path: root/ppu.c

static uint8_t memory_read_dma(struct nes_state *state, uint32_t offset);

static void ppu_reset(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	__builtin_memset(ppu, 0, sizeof(struct ppu_state));
	ppu->scanline = 261;

}

static uint32_t nt_mirror(uint8_t mode, uint32_t addr) {
	addr &= 0x0fff;
	uint32_t table = addr / 0x400;
	uint32_t offset = addr & 0x03ff;

	switch(mode) {
		case 0: // Horizontal (A A B B)
			if(table == 0 || table == 1) return offset;
			return offset + 0x400;
		case 1: // Vertical (A B A B)
			return (table & 1) * 0x400 + offset;
		case 2: // 1-screen lower
			return offset;
		case 3: // 1-screen upper
			return offset + 0x400;
		case 4: // 4-screen (unsupported in base PPU logic)
		default:
			return addr;
	}
}

static uint32_t palette_mirror(uint32_t addr) {
	addr &= 0x1f;
	if((addr & 0x13) == 0x10) {
		addr &= ~0x10;
	}
	return addr;
}

static uint8_t ppu_read_mem(struct nes_state *state, uint32_t addr) {
	struct ppu_state *ppu = &state->ppu;
	addr &= 0x3fff;

	if(addr < 0x2000) {
		return state->chrrom[addr];
	} else if(addr < 0x3f00) {
		uint32_t nt_index = addr - 0x2000;
		uint32_t mirrored = nt_mirror(state->ines.mirroring, nt_index);
		return ppu->vram[mirrored];
	} else {
		uint32_t mirrored = palette_mirror(addr);
		return ppu->palette[mirrored];
	}
}

static void ppu_write_mem(struct nes_state *state, uint32_t addr, uint8_t value) {
	struct ppu_state *ppu = &state->ppu;

	addr &= 0x3fff;

	if(addr < 0x2000) {
		return; // CHR ROM is read-only
	} else if(addr < 0x3f00) {
		uint32_t mirrored = nt_mirror(state->ines.mirroring, addr - 0x2000);
		ppu->vram[mirrored] = value;
	} else {
		ppu->palette[palette_mirror(addr)] = value;
	}
}


static void ppu_write_2000(struct nes_state *state, uint8_t value) {
	struct ppu_state *ppu = &state->ppu;

	ppu->control = value;
	ppu->nt_x_offset = (value & 0x01) ? 0x400 : 0;
	ppu->nt_y_offset = (value & 0x02) ? 0x800 : 0;
	// printf("write 0x2000 %d\n", value);
}

static void ppu_write_2001(struct nes_state *state, uint8_t value) {
	state->ppu.mask = value;
	// printf("PPU $2001 write: %02x (BG: %s, SPR: %s)\n", value, (value & 0x08) ? "on" : "off", (value & 0x10) ? "on" : "off");
}

static void ppu_write_2003(struct nes_state *state, uint8_t value) {
	state->ppu.oam_addr = value;
	// printf("write 0x2003 %d\n", value);
}

static void ppu_write_2004(struct nes_state *state, uint8_t value) {
	state->ppu.oam[state->ppu.oam_addr] = value;
	state->ppu.oam_addr++;
	// printf("write 0x2004 %d\n", value);
}

static void ppu_write_2005(struct nes_state *state, uint8_t value) {
	struct ppu_state *ppu = &state->ppu;

	printf("2005 write at sc=%u dot=%u: %02x\n", ppu->scanline, ppu->dot, value);

	if(ppu->write_latch == 0) {
		ppu->fine_x = value & 0x07;
		ppu->vram_addr = (ppu->vram_addr & ~0x001f) | ((value >> 3) & 0x1f);
		ppu->write_latch = 1;
	} else {
		uint32_t coarse_y = (value >> 3) & 0x1f;
		uint32_t fine_y = value & 0x07;
		uint32_t nt_y = (value & 0x80) ? 0x800 : 0;

		// Bits 5–9: coarse Y, bit 11: nt_y, bits 12–14: fine Y
		ppu->vram_addr = (ppu->vram_addr & ~0x7be0) | (coarse_y << 5) | nt_y | (fine_y << 12);
		ppu->write_latch = 0;
	}
}

static void ppu_write_2006(struct nes_state *state, uint8_t value) {
	struct ppu_state *ppu = &state->ppu;

	printf("2006 write at sc=%u dot=%u: %02x\n", ppu->scanline, ppu->dot, value);

	if(ppu->write_latch == 0) {
		ppu->vram_addr = ((uint32_t)(value & 0x3f)) << 8;
		ppu->write_latch = 1;
	} else {
		ppu->vram_addr |= value;
		ppu->write_latch = 0;
	}
}

static void ppu_write_2007(struct nes_state *state, uint8_t value) {
	struct ppu_state *ppu = &state->ppu;
	// printf("PPU $2007 write: addr=%04x val=%02x\n", ppu->vram_addr, value);

	ppu_write_mem(state, ppu->vram_addr, value);

