
commit c73966135c
1 changed files with 21 additions and 37 deletions
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58
src/core/ppu.zig
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@ -263,8 +263,7 @@ pub const Ppu = struct {
scanline: Scanline, scanline: Scanline,
pub fn init(allocator: Allocator, sched: *Scheduler) !Self { pub fn init(allocator: Allocator, sched: *Scheduler) !Self {
// Queue first Hblank sched.push(.Draw, 240 * 4); // Add first PPU Event to Scheduler
sched.push(.Draw, 240 * 4);
const sprites = try allocator.create([128]?Sprite); const sprites = try allocator.create([128]?Sprite);
std.mem.set(?Sprite, sprites, null); std.mem.set(?Sprite, sprites, null);
@ -324,20 +323,16 @@ pub const Ppu = struct {
// Only consider enabled Sprites // Only consider enabled Sprites
if (attr0.is_affine.read() or !attr0.disabled.read()) { if (attr0.is_affine.read() or !attr0.disabled.read()) {
const attr1 = @bitCast(Attr1, self.oam.read(u16, i + 2)); const attr1 = @bitCast(Attr1, self.oam.read(u16, i + 2));
const sprite_height = spriteDimensions(attr0.shape.read(), attr1.size.read())[1];
// When fetching sprites we only care about ones that could be rendered // When fetching sprites we only care about ones that could be rendered
// on this scanline // on this scanline
const iy = @bitCast(i8, y); var y_pos: i32 = attr0.y.read();
if (y_pos >= 160) y_pos -= 256; // fleroviux's solution to negative positions
const start = attr0.y.read();
const istart = @bitCast(i8, start);
const end = start +% spriteDimensions(attr0.shape.read(), attr1.size.read())[1];
const iend = @bitCast(i8, end);
// Sprites are expected to be able to wraparound, we perform the same check // Sprites are expected to be able to wraparound, we perform the same check
// for unsigned and signed values so that we handle all valid sprite positions // for unsigned and signed values so that we handle all valid sprite positions
if ((start <= y and y < end) or (istart <= iy and iy < iend)) { if (y_pos <= y and y < (y_pos + sprite_height)) {
for (self.scanline_sprites) |*maybe_sprite| { for (self.scanline_sprites) |*maybe_sprite| {
if (maybe_sprite.* == null) { if (maybe_sprite.* == null) {
maybe_sprite.* = Sprite.init(attr0, attr1, @bitCast(Attr2, self.oam.read(u16, i + 4))); maybe_sprite.* = Sprite.init(attr0, attr1, @bitCast(Attr2, self.oam.read(u16, i + 4)));
@ -364,8 +359,6 @@ pub const Ppu = struct {
} }
fn drawAffineSprite(self: *Self, sprite: AffineSprite) void { fn drawAffineSprite(self: *Self, sprite: AffineSprite) void {
const iy = @bitCast(i8, self.vcount.scanline.read());
const is_8bpp = sprite.is8bpp(); const is_8bpp = sprite.is8bpp();
const tile_id: u32 = sprite.tileId(); const tile_id: u32 = sprite.tileId();
const obj_mapping = self.dispcnt.obj_mapping.read(); const obj_mapping = self.dispcnt.obj_mapping.read();
@ -374,25 +367,22 @@ pub const Ppu = struct {
const char_base = 0x4000 * 4; const char_base = 0x4000 * 4;
const y = self.vcount.scanline.read();
var i: u9 = 0; var i: u9 = 0;
while (i < sprite.width) : (i += 1) { while (i < sprite.width) : (i += 1) {
const x = (sprite.x() +% i) % width; const x = (sprite.x() +% i) % width;
const ix = @bitCast(i9, x);
if (!shouldDrawSprite(self.bld.cnt, &self.scanline, x)) continue; if (!shouldDrawSprite(self.bld.cnt, &self.scanline, x)) continue;
const sprite_start = sprite.x(); var x_pos: i32 = sprite.x();
const isprite_start = @bitCast(i9, sprite_start); if (x_pos >= 240) x_pos -= 512;
const sprite_end = sprite_start +% sprite.width;
const isprite_end = @bitCast(i9, sprite_end);
