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chore: reimplement object rendering 

TODO: implement affine sprites
This commit is contained in:
Rekai Nyangadzayi Musuka 2022-06-04 13:55:31 -03:00
parent 4eb0d469b3
commit 25d13722f7
1 changed files with 49 additions and 60 deletions
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109
src/ppu.zig
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@ -96,7 +96,7 @@ pub const Ppu = struct {
const attr0 = @bitCast(Attr0, self.oam.read(u16, i));
// Only consider enabled Sprites
if (!attr0.disabled.read()) {
if (attr0.is_affine.read() or !attr0.disabled.read()) {
const attr1 = @bitCast(Attr1, self.oam.read(u16, i + 2));
// When fetching sprites we only care about ones that could be rendered
@ -126,79 +126,68 @@ pub const Ppu = struct {
}
}
/// Draw all relevant sprites on a scanline
fn drawSprites(self: *Self, prio: u2) void {
const char_base = 0x4000 * 4;
const y = @bitCast(i8, self.vcount.scanline.read());
fn drawSprites(self: *Self, layer: u2) void {
// Loop over every fetched sprite
sprite_loop: for (self.scanline_sprites) |maybe_sprites| {
if (maybe_sprites) |sprite| {
// Move on to the next sprite If its of a different priority
if (sprite.priority() != prio) continue :sprite_loop;
if (sprite.attr0.is_affine.read()) continue :sprite_loop; // TODO: Affine Sprites
var i: u9 = 0;
px_loop: while (i < sprite.width) : (i += 1) {
const x = (sprite.x() +% i) % 240;
const ix = @bitCast(i9, x);
// If We've already rendered a pixel here don't overwrite it
if (self.scanline_buf[x] != null) continue :px_loop;
const start = sprite.x();
const istart = @bitCast(i9, start);
const end = start +% sprite.width;
const iend = @bitCast(i9, end);
// By comparing with both signed and unsigned values we ensure that sprites
// are displayed in all valid (AFAIK) configuration
if ((start <= x and x < end) or (istart <= ix and ix < iend)) {
self.drawSpritePixel(char_base, sprite, ix, y);
}
}
for (self.scanline_sprites) |maybe_sprite| {
if (maybe_sprite) |sprite| {
// Skip this sprite if it isn't on the current priority
if (sprite.priority() != layer) continue;
if (sprite.attr0.is_affine.read()) self.drawSprite(sprite) else self.drawSprite(sprite);
} else break;
}
}
/// Draw a Pixel of a Sprite Tile
fn drawSpritePixel(self: *Self, char_base: u32, sprite: Sprite, x: i9, y: i8) void {
// FIXME: We branch on this condition quite a lot
fn drawSprite(self: *Self, sprite: Sprite) void {
const iy = @bitCast(i8, self.vcount.scanline.read());
const is_8bpp = sprite.is_8bpp();
// std.math.absInt is branchless
const x_diff = @bitCast(u9, std.math.absInt(x - @bitCast(i9, sprite.x())) catch unreachable);
const y_diff = @bitCast(u8, std.math.absInt(y -% @bitCast(i8, sprite.y())) catch unreachable);
// 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
// just a specific tile (see how sprite.width and sprite.height are involved)
const tile_y = y_diff ^ if (sprite.v_flip()) (sprite.height - 1) else 0;
const tile_x = x_diff ^ if (sprite.h_flip()) (sprite.width - 1) else 0;
// Like in the background Tiles are 8x8 groups of pixels in 8bpp or 4bpp formats
const tile_id = sprite.tile_id();
const tile_id: u32 = sprite.tile_id();
const obj_mapping = self.dispcnt.obj_mapping.read();
const tile_row_offset: u32 = if (is_8bpp) 8 else 4;
const tile_len: u32 = if (is_8bpp) 0x40 else 0x20;
const row = tile_y & 7;
const col = @truncate(u3, tile_x);
const char_base = 0x4000 * 4;
// When calcualting the inital address, the first entry is always 0x20 * tile_id, even if it is 8bpp
const tile_base = char_base + (0x20 * @as(u32, tile_id)) + (tile_row_offset * row) + if (is_8bpp) col else col >> 1;
var i: u9 = 0;
while (i < sprite.width) : (i += 1) {
const x = (sprite.x() +% i) % width;
const ix = @bitCast(i9, x);
// TODO: Finish that 2D Sprites Test ROM
const offset_base = (tile_x >> 3) * tile_len;
const offset_offset = (tile_y >> 3) * tile_len * if (self.dispcnt.obj_mapping.read()) sprite.width >> 3 else if (is_8bpp) @as(u32, 0x10) else 0x20;
if (self.scanline_buf[x] != null) continue;
const tile_offset = offset_base + offset_offset;
const tile = self.vram.buf[tile_base + tile_offset];
const sprite_start = sprite.x();
const isprite_start = @bitCast(i9, sprite_start);
const sprite_end = sprite_start +% sprite.width;
const isprite_end = @bitCast(i9, sprite_end);
const pal_id: u16 = if (!is_8bpp) get4bppTilePalette(sprite.pal_bank(), col, tile) else tile;
const condition = (sprite_start <= x and x < sprite_end) or (isprite_start <= ix and ix < isprite_end);
if (!condition) continue;
// Sprite Palette starts at 0x0500_0200
if (pal_id != 0) self.scanline_buf[@bitCast(u9, x)] = self.palette.read(u16, 0x200 + pal_id * 2);
// Sprite is within bounds and therefore should be rendered
// std.math.absInt is branchless
const x_diff = @bitCast(u9, std.math.absInt(ix - isprite_start) 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
// 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)
const tile_y = y_diff ^ if (sprite.v_flip()) (sprite.height - 1) else 0;
const tile_x = x_diff ^ if (sprite.h_flip()) (sprite.width - 1) else 0;
const row = @truncate(u3, tile_y);
const col = @truncate(u3, tile_x);
// TODO: Finish that 2D Sprites Test ROM
const tile_base = char_base + (tile_id * 0x20) + (row * tile_row_offset) + if (is_8bpp) col else col >> 1;
const mapping_offset = if (obj_mapping) sprite.width >> 3 else if (is_8bpp) @as(u32, 0x10) else 0x20;
const tile_offset = (tile_x >> 3) * tile_len + (tile_y >> 3) * tile_len * mapping_offset;
const tile = self.vram.buf[tile_base + tile_offset];
const pal_id: u16 = if (!is_8bpp) get4bppTilePalette(sprite.pal_bank(), col, tile) else tile;
// Sprite Palette starts at 0x0500_0200
if (pal_id != 0) self.scanline_buf[x] = self.palette.read(u16, 0x200 + pal_id * 2);
}
}
fn drawAffineBackground(self: *Self, comptime n: u3) void {