// printf("w%04x:%02x cx=%u cy=%u fx=%u ntx=%x nty=%x ", ppu->vram_addr, value, ppu->coarse_x, ppu->coarse_y, ppu->fine_x, ppu->nt_x_offset, ppu->nt_y_offset);

	ppu->vram_addr += (ppu->control & 0x04) ? 32 : 1;
	ppu->vram_addr &= 0x3fff;
}

static uint8_t ppu_read_2002(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	uint8_t result = ppu->vblank | ppu->sprite_zero_hit | ppu->sprite_overflow;
	// printf("PPU $2002 read at PC=%04x: result=%02x (vblank=%02x)\n", state->cpu.pc, result, ppu->vblank);

	ppu->vblank = 0;
	ppu->write_latch = 0;
	return result;
}

static uint8_t ppu_read_2004(struct nes_state *state) {
	printf("ppu_read_2004\n");
	return state->ppu.oam[state->ppu.oam_addr];
}

static uint8_t ppu_read_2007(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;
	// printf("ppu_read_2007\n");

	uint8_t value = ppu_read_mem(state, ppu->vram_addr);

	ppu->vram_addr += (ppu->control & 0x04) ? 32 : 1;
	ppu->vram_addr &= 0x3fff;
	return value;
}

static void ppu_inc_x(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	ppu->render_coarse_x++;
	if(ppu->render_coarse_x == 32) {
		ppu->render_coarse_x = 0;
		ppu->render_nt_x ^= 0x400;
	}
}

static void ppu_inc_y(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	ppu->render_fine_y++;
	if(ppu->render_fine_y == 8) {
		ppu->render_fine_y = 0;
		ppu->render_coarse_y++;

		if(ppu->render_coarse_y == 30) {
			ppu->render_coarse_y = 0;
			ppu->render_nt_y ^= 0x800;
		}
	}
}


static uint8_t ppu_fetch_name_table(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;
	uint32_t addr = 0x2000 | ppu->render_nt_x | ppu->render_nt_y | (ppu->render_coarse_y << 5) | ppu->render_coarse_x;
	return ppu_read_mem(state, addr);
}

static uint8_t ppu_fetch_attribute(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	uint32_t x = ppu->render_coarse_x;
	uint32_t y = ppu->render_coarse_y;
	uint32_t nt = (ppu->render_nt_y ? 0x800 : 0) | (ppu->render_nt_x ? 0x400 : 0);
	uint32_t addr = 0x23c0 | (nt & 0x0c00) | ((y >> 2) << 3) | (x >> 2);

	return ppu_read_mem(state, addr);
}

static uint8_t ppu_fetch_pattern_lo(struct nes_state *state, uint8_t tile) {
	struct ppu_state *ppu = &state->ppu;
	uint32_t base = (ppu->control & 0x10) ? 0x1000 : 0x0000;
	uint32_t addr = base + tile * 16 + ppu->render_fine_y;
	return ppu_read_mem(state, addr);
}

static uint8_t ppu_fetch_pattern_hi(struct nes_state *state, uint8_t tile) {
	struct ppu_state *ppu = &state->ppu;
	uint32_t base = (ppu->control & 0x10) ? 0x1000 : 0x0000;
	uint32_t addr = base + tile * 16 + ppu->render_fine_y + 8;
	return ppu_read_mem(state, addr);
}

static void ppu_load_background_shifters(struct nes_state *state, uint8_t pattern_lo, uint8_t pattern_hi) {
	struct ppu_state *ppu = &state->ppu;

	ppu->bg_shift_lo = (ppu->bg_shift_lo & 0xff00) | pattern_lo;
	ppu->bg_shift_hi = (ppu->bg_shift_hi & 0xff00) | pattern_hi;

	uint8_t pal = ppu->bg_attribute_latch & 3;
	ppu->attr_shift_lo = (ppu->attr_shift_lo & 0xff00) | ((pal & 1) ? 0xff : 0x00);
	ppu->attr_shift_hi = (ppu->attr_shift_hi & 0xff00) | ((pal & 2) ? 0xff : 0x00);
}

