fix: resolve issues with sprite mirroring

src/ppu.zig

@@ -8,6 +8,7 @@ const Bit = @import("bitfield").Bit;
 const Bitfield = @import("bitfield").Bitfield;
 
 const Allocator = std.mem.Allocator;
+const log = std.log.scoped(.PPU);
 
 pub const width = 240;
 pub const height = 160;
@@ -76,12 +77,12 @@ pub const Ppu = struct {
         self.bg[n + 1].cnt.raw = @truncate(u16, word >> 16);
     }
 
-    // Search OAM for Sprites that might be rendered on this scanline
+    /// Search OAM for Sprites that might be rendered on this scanline
     fn fetchSprites(self: *Self) void {
         const y = self.vcount.scanline.read();
 
         var i: usize = 0;
-        outer: while (i < self.oam.buf.len) : (i += 8) {
+        search: while (i < self.oam.buf.len) : (i += 8) {
             // Attributes in OAM are 6 bytes long, with 2 bytes of padding
             // Grab Attributes from OAM
             const attr0 = @bitCast(Attr0, self.oam.get16(i));
@@ -101,9 +102,12 @@ pub const Ppu = struct {
                 for (self.scanline_sprites) |*maybe_sprite| {
                     if (maybe_sprite.* == null) {
                         maybe_sprite.* = sprite;
-                        continue :outer;
+                        continue :search;
                     }
                 }
+
+                log.err("Found more than 128 sprites in OAM Search", .{});
+                unreachable;
             }
         }
     }
@@ -138,57 +142,31 @@ pub const Ppu = struct {
                 } else break;
             }
 
-            // // TODO: Scanning OAM for every single pixel is insanely expensive
-            // // This should be done once per scanline (and then check for X bounds every pixel)
-            // var j: u32 = 0;
-            // while (j < self.oam.buf.len) : (j += 8) {
-            //     // Attributes in OAM are 6 bytes long, with 2 bytes of padding
-            //     // Grab Attributes from OAM
-            //     const attr0 = @bitCast(Attr0, self.oam.get16(j));
-            //     const attr1 = @bitCast(Attr1, self.oam.get16(j + 2));
-            //     const attr2 = @bitCast(Attr2, self.oam.get16(j + 4));
-
-            //     // Only consider enabled sprites on the current priority
-            //     if (attr0.disabled.read() or attr2.rel_prio.read() != prio) continue;
-
-            //     // Determine sprite bounds
-            //     const d = spriteDimensions(attr0.shape.read(), attr1.size.read());
-            //     const sy = attr0.y.read();
-            //     const sx = attr1.x.read();
-            //     const sx_end = sx + d[0];
-            //     const sy_end = sy + d[1];
-
-            //     // If sprite is in range
-            //     if (sy < y and sy_end > y and sx < x and sx_end > x) {
-            //         maybe_sprite = Sprite.init(attr0, attr1, attr2);
-            //         break;
-            //     }
-            // }
-
             // If we didn't find a sprite, progress to the next pixel
             const sprite: Sprite = if (maybe_sprite) |s| s else continue;
             const is_8bpp = sprite.is_8bpp();
 
             // Y and X coordinates within the context of a singular 8x8 tile
-            const tile_y = y - sprite.y();
-            const tile_x = x - sprite.x();
+            const tile_y: u16 = (y - sprite.y()) ^ if (sprite.v_flip()) (sprite.height - 1) else 0;
+            const tile_x = (x - sprite.x()) ^ if (sprite.h_flip()) (sprite.width - 1) else 0;
 
             const tile_id: u32 = sprite.tile_id();
             const tile_row_offset: u32 = if (is_8bpp) 8 else 4;
             const tile_len: u32 = if (is_8bpp) 0x40 else 0x20;
 
-            const row = if (sprite.v_flip()) 7 - (tile_y % 8) else tile_y % 8;
-            const col = if (sprite.h_flip()) 7 - (tile_x % 8) else tile_x % 8;
+            const row = tile_y % 8;
+            const col = tile_x % 8;
 
             const tile_base: u32 = char_base + (0x20 * tile_id) + (tile_row_offset * row) + if (is_8bpp) col else col / 2;
 
-            var tile_offset = (tile_x >> 3) * tile_len;
+            var tile_offset = (tile_x / 8) * tile_len;
             if (self.dispcnt.obj_mapping.read()) {
                 // One Dimensional
-                tile_offset += (tile_y / 8) * tile_len * (sprite.width >> 3);
+                tile_offset += (tile_y / 8) * tile_len * (sprite.width / 8);
             } else {
                 // Two Dimensional
-                tile_offset += (@as(u32, tile_y) >> 3) * tile_len * 0x20;
+                // TODO: This doesn't work
+                tile_offset += (tile_y / 8) * tile_len * 0x20;
             }
 
             const tile = self.vram.buf[tile_base + tile_offset];
@@ -561,7 +539,7 @@ const Sprite = struct {
         return self.attr2.tile_id.read();
     }
 
-    fn pal_bank(self: *const Self) u3 {
+    fn pal_bank(self: *const Self) u4 {
         return self.attr2.pal_bank.read();
     }
 
@@ -604,7 +582,7 @@ const Attr1 = extern union {
 const Attr2 = extern union {
     tile_id: Bitfield(u16, 0, 10),
     rel_prio: Bitfield(u16, 10, 2),
-    pal_bank: Bitfield(u16, 12, 3),
+    pal_bank: Bitfield(u16, 12, 4),
 };
 
 fn spriteDimensions(shape: u2, size: u2) [2]u16 {