diff options
Diffstat (limited to 'lib/nes/sys/ppu.cc')
| -rw-r--r-- | lib/nes/sys/ppu.cc | 697 |
1 files changed, 697 insertions, 0 deletions
diff --git a/lib/nes/sys/ppu.cc b/lib/nes/sys/ppu.cc new file mode 100644 index 0000000..2a5f01c --- /dev/null +++ b/lib/nes/sys/ppu.cc @@ -0,0 +1,697 @@ +#include "nes/sys/ppu.hh" +#include "nes/sys/cpu.hh" +#include "nes/sys/cartridge.hh" +#include "nes/sys/types/address.hh" +#include "nes/sys/types/snapshot.hh" +#include "nes/common/display.hh" +#include "nes/common/rgb.hh" +#include "nes/common/debug.hh" + +namespace nes +{ + ppu::ppu(cpu& cpu, cartridge& cartridge, display& display) + : cpu_{ cpu } + , cartridge_{ cartridge } + , display_{ display } + { + } + + auto ppu::build_snapshot(snapshot& snapshot) -> void + { + snapshot.vram = std::vector(std::begin(vram_), std::end(vram_)); + snapshot.oam = std::vector(std::begin(oam_), std::end(oam_)); + } + + auto ppu::step() -> void + { + // See https://www.nesdev.org/wiki/PPU_rendering + // Inspired by https://github.com/fogleman/nes/blob/master/nes/ppu.go + + auto const enable_rendering = mask_.get_enable_background() || mask_.get_enable_sprites(); + + current_cycles_ += cycle_count::from_ppu(1); + scanline_cycle_ += 1; + if (enable_rendering && !even_frame_ && scanline_ == 261 && scanline_cycle_ == 340) + { + current_cycles_ += cycle_count::from_ppu(1); + scanline_cycle_ += 1; + } + if (scanline_cycle_ == 341) + { + scanline_cycle_ = 0; + scanline_ += 1; + + if (scanline_ == 262) + { + scanline_ = 0; + even_frame_ = !even_frame_; + } + } + + auto const pre_line = scanline_ == 261; + auto const visible_line = scanline_ < 240; + auto const render_line = pre_line || visible_line; + auto const pre_fetch_cycle = scanline_cycle_ >= 321 && scanline_cycle_ <= 336; + auto const visible_cycle = scanline_cycle_ >= 1 && scanline_cycle_ <= 256; + auto const fetch_cycle = pre_fetch_cycle || visible_cycle; + + // Background Logic + if (enable_rendering) + { + if (visible_line && visible_cycle) + { + render_pixel(); + } + + if (render_line && fetch_cycle) + { + // Fetch cycle for the background. + switch (scanline_cycle_ % 8) + { + case 1: + { + // Load the tile pattern for the background from the name table. + fetch_cycle_.tile = tile{ read8(address{ 0x2000 } + internal_.v.get_tile_address()) }; + break; + } + case 3: + { + // Load the tile palette for the background from the attribute table. + auto const addr = + address{ 0x23C0 } + + (static_cast<unsigned>(internal_.v.get_name_table()) * 0x400u) + + ((internal_.v.get_coarse_y() & 0b11100u) << 1) + + ((internal_.v.get_coarse_x() & 0b11100u) >> 2); + auto const shift = + ((internal_.v.get_coarse_y() & 0b00010u) << 1) | + ((internal_.v.get_coarse_x() & 0b00010u) << 0); + fetch_cycle_.palette = static_cast<palette>((read8(addr) >> shift) & 0b11); + break; + } + case 5: + { + // Load bitplane 0 for the background tile's pattern. + fetch_cycle_.bitplane_0 = get_tile_bitplane( + control_.get_background_pattern_table(), + fetch_cycle_.tile, + internal_.v.get_fine_y(), + bitplane::_0); + break; + } + case 7: + { + // Load bitplane 1 for the background tile's pattern. + fetch_cycle_.bitplane_1 = get_tile_bitplane( + control_.get_background_pattern_table(), + fetch_cycle_.tile, + internal_.v.get_fine_y(), + bitplane::_1); + break; + } + case 0: + { + // Fetch cycle done -> build the tile row for the background. + current_background_ = next_background_; + next_background_ = get_tile_row( + fetch_cycle_.palette, fetch_cycle_.bitplane_0, fetch_cycle_.bitplane_1); + break; + } + default: + break; + } + } + + if (pre_line && scanline_cycle_ >= 280 && scanline_cycle_ <= 304) + { + copy_y(); + } + + if (render_line) + { + if (fetch_cycle && scanline_cycle_ % 8 == 0) + { + increment_x(); + } + if (scanline_cycle_ == 256) + { + increment_y(); + } + if (scanline_cycle_ == 