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static uint8_t __attribute__((aligned(64))) ppu_bitreverse_lut[256] = {
0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
};
static void ppu_reset(struct nes_state *state) {
struct ppu_state *restrict ppu = &state->ppu;
memset(ppu, 0, sizeof(struct ppu_state));
}
__attribute__((hot))
static void ppu_evaluate_sprites(struct nes_state *state) {
struct ppu_state *restrict ppu = &state->ppu;
uint8_t sprite_height = (ppu->reg_ctrl & 0x20) ? 16 : 8;
uint8_t n = 0;
uint8_t * restrict src = ppu->oam;
uint8_t * restrict dst = ppu->secondary_oam;
for(uint8_t i = 0; i < 64; i++) {
uint8_t y = src[0];
int32_t row = (int32_t)ppu->scanline - y;
if(row >= 0 && row < sprite_height) {
if(n < 8) {
dst[0] = src[0];
dst[1] = src[1];
dst[2] = src[2];
dst[3] = src[3];
ppu->sprite_indexes[n] = i;
dst += 4;
n++;
} else {
ppu->reg_status |= 0x20;
break;
}
}
src += 4;
}
ppu->sprite_count = n;
}
__attribute__((hot))
static void ppu_fetch_sprite_patterns(struct nes_state *state) {
struct ppu_state *restrict ppu = &state->ppu;
uint32_t addr;
uint32_t bank;
uint8_t lsb;
uint8_t msb;
uint8_t * restrict s = ppu->secondary_oam;
uint8_t height = (ppu->reg_ctrl & 0x20) ? 16 : 8;
for(uint8_t i = 0; i < ppu->sprite_count; i++) {
uint8_t y = s[0], tile = s[1], attr = s[2], x = s[3];
uint8_t row = ppu->scanline - y;
row = (attr & 0x80) ? height - 1 - row : row;
if(height == 16) {
bank = (tile & 1) << 12;
tile &= 0xfe;
if(row >= 8) {
tile++;
row -= 8;
}
} else {
bank = (ppu->reg_ctrl & 0x08) << 9;
}
addr = bank + tile * 16 + row;
if(attr & 0x40) {
lsb = ppu_bitreverse_lut[state->mapper.chr_read(state, addr)];
msb = ppu_bitreverse_lut[state->mapper.chr_read(state, addr + 8)];
} else {
lsb = state->mapper.chr_read(state, addr);
msb = state->mapper.chr_read(state, addr + 8);
}
ppu->sprite_shift_lo[i] = lsb;
ppu->sprite_shift_hi[i] = msb;
ppu->sprite_positions[i] = x;
ppu->sprite_priorities[i] = attr & 0x20;
s += 4;
}
}
__attribute__((always_inline, hot))
static inline void ppu_render_pixel(struct nes_state *state) {
struct ppu_state *restrict ppu = &state->ppu;
uint32_t x = ppu->dot - 1;
uint32_t y = ppu->scanline;
uint16_t bit = 0x8000 >> ppu->fine_x;
uint8_t bg_pixel = 0;
uint8_t bg_palette = 0;
uint8_t sp_pixel = 0;
uint8_t sp_palette = 0;
uint8_t sp_prio = 0;
uint8_t sp_zero = 0;
uint8_t show_bg = ppu->reg_mask & 0x08;
uint8_t show_sprites = ppu->reg_mask & 0x10;
uint8_t left_bg = ppu->reg_mask & 0x02;
uint8_t left_sp = ppu->reg_mask & 0x04;
uint8_t bg_mask = (show_bg && (left_bg || x & ~7)) ? 0xff : 0x00;
uint8_t sp_mask = (show_sprites && (left_sp || x & ~7)) ? 0xff : 0x00;
