Fix collision check bounds

src/sdl_render.c

@@ -224,11 +224,10 @@ static void render_background_line(const nes_ppu* ppu, int line,
         );
 }
 
-static int render_sprite(nes_ppu* ppu, int index,
+static void render_sprite(nes_ppu* ppu, int index,
                           const uint8_t* pal, Render_Mode mode,
                           void* loc, int pitch,
                           const void* back_loc, int back_pitch) {
-    int hit_pos = -1;
     uint8_t* sprite = &ppu->chr_mem[index * 16U];
     uint8_t* dst_line = (uint8_t*)loc;
     const uint8_t* back_line = (uint8_t*)back_loc;
@@ -254,15 +253,6 @@ static int render_sprite(nes_ppu* ppu, int index,
             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) &&
-                    (mode & Render_Mode_Collide) &&
-                    nes_pal_idx != 0xFFU &&
-                    *back != 0xFFU ) {
-                hit_pos = (8 - x) + (8 * (8 - y));
-            }
-*/
             if ((mode & Render_Mode_Behind) && *back != 0xFFU) {
                 nes_pal_idx = 0xFFU;
             }
@@ -276,7 +266,6 @@ static int render_sprite(nes_ppu* ppu, int index,
         back_line += back_pitch;
         ++sprite;
     }
-    return hit_pos;
 }
 
 typedef struct {
@@ -382,13 +371,8 @@ static void render_sprites(nes_ppu* ppu,
         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);
-        if (hit_pos >= 0) {
-            ppu->hit_line = y + (hit_pos / 8);
-            ppu->hit_dot = sprite->x + (hit_pos % 8);
-        }
+        render_sprite(ppu, index, pal, mode, dst, pitch,
+                      dst_back, back_pitch);
 
         SDL_Rect target_rect = {
             .x = sprite->x,
@@ -405,27 +389,29 @@ static void update_sprite_hit(nes_ppu* ppu,
                               const void* back_line,
                               int back_pitch) {
     const oam_sprite* sprite = (oam_sprite*)ppu->oam;
-    int line = (ppu->scanline - nes_ppu_prerender) / 8U;
+    int block_line = (ppu->scanline - nes_ppu_prerender) / 8U;
     int x_fine = ppu->scroll_x % 8;
     int index = sprite->index;
     if (ppu->control & ppu_Control_Sprite_Bank) {
         index += 0x100U;
     }
     const uint8_t* chr = &ppu->chr_mem[index * 16U];
-    int render_line = ppu->scanline - nes_ppu_prerender;
-    if (    ppu->hit_dot == 0 &&
-            (sprite->y + 1) + 7 >= render_line &&
-            (sprite->y + 1) - 7 <= render_line) {
+    int render_line = block_line * 8U;
+    int start_y = (sprite->y + 1) - render_line;
+    int end_y = start_y + 8;
+    if (start_y < 8 && end_y > 0) {
+        if (start_y < 0) start_y = 0;
+        if (end_y > 8) end_y = 8;
         int hit = -1;
         const uint8_t* back = (uint8_t*)back_line + x_fine;
-        back += 8U * line * back_pitch;
-        for (int y = 0; y < 8; ++y) {
+        back += (render_line + start_y) * back_pitch;
+        for (int y = start_y; y < end_y; ++y) {
             hit = eval_sprite_line(
-                    ppu, ppu->scanline + y,
+                    ppu, render_line + y,
                     sprite, chr, back
                 );
             if (hit >= 0) {
-                ppu->hit_line = ppu->scanline + y;
+                ppu->hit_line = y + render_line;
                 ppu->hit_dot = hit;
                 break;
             }