257) + { + copy_x(); + } + } + } + + // Sprite Logic + if (enable_rendering) + { + if (scanline_cycle_ == 257) + { + if (visible_line) + { + evaluate_sprites(); + } + else + { + sprite_count_ = 0; + } + } + } + + // Vblank Logic + if (scanline_ == 241 && scanline_cycle_ == 1) + { + display_.switch_buffers(); + status_.set_vblank(true); + if (control_.get_vblank_nmi()) { cpu_.trigger_nmi(); } + } + if (pre_line && scanline_cycle_ == 1) + { + status_.set_vblank(false); + status_.set_sprite_zero_hit(false); + status_.set_sprite_overflow(false); + } + } + + auto ppu::render_pixel() -> void + { + auto const x = scanline_cycle_ - 1; + auto const y = scanline_; + + auto background_color = color_index{ 0 }; + if (mask_.get_enable_background()) + { + background_color = current_background_.colors[internal_.x + x % tile_size]; + background_color.set_role(role::background); + } + + auto foreground = evaluated_sprite{}; + auto foreground_color = color_index{ 0 }; + if (mask_.get_enable_sprites()) + { + for (auto i = unsigned{ 0 }; i < sprite_count_; ++i) + { + auto const s = sprites_[i]; + auto const offset = static_cast<int>(x) - static_cast<int>(s.x); + if (offset < 0 || static_cast<unsigned>(offset) >= tile_size) { continue; } + auto const color = s.pattern.colors[offset]; + if (color.get_color() == palette_color::_0) { continue; } + + foreground = s; + foreground_color = color; + foreground_color.set_role(role::foreground); + break; + } + } + + auto has_background = background_color.get_color() != palette_color::_0; + auto has_foreground = foreground_color.get_color() != palette_color::_0; + + if (x < tile_size && !mask_.get_show_background_start()) { has_background = false; } + if (x < tile_size && !mask_.get_show_sprites_start()) { has_foreground = false; } + + auto color = color_index{ 0 }; + if (!has_background && has_foreground) + { + color = foreground_color; + } + if (has_background && !has_foreground) + { + color = background_color; + } + if (has_background && has_foreground) + { + if (foreground.is_sprite_zero && x < 255) + { + status_.set_sprite_zero_hit(true); + } + + color = foreground.is_in_front ? foreground_color : background_color; + } + + display_.set(x, y, resolve_color(ref_color(color))); + } + + auto ppu::evaluate_sprites() -> void + { + auto const height = get_sprite_height(); + sprite_count_ = 0; + for (auto i = unsigned{ 0 }; i < sprite_max_count; ++i) + { + auto const s = sprite{ &oam_[i * 4] }; + auto const row = static_cast<int>(scanline_) - static_cast<int>(s.get_y()); + if (row < 0 || static_cast<unsigned>(row) >= height) { continue; } + + if (sprite_count_ < 8) + { + sprites_[sprite_count_].pattern = fetch_sprite_pattern(s, static_cast<unsigned>(row)); + sprites_[sprite_count_].x = s.get_x(); + sprites_[sprite_count_].is_in_front = !s.get_behind_background(); + sprites_[sprite_count_].is_sprite_zero = i == 0; + sprite_count_ += 1; + } + else + { + status_.set_sprite_overflow(true); + break; + } + } + } + + auto ppu::fetch_sprite_pattern(sprite const s, unsigned row) -> tile_row + { + if (s.get_flip_vertical()) { row = get_sprite_height() - 1 - row; } + tile tile; + pattern_table pattern_table; + switch (control_.get_sprite_size()) + { + case sprite_size::single_height: + tile = s.get_small_tile(); + pattern_table = control_.get_sprite_pattern_table(); + break; + case sprite_size::double_height: + tile = s.get_large_top_tile(); + if (row >= tile_size) + { + tile = static_cast<ppu::tile>(1); + row -= tile_size; + } + pattern_table = s.get_large_pattern_table(); + break; + default: + return tile_row{}; + } + + auto const bitplane_0 = get_tile_bitplane(pattern_table, tile, row, bitplane::_0); + auto const bitplane_1 = get_tile_bitplane(pattern_table, tile, row, bitplane::_1); + auto res = get_tile_row(s.get_palette(), bitplane_0, bitplane_1); + + if (s.get_flip_horizontal()) + { + for (auto i = unsigned{ 0 }; i < tile_size / 2; ++i) + { + std::swap(res.colors[i], res.colors[tile_size - 1 - i]); + } + } + + return res; + } + + // ----------------------------------------------------------------------------------------------------------------- + // Memory Access + // ----------------------------------------------------------------------------------------------------------------- + + // + // See: https://www.nesdev.org/wiki/PPU_memory_map + // + + auto ppu::read8(address addr) -> std::uint8_t + { + addr = addr % 0x4000; // PPU only has 16 KiB addresses. + if (addr <= address{ 0x3EFF }) { return cartridge_.get_mapper().read_ppu(addr, cartridge_, vram_); } + if (addr <= address{ 0x3FFF }) + { + auto const index = color_index{ static_cast<std::uint8_t>(addr.get_absolute() % 0x20) }; + auto const color = ref_color(index); + return static_cast<std::uint8_t>(color); + } + + return 0x0; + } + + auto ppu::write8(address addr, std::uint8_t const value) -> void + { + addr = addr % 0x4000; // PPU only has 16 KiB addresses. + if (addr <= address{ 0x3EFF }) + { + cartridge_.get_mapper().write_ppu(addr, value, cartridge_, vram_); + return; + } + if (addr <= address{ 0x3FFF }) + { + auto const index = color_index{ static_cast<std::uint8_t>(addr.get_absolute() % 0x20) }; + ref_color(index) = color{ value }; + return; + } + } + + // ----------------------------------------------------------------------------------------------------------------- + // IO Registers + // ----------------------------------------------------------------------------------------------------------------- + + // + // See: https://www.nesdev.org/wiki/PPU_registers + // + + auto ppu::read_latch() -> std::uint8_t + { + return latch_; + } + + auto ppu::read_ppustatus() -> std::uint8_t + { + auto res = status_; + res.set_remaining(latch_); + NES_DEBUG_LOG(ppu, "PPUSTATUS -> {:#2x}", res.value); + + status_.set_vblank(false); + internal_.w = false; + + write_latch(res.value); + return res.value; + } + + auto ppu::read_oamdata() -> std::uint8_t + { + auto res = oam_[oamaddr_]; + if ((oamaddr_ & 0x3) == 0x2) + { + res &= 0xE3; + } + NES_DEBUG_LOG(ppu, "OAMDATA -> {:#2x}", res); + write_latch(res); + return res; + } + + auto ppu::read_ppudata() -> std::uint8_t + { + auto const addr = address{ internal_.v.value }; + auto res = read8(addr); + write_latch(ppudata_read_buffer_); + + if (addr % 0x4000 <= address{ 0x3EFF }) + { + std::swap(res, ppudata_read_buffer_); + } + else + { + // For palette buffers: buffer the mirrored nametable instead. + ppudata_read_buffer_ = read8(addr - 0x1000); + } + + NES_DEBUG_LOG(ppu, "PPUDATA -> {:#2x} (address: {:#4x})", res, internal_.v); + increment_vram(); + return res; + } + + auto ppu::write_latch(std::uint8_t const value) -> void + { + latch_ = value; + } + + auto ppu::write_ppuctrl(std::uint8_t const value) -> void + { + write_latch(value); + if (current_cycles_ > boot_up_cycles) + { + NES_DEBUG_LOG(ppu, "PPUCTRL <- {:#2x}", value); + control_.value = value; + internal_.t.set_name_table(control_.get_base_name_table()); + if (control_.get_vblank_nmi() && status_.get_vblank()) { cpu_.trigger_nmi(); } + } + } + + auto ppu::write_ppuscroll(std::uint8_t const value) -> void + { + write_latch(value); + if (current_cycles_ > boot_up_cycles) + { + NES_DEBUG_LOG(ppu, "PPUSCROLL <- {:#2x}", value); + if (!internal_.w) + { + // First write -> x value. + internal_.t.set_coarse_x((value & 0b11111000) >> 3); + internal_.x = (value & 0b00000111) >> 0; + } + else + { + // Second write -> y value. + internal_.t.set_coarse_y((value & 0b11111000) >> 3); + internal_.t.set_fine_y((value & 0b00000111) >> 0); + } + + internal_.w = !internal_.w; + } + } + + auto ppu::write_ppumask(std::uint8_t const value) -> void + { + write_latch(value); + if (current_cycles_ > boot_up_cycles) + { + NES_DEBUG_LOG(ppu, "PPUMASK <- {:#2x}", value); + mask_.value = value; + } + } + + auto ppu::write_ppuaddr(std::uint8_t const value) -> void + { + write_latch(value); + if (current_cycles_ > boot_up_cycles) + { + NES_DEBUG_LOG(ppu, "PPUADDR <- {:#2x}", value); + if (!internal_.w) + { + // First write. + internal_.t.set_address_high(value & 0b00111111); + } + else + { + // Second write. + internal_.t.set_address_low(value); + internal_.v = internal_.t; + } + + internal_.w = !internal_.w; + } + } + + auto ppu::write_ppudata(std::uint8_t const value) -> void + { + NES_DEBUG_LOG(ppu, "PPUDATA <- {:#2x} (address: {:#4x})", value, internal_.v); + write_latch(value); + write8(address{ internal_.v.value }, value); + increment_vram(); + } + + auto ppu::write_oamaddr(std::uint8_t const value) -> void + { + NES_DEBUG_LOG(ppu, "OAMADDR <- {:#2x}", value); + write_latch(value); + oamaddr_ = value; + } + + auto ppu::write_oamdata(std::uint8_t const value) -> void + { + NES_DEBUG_LOG(ppu, "OAMDATA <- {:#2x}", value); + write_latch(value); + oam_[oamaddr_] = value; + oamaddr_ += 1; + } + + auto ppu::write_oamdma(std::uint8_t const value) -> void + { + NES_DEBUG_LOG(ppu, "OAMDMA <- {:#2x}", value); + auto addr = address{ value, 0x00 }; + for (auto i = unsigned{ 0 }; i < 256; ++i) + { + oam_[oamaddr_] = cpu_.read8(addr); + oamaddr_ += 1; + addr = addr + 1; + } + + auto const stalled_cycles = cycle_count::from_cpu((cpu_.get_cycles().to_cpu() % 2 == 0) ? 513 : 514); + cpu_.stall_cycles(stalled_cycles); + } + + // ----------------------------------------------------------------------------------------------------------------- + // Helpers + // ----------------------------------------------------------------------------------------------------------------- + + auto ppu::increment_vram() -> void + { + switch (control_.get_vram_increment()) + { + case vram_increment::forward: + internal_.v.value += 1; + break; + case vram_increment::downward: + internal_.v.value += 32; + break; + } + } + + auto ppu::increment_x() -> void + { + if (internal_.v.get_coarse_x() == 31) + { + internal_.v.set_coarse_x(0); + internal_.v.set_horizontal_name_table(1 ^ internal_.v.get_horizontal_name_table()); + } + else + { + internal_.v.set_coarse_x(internal_.v.get_coarse_x() + 1); + } + } + + auto ppu::increment_y() -> void + { + if (internal_.v.get_fine_y() == 7) + { + internal_.v.set_fine_y(0); + if (internal_.v.get_coarse_y() == 29) + { + internal_.v.set_coarse_y(0); + internal_.v.set_vertical_name_table(1 ^ internal_.v.get_vertical_name_table()); + } + else if (internal_.v.get_coarse_y() == 31) + { + internal_.v.set_coarse_y(0); + // Nametable not switched + } + else + { + internal_.v.set_coarse_y(internal_.v.get_coarse_y() + 1); + } + } + else + { + internal_.v.set_fine_y(internal_.v.get_fine_y() + 1); + } + } + + auto ppu::copy_x() -> void + { + internal_.v.set_coarse_x(internal_.t.get_coarse_x()); + internal_.v.set_horizontal_name_table(internal_.t.get_horizontal_name_table()); + } + + auto ppu::copy_y() -> void + { + internal_.v.set_coarse_y(internal_.t.get_coarse_y()); + internal_.v.set_fine_y(internal_.t.get_fine_y()); + internal_.v.set_vertical_name_table(internal_.t.get_vertical_name_table()); + } + + auto ppu::get_sprite_height() const -> unsigned + { + switch (control_.get_sprite_size()) + { + case sprite_size::single_height: + return tile_size; + case sprite_size::double_height: + return tile_size * 2; + } + + return tile_size; + } + + auto ppu::get_tile_bitplane( + pattern_table const pattern_table, tile const tile, unsigned const row, bitplane const bitplane) -> std::uint8_t + { + auto const addr = static_cast<std::uint16_t>( + 0x1000 * static_cast<unsigned>(pattern_table) + 0x10 * static_cast<unsigned>(tile) + row); + return read8(address{ addr } + (static_cast<unsigned>(bitplane) * 8u)); + } + + auto ppu::get_tile_row(palette const palette, std::uint8_t bitplane_0, std::uint8_t bitplane_1) const -> tile_row + { + auto res = tile_row{}; + for (auto i = unsigned{ 0 }; i < tile_size; ++i) + { + auto const bit_0 = (bitplane_0 & 0b10000000u) >> 7; + auto const bit_1 = (bitplane_1 & 0b10000000u) >> 7; + bitplane_0 <<= 1; + bitplane_1 <<= 1; + res.colors[i].set_palette(palette); + res.colors[i].set_color(palette_color{ (bit_1 << 1) | (bit_0 << 0) }); + } + return res; + } + + auto ppu::ref_color(color_index index) -> color& + { + // See https://www.nesdev.org/wiki/PPU_palettes + index.value = index.value % 0x20; + if (index.get_color() == palette_color::_0) + { + // The first color is mirrored between background and foreground palettes. + index.set_role(role::background); + } + return palette_buffer_[index.value]; + } + + auto ppu::resolve_color(color const color) const -> rgb + { + auto const index = static_cast<std::uint8_t>(color); + switch (index & 0x3F) + { + case 0x00: return rgb::from_hex(0x666666); + case 0x01: return rgb::from_hex(0x002A88); + case 0x02: return rgb::from_hex(0x1412A7); + case 0x03: return rgb::from_hex(0x3B00A4); + case 0x04: return rgb::from_hex(0x5C007E); + case 0x05: return rgb::from_hex(0x6E0040); + case 0x06: return rgb::from_hex(0x6C0600); + case 0x07: return rgb::from_hex(0x561D00); + case 0x08: return rgb::from_hex(0x333500); + case 0x09: return rgb::from_hex(0x0B4800); + case 0x0A: return rgb::from_hex(0x005200); + case 0x0B: return rgb::from_hex(0x004F08); + case 0x0C: return rgb::from_hex(0x00404D); + case 0x0D: return rgb::from_hex(0x000000); + case 0x0E: return rgb::from_hex(0x000000); + case 0x0F: return rgb::from_hex(0x000000); + case 0x10: return rgb::from_hex(0xADADAD); + case 0x11: return rgb::from_hex(0x155FD9); + case 0x12: return rgb::from_hex(0x4240FF); + case 0x13: return rgb::from_hex(0x7527FE); + case 0x14: return rgb::from_hex(0xA01ACC); + case 0x15: return rgb::from_hex(0xB71E7B); + case 0x16: return rgb::from_hex(0xB53120); + case 0x17: return rgb::from_hex(0x994E00); + case 0x18: return rgb::from_hex(0x6B6D00); + case 0x19: return rgb::from_hex(0x388700); + case 0x1A: return rgb::from_hex(0x0C9300); + case 0x1B: return rgb::from_hex(0x008F32); + case 0x1C: return rgb::from_hex(0x007C8D); + case 0x1D: return rgb::from_hex(0x000000); + case 0x1E: return rgb::from_hex(0x000000); + case 0x1F: return rgb::from_hex(0x000000); + case 0x20: return rgb::from_hex(0xFFFEFF); + case 0x21: return rgb::from_hex(0x64B0FF); + case 0x22: return rgb::from_hex(0x9290FF); + case 0x23: return rgb::from_hex(0xC676FF); + case 0x24: return rgb::from_hex(0xF36AFF); + case 0x25: return rgb::from_hex(0xFE6ECC); + case 0x26: return rgb::from_hex(0xFE8170); + case 0x27: return rgb::from_hex(0xEA9E22); + case 0x28: return rgb::from_hex(0xBCBE00); + case 0x29: return rgb::from_hex(0x88D800); + case 0x2A: return rgb::from_hex(0x5CE430); + case 0x2B: return rgb::from_hex(0x45E082); + case 0x2C: return rgb::from_hex(0x48CDDE); + case 0x2D: return rgb::from_hex(0x4F4F4F); + case 0x2E: return rgb::from_hex(0x000000); + case 0x2F: return rgb::from_hex(0x000000); + case 0x30: return rgb::from_hex(0xFFFEFF); + case 0x31: return rgb::from_hex(0xC0DFFF); + case 0x32: return rgb::from_hex(0xD3D2FF); + case 0x33: return rgb::from_hex(0xE8C8FF); + case 0x34: return rgb::from_hex(0xFBC2FF); + case 0x35: return rgb::from_hex(0xFEC4EA); + case 0x36: return rgb::from_hex(0xFECCC5); + case 0x37: return rgb::from_hex(0xF7D8A5); + case 0x38: return rgb::from_hex(0xE4E594); + case 0x39: return rgb::from_hex(0xCFEF96); + case 0x3A: return rgb::from_hex(0xBDF4AB); + case 0x3B: return rgb::from_hex(0xB3F3CC); + case 0x3C: return rgb::from_hex(0xB5EBF2); + case 0x3D: return rgb::from_hex(0xB8B8B8); + case 0x3E: return rgb::from_hex(0x000000); + case 0x3F: return rgb::from_hex(0x000000); + default: return rgb::from_hex(0x000000); + } + } +} // namespace nes
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