path: root/lib/nes/ppu.hh

#pragma once

#include "nes/util/cycle-count.hh"

namespace nes
{
	class address;
	class cpu;
	class cartridge;
	class display;
	class rgb;
	struct snapshot;

	class ppu
	{
		static constexpr auto sprite_max_count = unsigned{ 64 };
		static constexpr auto vram_size = std::size_t{ 0x800 };
		static constexpr auto oam_size = std::size_t{ sprite_max_count * 4 };
		static constexpr auto palette_buffer_size = std::size_t{ 0x20 };
		static constexpr auto tile_size = unsigned{ 8 };
		// Writes to some registers are ignored until this clock cycle.
		static constexpr auto boot_up_cycles = cycle_count::from_ppu(29658);

		enum class bitplane : unsigned { _0, _1 };
		enum class palette : unsigned { _0, _1, _2, _3 };
		enum class palette_color : unsigned { _0, _1, _2, _3 };
		enum class name_table : unsigned { _0, _1, _2, _3 };
		enum class role : unsigned { background, foreground };
		enum class pattern_table : unsigned { _0, _1 };
		enum class vram_increment : unsigned { forward, downward };
		enum class sprite_size : unsigned { single_height, double_height };
		enum class tile : std::uint8_t {};
		enum class color : std::uint8_t {};

#define BITFIELD_VALIDATE(mask, offset_from_right) \
	static_assert((mask & (1 << offset_from_right)) != 0); \
	static_assert(offset_from_right == 0 || (mask & (1 << (offset_from_right - 1))) == 0);
#define BITFIELD_VALUE(name, base, mask, offset_from_right) \
	BITFIELD_VALIDATE(mask, offset_from_right) \
	auto get_##name() const -> unsigned { return (base & mask) >> offset_from_right; } \
	auto set_##name(unsigned const v) -> void { base = (base & ~mask) | ((v << offset_from_right) & mask); }
#define BITFIELD_ENUM(name, type, base, mask, offset_from_right) \
	BITFIELD_VALIDATE(mask, offset_from_right) \
	auto get_##name() const -> type { return static_cast<type>((base & mask) >> offset_from_right); } \
	auto set_##name(type const v) -> void { base = (base & ~mask) | ((static_cast<unsigned>(v) << offset_from_right) & mask); }
#define BITFIELD_FLAG(name, base, mask, offset_from_right) \
	BITFIELD_VALIDATE(mask, offset_from_right) \
	auto get_##name() const -> bool { return base & mask; } \
	auto set_##name(unsigned const v) -> void { base = (base & ~mask) | (v ? mask : 0); }

		struct color_index
		{
			BITFIELD_ENUM(color, palette_color, value, 0b00000011, 0)
			BITFIELD_ENUM(palette, palette, value, 0b00001100, 2)
			BITFIELD_ENUM(role, role, value, 0b00010000, 4)

			std::uint8_t value{};

			color_index() = default;

			explicit color_index(std::uint8_t const value)
				: value{ value }
			{
			}
		};

		struct sprite
		{
			// Tile index (and pattern table) for sprites
			BITFIELD_ENUM(large_pattern_table, pattern_table, tile_index, 0b00000001, 0)
			BITFIELD_ENUM(large_top_tile, tile, tile_index, 0b11111110, 1)
			BITFIELD_ENUM(small_tile, tile, tile_index, 0b11111111, 0)

			// Attributes
			BITFIELD_ENUM(palette, palette, attributes, 0b00000011, 0)
			BITFIELD_FLAG(behind_background, attributes, 0b00100000, 5)
			BITFIELD_FLAG(flip_horizontal, attributes, 0b01000000, 6)
			BITFIELD_FLAG(flip_vertical, attributes, 0b10000000, 7)

			std::uint8_t y{};
			std::uint8_t tile_index{};
			std::uint8_t attributes{};
			std::uint8_t x{};

			explicit sprite() = default;

			explicit sprite(std::uint8_t const y, std::uint8_t const tile_index, std::uint8_t const attributes, std::uint8_t const x)
				: y{ y }
				, tile_index{ tile_index }
				, attributes{ attributes }
				, x{ x }
			{
			}
		};

