Last few optimizations to ppu_render_pixel, down to 1.59ns per pixel

1 files changed, 6 insertions, 5 deletions

diff --git a/ppu.c b/ppu.c
index bab97d5..be22921 100644
--- a/ppu.c
+++ b/ppu.c
@@ -35,7 +35,6 @@ static inline void ppu_evaluate_sprites(struct nes_state *state) {
 				dst[2] = src[2];
 				dst[3] = src[3];
 				ppu->sprite_indexes[n] = i;
-				ppu->sprite_zero_hit_possible |= (i == 0);
 
 				dst += 4;
 				n++;
@@ -115,6 +114,11 @@ static inline void ppu_render_pixel(struct nes_state *state) {
 	uint8_t bg_mask = (ppu->reg_mask & 0x08) ? 0xff : 0x00;
 	uint8_t sp_mask = (ppu->reg_mask & 0x10) ? 0xff : 0x00;
 
+	// uint8_t left_mask = (x >= 8) ? 0xff : 0x00;
+	// bg_mask &= ((ppu->reg_mask & 0x02) ? 0xff : 0x00) | left_mask;
+	// sp_mask &= ((ppu->reg_mask & 0x04) ? 0xff : 0x00) | left_mask;
+
+
 	// Background
 	uint8_t p0 = !!(ppu->bg_shift_pattern_low & bit);
 	uint8_t p1 = !!(ppu->bg_shift_pattern_high & bit);
@@ -151,9 +155,7 @@ static inline void ppu_render_pixel(struct nes_state *state) {
 		case 1: { palette_index = 0x10 | sp_index;	} break;
 		case 2: { palette_index = bg_index;				} break;
 		case 3: {
-			if(sp_zero && ppu->sprite_zero_hit_possible && x < 255) {
-				ppu->reg_status |= 0x40;
-			}
+			ppu->reg_status |= (sp_zero && x < 255) ? 0x40 : 0;		// NOTE(peter): Sprite zero hit!
 			palette_index = (sp_prio) ? bg_index : 0x10 | sp_index;
 		} break;
 	}
@@ -395,7 +397,6 @@ static void ppu_tick(struct nes_state *state) {
 		if(UNLIKELY(scanline == 261) && dot == 1) {
 			ppu->reg_status &= ~0x80;
 			ppu->reg_status &= ~0x40;
-			ppu->sprite_zero_hit_possible = 0;
 		}
 
 		dot++;