const condition = (sprite_start <= x and x < sprite_end) or (isprite_start <= ix and ix < isprite_end); if (!(x_pos <= x and x < (x_pos + sprite.width))) continue;
if (!condition) continue;
// Sprite is within bounds and therefore should be rendered // Sprite is within bounds and therefore should be rendered
// std.math.absInt is branchless // std.math.absInt is branchless
const tile_x = @bitCast(u9, std.math.absInt(ix - @bitCast(i9, sprite.x())) catch unreachable); const tile_x = @bitCast(u32, @as(i32, std.math.absInt(@as(i32, x) - x_pos) catch unreachable));
const tile_y = @bitCast(u8, std.math.absInt(iy -% @bitCast(i8, sprite.y())) catch unreachable); const tile_y = @bitCast(u32, @as(i32, std.math.absInt(@bitCast(i8, y) -% @bitCast(i8, sprite.y())) catch unreachable));
const row = @truncate(u3, tile_y); const row = @truncate(u3, tile_y);
const col = @truncate(u3, tile_x); const col = @truncate(u3, tile_x);
@ -414,8 +404,6 @@ pub const Ppu = struct {
} }
fn drawSprite(self: *Self, sprite: Sprite) void { fn drawSprite(self: *Self, sprite: Sprite) void {
const iy = @bitCast(i8, self.vcount.scanline.read());
const is_8bpp = sprite.is8bpp(); const is_8bpp = sprite.is8bpp();
const tile_id: u32 = sprite.tileId(); const tile_id: u32 = sprite.tileId();
const obj_mapping = self.dispcnt.obj_mapping.read(); const obj_mapping = self.dispcnt.obj_mapping.read();
@ -424,31 +412,27 @@ pub const Ppu = struct {
const char_base = 0x4000 * 4; const char_base = 0x4000 * 4;
const y = self.vcount.scanline.read();
var i: u9 = 0; var i: u9 = 0;
while (i < sprite.width) : (i += 1) { while (i < sprite.width) : (i += 1) {
const x = (sprite.x() +% i) % width; const x = (sprite.x() +% i) % width;
const ix = @bitCast(i9, x);
if (!shouldDrawSprite(self.bld.cnt, &self.scanline, x)) continue; if (!shouldDrawSprite(self.bld.cnt, &self.scanline, x)) continue;
const sprite_start = sprite.x(); var x_pos: i32 = sprite.x();
const isprite_start = @bitCast(i9, sprite_start); if (x_pos >= 240) x_pos -= 512;
const sprite_end = sprite_start +% sprite.width;
const isprite_end = @bitCast(i9, sprite_end);
const condition = (sprite_start <= x and x < sprite_end) or (isprite_start <= ix and ix < isprite_end); if (!(x_pos <= x and x < (x_pos + sprite.width))) continue;
if (!condition) continue;
// Sprite is within bounds and therefore should be rendered // Sprite is within bounds and therefore should be rendered
// std.math.absInt is branchless const x_diff: i32 = std.math.absInt(@as(i32, x) - x_pos) catch unreachable;
const x_diff = @bitCast(u9, std.math.absInt(ix - @bitCast(i9, sprite.x())) catch unreachable); const y_diff: i32 = std.math.absInt(@bitCast(i8, y) -% @bitCast(i8, sprite.y())) catch unreachable;
const y_diff = @bitCast(u8, std.math.absInt(iy -% @bitCast(i8, sprite.y())) catch unreachable);
// Note that we flip the tile_pos not the (tile_pos % 8) like we do for // Note that we flip the tile_pos not the (tile_pos % 8) like we do for
// Background Tiles. By doing this we mirror the entire sprite instead of // Background Tiles. By doing this we mirror the entire sprite instead of
// just a specific tile (see how sprite.width and sprite.height are involved) // just a specific tile (see how sprite.width and sprite.height are involved)
const tile_y = y_diff ^ if (sprite.vFlip()) (sprite.height - 1) else 0; const tile_x = @intCast(u9, x_diff) ^ if (sprite.hFlip()) (sprite.width - 1) else 0;
const tile_x = x_diff ^ if (sprite.hFlip()) (sprite.width - 1) else 0; const tile_y = @intCast(u8, y_diff) ^ if (sprite.vFlip()) (sprite.height - 1) else 0;
const row = @truncate(u3, tile_y); const row = @truncate(u3, tile_y);
const col = @truncate(u3, tile_x); const col = @truncate(u3, tile_x);