// Background
uint8_t p0 = !!(ppu->bg_shift_pattern_low & bit);
uint8_t p1 = !!(ppu->bg_shift_pattern_high & bit);
uint8_t a0 = !!(ppu->bg_shift_attrib_low & bit);
uint8_t a1 = !!(ppu->bg_shift_attrib_high & bit);
bg_pixel = ((p1 << 1) | p0) & bg_mask;
bg_palette = ((a1 << 1) | a0) & bg_mask;
// Sprite
for(uint8_t i = 0; i < ppu->sprite_count; i++) {
if(ppu->sprite_positions[i]) continue;
uint8_t lo = ppu->sprite_shift_lo[i];
uint8_t hi = ppu->sprite_shift_hi[i];
sp_pixel = (((hi & 0x80) >> 6) | ((lo & 0x80) >> 7)) & sp_mask;
if(!sp_pixel) continue;
sp_palette = ppu->secondary_oam[i * 4 + 2] & 3;
sp_prio = ppu->sprite_priorities[i];
sp_zero = (ppu->sprite_indexes[i] == 0);
break;
}
// Final pixel composition
uint8_t palette_index = 0;
uint8_t bg_index = (bg_palette << 2) + bg_pixel;
uint8_t sp_index = (sp_palette << 2) + sp_pixel;
uint8_t selector = (bg_pixel ? 2 : 0) | (sp_pixel ? 1 : 0);
switch(selector) {
case 0: { palette_index = 0; } break;
case 1: { palette_index = 0x10 | sp_index; } break;
case 2: { palette_index = bg_index; } break;
case 3: {
ppu->reg_status |= (sp_zero && x < 255) ? 0x40 : 0; // NOTE(peter): Sprite zero hit!
palette_index = (sp_prio) ? bg_index : 0x10 | sp_index;
} break;
}
state->pixels[y * 256 + x] = ppu->palette[palette_index]; // NOTE(peter): Add color_emphasis bits (expand palette to 8x).
}
__attribute__((hot, flatten))
static void ppu_tick(struct nes_state *state) {
struct ppu_state *restrict ppu = &state->ppu;
uint32_t dot = ppu->dot;
uint32_t scanline = ppu->scanline;
uint8_t rendering = (ppu->reg_mask & 0x18);
for(uint32_t ppu_loops = 0; ppu_loops < 3; ++ppu_loops) {
if(LIKELY(rendering)) {
switch(scanline) {
case 0 ... 239: {
switch(dot) {
case 256: {
if((ppu->vram_addr & 0x7000) != 0x7000) {
ppu->vram_addr += 0x1000;
} else {
ppu->vram_addr &= ~0x7000;
uint32_t y = (ppu->vram_addr & 0x03e0) >> 5;
if(y == 29) {
y = 0;
ppu->vram_addr ^= 0x0800;
} else if(y == 31) {
y = 0;
} else {
y++;
}
ppu->vram_addr = (ppu->vram_addr & ~0x03e0) | (y << 5);
}
}
__attribute__((fallthrough));
case 1 ... 255: // fallthrough: this is 1->256
ppu_render_pixel(state);
__attribute__((fallthrough));
case 321 ... 336: { // fallthrough: the code below has to run 1->256 + 321->336
// Rendering and tile fetch goes here
if(ppu->reg_mask & 0x10) {
for(uint32_t i = 0; i < ppu->sprite_count; i++) {
if(ppu->sprite_positions[i] > 0) {
ppu->sprite_positions[i]--;
} else {
ppu->sprite_shift_lo[i] <<= 1;
ppu->sprite_shift_hi[i] <<= 1;
}
}
}
ppu->bg_shift_pattern_low <<= 1;
ppu->bg_shift_pattern_high <<= 1;
ppu->bg_shift_attrib_low <<= 1;
ppu->bg_shift_attrib_high <<= 1;
switch(dot % 8) {