static void ppu_shift_background(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	ppu->bg_shift_lo <<= 1;
	ppu->bg_shift_hi <<= 1;
	ppu->attr_shift_lo <<= 1;
	ppu->attr_shift_hi <<= 1;
}

static void ppu_render_pixel(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	if(!(ppu->mask & 0x08)) {
		return;
	}

	uint32_t x = ppu->dot - 1;
	uint32_t y = ppu->scanline;
	uint8_t shift = 15 - ppu->fine_x;

	uint8_t pattern = ((ppu->bg_shift_hi >> shift) & 1) << 1;
	pattern |= (ppu->bg_shift_lo >> shift) & 1;

	uint8_t attrib = ((ppu->attr_shift_hi >> shift) & 1) << 1;
	attrib |= (ppu->attr_shift_lo >> shift) & 1;

	uint8_t index = (attrib << 2) | pattern;

	uint8_t color_index;
	if(index == 0) {
		color_index = ppu->palette[0];
	} else {
		color_index = ppu->palette[index & 0x1f];
	}

	ppu->pixels[y * 256 + x] = color_index;
}

static void ppu_evaluate_sprites(struct nes_state *state, uint32_t target_scanline) {
	struct ppu_state *ppu = &state->ppu;

	ppu->sprite_count = 0;

	for(uint32_t i = 0; i < 64; i++) {
		uint8_t y = ppu->oam[i * 4 + 0];
		uint8_t height = (ppu->control & 0x20) ? 16 : 8;

		if(target_scanline >= y && target_scanline < y + height) {
			if(ppu->sprite_count < 8) {
				uint8_t *dest = &ppu->secondary_oam[ppu->sprite_count * 4];
				dest[0] = y;
				dest[1] = ppu->oam[i * 4 + 1];
				dest[2] = ppu->oam[i * 4 + 2];
				dest[3] = ppu->oam[i * 4 + 3];
				ppu->sprite_count++;
			} else {
				ppu->sprite_overflow = 0x20;
				break;
			}
		}
	}
}

static uint8_t ppu_fetch_sprite_pattern_lo(struct nes_state *state, uint8_t tile, uint8_t y_offset, uint8_t attr, uint8_t height) {
	uint32_t addr;

	if(height == 16) {
		uint32_t bank = (tile & 1) ? 0x1000 : 0x0000;
		tile &= 0xfe;
		addr = bank | ((tile << 4) + (y_offset & 0x07));
	} else {
		uint32_t base = (state->ppu.control & 0x08) ? 0x1000 : 0x0000;
		addr = base | ((tile << 4) + (y_offset & 0x07));
	}
	return ppu_read_mem(state, addr);
}

static uint8_t ppu_fetch_sprite_pattern_hi(struct nes_state *state, uint8_t tile, uint8_t y_offset, uint8_t attr, uint8_t height) {
	uint32_t addr;

	if(height == 16) {
		uint32_t bank = (tile & 1) ? 0x1000 : 0x0000;
		tile &= 0xfe;
		addr = bank | ((tile << 4) + (y_offset & 0x07) + 8);
	} else {
		uint32_t base = (state->ppu.control & 0x08) ? 0x1000 : 0x0000;
		addr = base | ((tile << 4) + (y_offset & 0x07) + 8);
	}
	return ppu_read_mem(state, addr);
}

static void ppu_render_sprites(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	if(!(ppu->mask & 0x10)) {
		return;
	}

	uint32_t x = ppu->dot - 1;
	uint32_t y = ppu->scanline;
	uint8_t bg_pixel = ppu->pixels[y * 256 + x] & 0x3f;

	for(uint32_t i = 0; i < ppu->sprite_count; i++) {
		uint8_t *spr = &ppu->secondary_oam[i * 4];

		uint8_t sy   = spr[0];
		uint8_t tile = spr[1];
		uint8_t attr = spr[2];
		uint8_t sx   = spr[3];

		uint8_t height = (ppu->control & 0x20) ? 16 : 8;

		if(y < sy || y >= sy + height) {
			continue;
		}
		if(x < sx || x >= sx + 8) {
			continue;
		}

		uint8_t offset_y = y - sy;

		if(attr & 0x80) {
			offset_y = height - 1 - offset_y;
		}

		uint8_t shift = 7 - (x - sx);
		if(attr & 0x40) {
			shift = x - sx;
		}

		uint8_t pattern_lo = ppu_fetch_sprite_pattern_lo(state, tile, offset_y, attr, height);
		uint8_t pattern_hi = ppu_fetch_sprite_pattern_hi(state, tile, offset_y, attr, height);