		struct tile_row
		{
			color_index colors[tile_size]{};
		};

		struct evaluated_sprite
		{
			tile_row pattern;
			std::uint8_t x{ 0 };
			bool is_in_front{ false };
			bool is_sprite_zero{ false };
		};

		cycle_count current_cycles_;
		cpu& cpu_;
		cartridge& cartridge_;
		display& display_;
		std::uint8_t vram_[vram_size]{};
		std::uint8_t oam_[oam_size]{};
		color palette_buffer_[palette_buffer_size]
		{
			color{ 0x09 }, color{ 0x01 }, color{ 0x00 }, color{ 0x01 },
			color{ 0x00 }, color{ 0x02 }, color{ 0x02 }, color{ 0x0D },
			color{ 0x08 }, color{ 0x10 }, color{ 0x08 }, color{ 0x24 },
			color{ 0x00 }, color{ 0x00 }, color{ 0x04 }, color{ 0x2C },
			color{ 0x09 }, color{ 0x01 }, color{ 0x34 }, color{ 0x03 },
			color{ 0x00 }, color{ 0x04 }, color{ 0x00 }, color{ 0x14 },
			color{ 0x08 }, color{ 0x3A }, color{ 0x00 }, color{ 0x02 },
			color{ 0x00 }, color{ 0x20 }, color{ 0x2C }, color{ 0x08 },
		};
		std::uint8_t latch_{}; // The last read/written IO register value, returned when reading write-only registers.
		struct
		{
			BITFIELD_FLAG(sprite_overflow, value, 0b00100000, 5)
			BITFIELD_FLAG(sprite_zero_hit, value, 0b01000000, 6)
			BITFIELD_FLAG(vblank, value, 0b10000000, 7)

			// Set the remaining (unused) bits based on the given value.
			auto set_remaining(std::uint8_t const v) -> void { value = (value & ~0b00011111) | (v & 0b00011111); }

			std::uint8_t value{ 0b00000000 };
		} status_{};
		struct
		{
			// Base nametable address.
			BITFIELD_ENUM(base_name_table, name_table, value, 0b00000011, 0)
			// How VRAM addresses should be incremented each read/write.
			BITFIELD_ENUM(vram_increment, vram_increment, value, 0b00000100, 2)
			// Sprite pattern table address for 8x8 sprites.
			BITFIELD_ENUM(sprite_pattern_table, pattern_table, value, 0b00001000, 3)
			// Background pattern table address.
			BITFIELD_ENUM(background_pattern_table, pattern_table, value, 0b00010000, 4)
			// The size of the sprites used (i.e. single-height or double-height).
			BITFIELD_ENUM(sprite_size, sprite_size, value, 0b00100000, 5)
			// PPU master/slave select.
			BITFIELD_FLAG(enable_ext_pin, value, 0b01000000, 6)
			// Enable/disable vblank NMI.
			BITFIELD_FLAG(vblank_nmi, value, 0b10000000, 7)

			std::uint8_t value{ 0b00000000 };
		} control_{};
		struct
		{
			// Enable/disable grayscale.
			BITFIELD_FLAG(grayscale, value, 0b00000001, 0)
			// Show background in leftmost 8 pixels of screen.
			BITFIELD_FLAG(show_background_start, value, 0b00000010, 1)
			// Show sprites in leftmost 8 pixels of screen.
			BITFIELD_FLAG(show_sprites_start, value, 0b00000100, 2)
			// Enable background rendering.
			BITFIELD_FLAG(enable_background, value, 0b00001000, 3)
			// Enable sprite rendering.
			BITFIELD_FLAG(enable_sprites, value, 0b00010000, 4)
			// Emphasize red.
			BITFIELD_FLAG(emphasize_red, value, 0b00100000, 5)
			// Emphasize green.
			BITFIELD_FLAG(emphasize_green, value, 0b01000000, 6)
			// Emphasize blue.
			BITFIELD_FLAG(emphasize_blue, value, 0b10000000, 7)

