chore: crude background window impl (no affine)

src/ppu.zig

@@ -306,7 +306,7 @@ pub const Ppu = struct {
         self.aff_bg[n - 2].y_latch.? += self.aff_bg[n - 2].pd; // PD is added to BGxY
     }
 
-    fn drawBackround(self: *Self, comptime n: u2) void {
+    fn drawBackground(self: *Self, comptime n: u2) void {
         // A Tile in a charblock is a byte, while a Screen Entry is a halfword
 
         const char_base = 0x4000 * @as(u32, self.bg[n].cnt.char_base.read());
@@ -330,6 +330,59 @@ pub const Ppu = struct {
 
             const x = hofs + i;
 
+            const win0 = self.dispcnt.win_enable.read() & 1 == 1;
+            const win1 = (self.dispcnt.win_enable.read() >> 1) & 1 == 1;
+            const winObj = self.dispcnt.obj_win_enable.read();
+
+            if (win0 or win1 or winObj) blk: {
+                // Window is enabled
+                const win0_in = (self.win.in.w0_bg.read() >> n) & 1 == 1;
+                const win1_in = (self.win.in.w1_bg.read() >> n) & 1 == 1;
+                const win_out = (self.win.out.out_bg.read() >> n) & 1 == 1;
+
+                if (win0) {
+                    const h = self.win.h[0];
+                    const v = self.win.v[0];
+
+                    const y1 = v.y1.read();
+                    const y2 = if (y1 > v.y2.read()) 160 else std.math.min(160, v.y2.read());
+
+                    if (y1 <= y and y < y2) {
+                        // Within Y bounds
+                        const x1 = h.x1.read();
+                        const x2 = if (x1 > h.x2.read()) 240 else std.math.min(240, h.x2.read());
+
+                        // Within X and & bounds, render Win0 Pixel
+                        if (x1 <= x and x < x2) {
+                            if (win0_in) break :blk else continue;
+                        }
+                    }
+                }
+
+                if (win1) {
+                    const h = self.win.h[1];
+                    const v = self.win.v[1];
+
+                    const y1 = v.y1.read();
+                    const y2 = if (y1 > v.y2.read()) 160 else std.math.min(160, v.y2.read());
+
+                    if (y1 <= y and y < y2) {
+                        // Within Y bounds
+                        const x1 = h.x1.read();
+                        const x2 = if (x1 > h.x2.read()) 240 else std.math.min(240, h.x2.read());
+
+                        // Within X and & bounds, render Win1 Pixel
+                        if (x1 <= x and x < x2) {
+                            if (win1_in) break :blk else continue;
+                        }
+                    }
+                }
+
+                // If not Win0 nor Win1 and WinOut isn't enabled,
+                // then don't render this pixel
+                if (!win_out) continue;
+            }
+
             // Grab the Screen Entry from VRAM
             const entry_addr = screen_base + tilemapOffset(size, x, y);
             const entry = @bitCast(ScreenEntry, self.vram.read(u16, entry_addr));
@@ -380,10 +433,10 @@ pub const Ppu = struct {
                 var layer: usize = 0;
                 while (layer < 4) : (layer += 1) {
                     self.drawSprites(@truncate(u2, layer));
-                    if (layer == self.bg[0].cnt.priority.read() and bg_enable & 1 == 1) self.drawBackround(0);
-                    if (layer == self.bg[1].cnt.priority.read() and bg_enable >> 1 & 1 == 1) self.drawBackround(1);
-                    if (layer == self.bg[2].cnt.priority.read() and bg_enable >> 2 & 1 == 1) self.drawBackround(2);
-                    if (layer == self.bg[3].cnt.priority.read() and bg_enable >> 3 & 1 == 1) self.drawBackround(3);
+                    if (layer == self.bg[0].cnt.priority.read() and bg_enable & 1 == 1) self.drawBackground(0);
+                    if (layer == self.bg[1].cnt.priority.read() and bg_enable >> 1 & 1 == 1) self.drawBackground(1);
+                    if (layer == self.bg[2].cnt.priority.read() and bg_enable >> 2 & 1 == 1) self.drawBackground(2);
+                    if (layer == self.bg[3].cnt.priority.read() and bg_enable >> 3 & 1 == 1) self.drawBackground(3);
                 }
 
                 // Copy Drawn Scanline to Frame Buffer
@@ -408,8 +461,8 @@ pub const Ppu = struct {
                 var layer: usize = 0;
                 while (layer < 4) : (layer += 1) {
                     self.drawSprites(@truncate(u2, layer));
-                    if (layer == self.bg[0].cnt.priority.read() and bg_enable & 1 == 1) self.drawBackround(0);
-                    if (layer == self.bg[1].cnt.priority.read() and bg_enable >> 1 & 1 == 1) self.drawBackround(1);
+                    if (layer == self.bg[0].cnt.priority.read() and bg_enable & 1 == 1) self.drawBackground(0);
+                    if (layer == self.bg[1].cnt.priority.read() and bg_enable >> 1 & 1 == 1) self.drawBackground(1);
                     if (layer == self.bg[2].cnt.priority.read() and bg_enable >> 2 & 1 == 1) self.drawAffineBackground(2);
                 }