case 1: {
uint32_t nt_addr = 0x2000 | (ppu->vram_addr & 0x0fff);
ppu->bg_next_tile_id = state->mapper.ciram_read(state, nt_addr);
} break;
case 3: {
uint32_t attr_addr = 0x23c0 | (ppu->vram_addr & 0x0c00) | ((ppu->vram_addr >> 4) & 0x38) | ((ppu->vram_addr >> 2) & 0x07);
uint8_t attr = state->mapper.ciram_read(state, attr_addr & 0x0fff);
uint8_t shift = ((ppu->vram_addr >> 4) & 4) | (ppu->vram_addr & 2);
ppu->bg_next_tile_attrib = (attr >> shift) & 3;
} break;
case 5: {
uint32_t base = (ppu->reg_ctrl & 0x10) ? 0x1000 : 0x0000;
uint32_t tile = ppu->bg_next_tile_id;
uint32_t fine_y = (ppu->vram_addr >> 12) & 7;
uint32_t addr_lsb = (base + tile * 16 + fine_y) & 0x1fff;
ppu->bg_next_tile_lsb = state->mapper.chr_read(state, addr_lsb);
} break;
case 7: {
uint32_t base = (ppu->reg_ctrl & 0x10) ? 0x1000 : 0x0000;
uint32_t tile = ppu->bg_next_tile_id;
uint32_t fine_y = (ppu->vram_addr >> 12) & 7;
uint32_t addr_msb = (base + tile * 16 + fine_y + 8) & 0x1fff;
ppu->bg_next_tile_msb = state->mapper.chr_read(state, addr_msb);
} break;
case 0: {
ppu->bg_shift_pattern_low = (ppu->bg_shift_pattern_low) | ppu->bg_next_tile_lsb;
ppu->bg_shift_pattern_high = (ppu->bg_shift_pattern_high) | ppu->bg_next_tile_msb;
uint8_t a = ppu->bg_next_tile_attrib;
ppu->bg_shift_attrib_low = (ppu->bg_shift_attrib_low) | ((a & 1) ? 0xff : 0x00);
ppu->bg_shift_attrib_high = (ppu->bg_shift_attrib_high) | ((a & 2) ? 0xff : 0x00);
if((ppu->vram_addr & 0x001f) == 31) {
ppu->vram_addr &= ~0x001f;
ppu->vram_addr ^= 0x0400;
} else {
ppu->vram_addr++;
}
} break;
}
} break;
case 257: { // Sprite evaluation and horizontal vram transfer
ppu->vram_addr = (ppu->vram_addr & ~0x041f) | (ppu->temp_addr & 0x041f);
ppu_evaluate_sprites(state);
} break;
case 340: { // sprite fetch pattern
ppu_fetch_sprite_patterns(state);
} break;
}
} break;
case 261: {
switch(dot) {
case 256: {
if((ppu->vram_addr & 0x7000) != 0x7000) {
ppu->vram_addr += 0x1000;
} else {
ppu->vram_addr &= ~0x7000;
uint32_t y = (ppu->vram_addr & 0x03e0) >> 5;
if(y == 29) {
y = 0;
ppu->vram_addr ^= 0x0800;
} else if(y == 31) {
y = 0;
} else {
y++;
}
ppu->vram_addr = (ppu->vram_addr & ~0x03e0) | (y << 5);
}
}
__attribute__((fallthrough));
case 1 ... 255: __attribute__((fallthrough));
case 321 ... 336: { // Rendering and tile fetch
if(ppu->reg_mask & 0x10) {
for(uint32_t i = 0; i < ppu->sprite_count; i++) {
if(ppu->sprite_positions[i] > 0) {
ppu->sprite_positions[i]--;
} else {
ppu->sprite_shift_lo[i] <<= 1;
ppu->sprite_shift_hi[i] <<= 1;
}
}
}
ppu->bg_shift_pattern_low <<= 1;
ppu->bg_shift_pattern_high <<= 1;
ppu->bg_shift_attrib_low <<= 1;
ppu->bg_shift_attrib_high <<= 1;