		uint8_t lo_bit = (pattern_lo >> shift) & 1;
		uint8_t hi_bit = (pattern_hi >> shift) & 1;
		uint8_t spr_pixel = (hi_bit << 1) | lo_bit;

		if(spr_pixel == 0) {
			continue;
		}

		uint8_t palette = (attr & 3) << 2;
		uint8_t color_index = ppu_read_mem(state, 0x3f10 + palette + spr_pixel);

		if(i == 0 && bg_pixel && spr_pixel) {
			ppu->sprite_zero_hit = 0x40;
		}

		if(!(attr & 0x20) || bg_pixel == 0) {
			ppu->pixels[y * 256 + x] = color_index;
		}
	}
}

static void ppu_copy_horizontal_scroll(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;
	uint32_t addr = ppu->vram_addr;
	ppu->render_coarse_x = (addr >> 0) & 0x1f;
	ppu->render_nt_x = (addr & 0x400) ? 0x400 : 0;
}

static void ppu_copy_vertical_scroll(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;
	uint32_t addr = ppu->vram_addr;
	ppu->render_coarse_y = (addr >> 5) & 0x1f;
	ppu->render_fine_y = (addr >> 12) & 0x07;
	ppu->render_nt_y = (addr & 0x800) ? 0x800 : 0;
}

__attribute__((flatten))
static void ppu_tick(struct nes_state *state) {
	struct ppu_state *ppu = &state->ppu;

	uint32_t scanline = ppu->scanline;
	uint32_t dot = ppu->dot;

	if(scanline < 240 || scanline == 261) {
		if((dot >= 1 && dot <= 256) || (dot >= 321 && dot <= 336)) {
			ppu_shift_background(state);

			switch((dot - 1) % 8) {
				case 0:
					ppu->next_tile = ppu_fetch_name_table(state);
					break;
				case 2:
					ppu->next_attr = ppu_fetch_attribute(state);
					break;
				case 4:
					ppu->next_lo = ppu_fetch_pattern_lo(state, ppu->next_tile);
					break;
				case 6:
					ppu->next_hi = ppu_fetch_pattern_hi(state, ppu->next_tile);
					break;
				case 7: {
					uint8_t attr = ppu->next_attr;
					uint8_t shift = ((ppu->render_coarse_y >> 2) & 2) | ((ppu->render_coarse_x >> 1) & 1);
					ppu->bg_attribute_latch = (attr >> (shift * 2)) & 3;
					ppu_load_background_shifters(state, ppu->next_lo, ppu->next_hi);
					break;
				}
			}
			if(dot % 8 == 0) {
				ppu_inc_x(state);
			}
		}

		if(scanline < 240 && dot >= 1 && dot <= 256) {
			ppu_render_pixel(state);
			ppu_render_sprites(state);
		}

		if(dot == 256) {
			ppu_inc_y(state);
		}

		if(dot == 257) {
			ppu_copy_horizontal_scroll(state);
			if(scanline < 240) {
				ppu_evaluate_sprites(state, scanline + 1);
			}
		}

		if(scanline == 261 && dot >= 280) {		// && dot <= 304) {
			ppu_copy_vertical_scroll(state);
		}
	}

	if(scanline == 241 && dot == 1) {
		ppu->vblank = 0x80;
		state->nmi_pending = 1;
		ppu->frame_ready = 1;
	}

	if(scanline == 261 && dot == 1) {
		ppu->vblank = 0;
		ppu->sprite_overflow = 0;
		ppu->sprite_zero_hit = 0;
	}

	ppu->dot++;
	if(ppu->dot == 341) {
		ppu->dot = 0;
		ppu->scanline++;
		if(ppu->scanline == 262) {
			ppu->scanline = 0;
		}
	}
}

static void ppu_dma_4014(struct nes_state *state, uint8_t page) {
	uint32_t base = (uint32_t)page << 8;
	uint32_t i;

	uint32_t idle = (state->cycle & 1) ? 2 : 1;
	while(idle--) {
		ppu_tick(state); ppu_tick(state); ppu_tick(state);
		state->cycle++;
	}

	for(i = 0; i < 256; i++) {
		ppu_tick(state); ppu_tick(state); ppu_tick(state);
		state->cycle++;

		uint8_t val = memory_read_dma(state, base + i);

		ppu_tick(state); ppu_tick(state); ppu_tick(state);
		state->cycle++;

		ppu_write_2004(state, val);
	}
}