Add mirroring support to sprite rendering

src/sdl_render.c

@@ -150,10 +150,12 @@ static void sdl_render_done(nes_Renderer* rend) {
 }
 
 typedef enum {
-    Render_Mode_Sprite      = 0b000,
-    Render_Mode_Background  = 0b001,
-    Render_Mode_Behind      = 0b010,
-    Render_Mode_Collide     = 0b100,
+    Render_Mode_Sprite      = 0b00000,
+    Render_Mode_Background  = 0b00001,
+    Render_Mode_Behind      = 0b00010,
+    Render_Mode_Collide     = 0b00100,
+    Render_Mode_Flip_X      = 0b01000,
+    Render_Mode_Flip_Y      = 0b10000,
 } Render_Mode;
 
 
@@ -165,13 +167,23 @@ static int render_sprite(nes_ppu* ppu, int index,
     uint8_t* sprite = &ppu->chr_mem[index * 16U];
     uint8_t* dst_line = (uint8_t*)loc;
     const uint8_t* back_line = (uint8_t*)back_loc;
+    if (mode & Render_Mode_Flip_X) {
+        dst_line += 7;
+        back_line += 7;
+    }
+    if (mode & Render_Mode_Flip_Y) {
+        dst_line += (7 * pitch);
+        back_line += (7 * back_pitch);
+    }
+
     for (int y = 8; y > 0; --y) {
         uint8_t lo = sprite[0U];
         uint8_t hi = sprite[8U];
         uint8_t* dst = dst_line;
         const uint8_t* back = back_line;
         for (int x = 8; x > 0; --x) {
-            int pal_idx = ((hi & 0x80) >> 6) | ((lo & 0x80) >> 7);
+            int pal_idx = ( ((hi & 0x80) >> 6) |
+                            ((lo & 0x80) >> 7));
             int nes_pal_idx = (pal_idx ? pal[pal_idx] : 0xFFU);
             if (    hit_pos < 0 &&
                     (ppu->mask & ppu_Mask_Back) &&
@@ -183,13 +195,24 @@ static int render_sprite(nes_ppu* ppu, int index,
             if ((mode & Render_Mode_Behind) && *back != 0xFFU) {
                 nes_pal_idx = 0xFFU;
             }
-            *dst++ = nes_pal_idx;
-            ++back;
+            *dst = nes_pal_idx;
+            if (mode & Render_Mode_Flip_X) {
+                dst--;
+                back--;
+            } else {
+                dst++;
+                back++;
+            }
             hi <<= 1;
             lo <<= 1;
         }
-        dst_line += pitch;
-        back_line += back_pitch;
+        if (mode & Render_Mode_Flip_Y) {
+            dst_line -= pitch;
+            back_line -= back_pitch;
+        } else {
+            dst_line += pitch;
+            back_line += back_pitch;
+        }
         ++sprite;
     }
     return hit_pos;
@@ -273,13 +296,18 @@ static void render_sprites(nes_ppu* ppu,
         const uint8_t* dst_back = back_offset + back_origin;
         // TODO: Support 8x16 sprites
         int index = bank + sprite->index;
-        // TODO: Support mirroring
         int pal_idx = (sprite->attr & oam_Attr_Pal_Mask);
         const uint8_t* pal = &ppu->palette[16 + (pal_idx * 4)];
         Render_Mode mode = (sprite->attr & oam_Attr_Background) ?
                            Render_Mode_Behind :
                            Render_Mode_Sprite;
         if (i_sprite == 0) mode |= Render_Mode_Collide;
+        if (sprite->attr & oam_Attr_Flip_X) {
+            mode |= Render_Mode_Flip_X;
+        }
+        if (sprite->attr & oam_Attr_Flip_Y) {
+            mode |= Render_Mode_Flip_Y;
+        }
         int hit_pos = render_sprite(ppu, index, pal, mode,
                                     dst, pitch,
                                     dst_back, back_pitch);