switch(dot % 8) {
case 1: {
uint32_t nt_addr = 0x2000 | (ppu->vram_addr & 0x0fff);
ppu->bg_next_tile_id = state->mapper.ciram_read(state, nt_addr);
} break;
case 3: {
uint32_t attr_addr = 0x23c0 | (ppu->vram_addr & 0x0c00) | ((ppu->vram_addr >> 4) & 0x38) | ((ppu->vram_addr >> 2) & 0x07);
uint8_t attr = state->mapper.ciram_read(state, attr_addr & 0x0fff);
uint8_t shift = ((ppu->vram_addr >> 4) & 4) | (ppu->vram_addr & 2);
ppu->bg_next_tile_attrib = (attr >> shift) & 3;
} break;
case 5: {
uint32_t base = (ppu->reg_ctrl & 0x10) ? 0x1000 : 0x0000;
uint32_t tile = ppu->bg_next_tile_id;
uint32_t fine_y = (ppu->vram_addr >> 12) & 7;
uint32_t addr_lsb = (base + tile * 16 + fine_y) & 0x1fff;
ppu->bg_next_tile_lsb = state->mapper.chr_read(state, addr_lsb);
} break;
case 7: {
uint32_t base = (ppu->reg_ctrl & 0x10) ? 0x1000 : 0x0000;
uint32_t tile = ppu->bg_next_tile_id;
uint32_t fine_y = (ppu->vram_addr >> 12) & 7;
uint32_t addr_msb = (base + tile * 16 + fine_y + 8) & 0x1fff;
ppu->bg_next_tile_msb = state->mapper.chr_read(state, addr_msb);
} break;
case 0: {
ppu->bg_shift_pattern_low = (ppu->bg_shift_pattern_low & 0xff00) | ppu->bg_next_tile_lsb;
ppu->bg_shift_pattern_high = (ppu->bg_shift_pattern_high & 0xff00) | ppu->bg_next_tile_msb;
uint8_t a = ppu->bg_next_tile_attrib;
ppu->bg_shift_attrib_low = (ppu->bg_shift_attrib_low & 0xff00) | ((a & 1) ? 0xff : 0x00);
ppu->bg_shift_attrib_high = (ppu->bg_shift_attrib_high & 0xff00) | ((a & 2) ? 0xff : 0x00);
if((ppu->vram_addr & 0x001f) == 31) {
ppu->vram_addr &= ~0x001f;
ppu->vram_addr ^= 0x0400;
} else {
ppu->vram_addr++;
}
} break;
}
} break;
case 257: { // Sprite evaluation and horizontal vram transfer
ppu->vram_addr = (ppu->vram_addr & ~0x041f) | (ppu->temp_addr & 0x041f);
ppu_evaluate_sprites(state);
} break;
case 280 ... 304: { // Vertical vram transfer
ppu->vram_addr = (ppu->vram_addr & ~0x7be0) | (ppu->temp_addr & 0x7be0);
} break;
case 340: { // Sprite pattern fetch
ppu_fetch_sprite_patterns(state);
} break;
}
} break;
}
}
if(UNLIKELY(scanline == 241) && dot == 1) {
// static int32_t tas_frame = 0;
// state->input[0] = tas_input[tas_frame++];
ppu->reg_status |= 0x80;
if(ppu->reg_ctrl & 0x80) {
state->cpu.nmi_pending = 1;
}
}
if(UNLIKELY(scanline == 261) && dot == 1) {
ppu->reg_status &= ~0x80;
ppu->reg_status &= ~0x40;
}
dot++;
if(dot > 340) {
dot = 0;
scanline++;
if(UNLIKELY(scanline == 261 && !ppu->even_frame && (ppu->reg_mask & 0x18))) {
dot = 1;
}
if(scanline > 261) {
scanline = 0;
ppu->frame_ready = 1;
ppu->even_frame = !ppu->even_frame;
}
}
ppu->dot = dot;
ppu->scanline = scanline;
}
}
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