			std::uint8_t value{ 0b00000000 };
		} mask_{};
		struct
		{
			// See https://www.nesdev.org/wiki/PPU_scrolling#PPU_internal_registers
			struct
			{
				// Scroll position
				BITFIELD_VALUE(coarse_x, value, 0b0000000000011111, 0)
				BITFIELD_VALUE(coarse_y, value, 0b0000001111100000, 5)
				BITFIELD_ENUM(name_table, name_table, value, 0b0000110000000000, 10)
				BITFIELD_VALUE(horizontal_name_table, value, 0b0000010000000000, 10)
				BITFIELD_VALUE(vertical_name_table, value, 0b0000100000000000, 11)
				BITFIELD_VALUE(tile_address, value, 0b0000111111111111, 0)
				BITFIELD_VALUE(fine_y, value, 0b0111000000000000, 12)

				// Address
				BITFIELD_VALUE(address_low, value, 0b0000000011111111, 0)
				BITFIELD_VALUE(address_high, value, 0b0111111100000000, 8)

				std::uint16_t value{};
			} v{}, t{}; // Current and temporary VRAM address and scroll position (15 bits)
			std::uint8_t x{}; // Fine X scroll (3 bits)
			bool w{}; // Second write toggle (1 bit)
		} internal_{};
		std::uint8_t oamaddr_{}; // Address accessed by IO registers
		std::uint8_t ppudata_read_buffer_{}; // Delays PPUDATA reads by one.
		unsigned scanline_{ 240 };
		unsigned scanline_cycle_{ 340 };
		bool even_frame_{ true };
		tile_row current_background_{};
		tile_row next_background_{};
		struct
		{
			tile tile{ 0 };
			palette palette{ 0 };
			std::uint8_t bitplane_0{ 0 };
			std::uint8_t bitplane_1{ 0 };
		} fetch_cycle_{}; // Data populated during the fetch cycle.
		evaluated_sprite sprites_[8]{}; // Evaluated sprites.
		unsigned sprite_count_{ 0 }; // Number of evaluated sprites in sprites_.

#undef BITFIELD_VALIDATE
#undef BITFIELD_VALUE
#undef BITFIELD_ENUM
#undef BITFIELD_FLAG

	public:
		explicit ppu(cpu&, cartridge&, display&);

		ppu(ppu const&) = delete;
		ppu(ppu&&) = delete;
		auto operator=(ppu const&) -> ppu& = delete;
		auto operator=(ppu&&) -> ppu& = delete;

		auto get_cycles() const -> cycle_count { return current_cycles_; }
		auto build_snapshot(snapshot&) -> void;
		auto step() -> void;

		// Memory access

		auto read8(address) -> std::uint8_t;
		auto write8(address, std::uint8_t) -> void;

		// IO registers

		auto read_latch() -> std::uint8_t;
		auto read_ppustatus() -> std::uint8_t;
		auto read_oamdata() -> std::uint8_t;
		auto read_ppudata() -> std::uint8_t;

		auto write_latch(std::uint8_t) -> void;
		auto write_ppuctrl(std::uint8_t) -> void;
		auto write_ppuscroll(std::uint8_t) -> void;
		auto write_ppumask(std::uint8_t) -> void;
		auto write_ppuaddr(std::uint8_t) -> void;
		auto write_ppudata(std::uint8_t) -> void;
		auto write_oamaddr(std::uint8_t) -> void;
		auto write_oamdata(std::uint8_t) -> void;
		auto write_oamdma(std::uint8_t) -> void;

	private:
		auto render_pixel() -> void;
		auto evaluate_sprites() -> void;
		auto fetch_sprite_pattern(sprite, unsigned row) -> tile_row;

		// Helpers

		auto increment_vram() -> void;
		auto increment_x() -> void;
		auto increment_y() -> void;
		auto copy_x() -> void;
		auto copy_y() -> void;
		auto get_sprite_height() const -> unsigned;
		auto get_sprite(unsigned i) const -> sprite;
		auto get_tile_bitplane(pattern_table, tile, unsigned row, bitplane) -> std::uint8_t;
		auto get_tile_row(palette, std::uint8_t bitplane_0, std::uint8_t bitplane_1) const -> tile_row;
		auto ref_color(color_index) -> color&;
		auto resolve_color(color) const -> rgb;
	};
} // namespace nes