CLK/Machines/PCCompatible/CGA.hpp

//
//  CGA.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 05/12/2023.
//  Copyright © 2023 Thomas Harte. All rights reserved.
//

#pragma once

#include "../../Components/6845/CRTC6845.hpp"
#include "../../Outputs/CRT/CRT.hpp"
#include "../../Machines/Utility/ROMCatalogue.hpp"

namespace PCCompatible {

class CGA {
	public:
		CGA() : crtc_(outputter_) {}

		static constexpr uint32_t BaseAddress = 0xb'8000;
		static constexpr auto FontROM = ROM::Name::PCCompatibleCGAFont;

		void set_source(const uint8_t *ram, std::vector<uint8_t> font) {
			outputter_.ram = ram;
			outputter_.font = font;
		}

		void run_for(Cycles cycles) {
			// Input rate is the PIT rate of 1,193,182 Hz.
			// CGA is clocked at the real oscillator rate of 12 times that.
			// But there's also an internal divide by 8 to align to the 80-cfetch clock.
			// ... and 12/8 = 3/2.
			full_clock_ += 3 * cycles.as<int>();

			const int modulo = 2 * outputter_.clock_divider;
			crtc_.run_for(Cycles(full_clock_ / modulo));
			full_clock_ %= modulo;
		}

		template <int address>
		void write(uint8_t value) {
			switch(address) {
				case 0:	case 2:	case 4:	case 6:
					crtc_.select_register(value);
				break;
				case 1:	case 3:	case 5:	case 7:
					crtc_.set_register(value);
				break;

				case 0x8:	outputter_.set_mode(value);		break;
				case 0x9:	outputter_.set_colours(value);	break;
			}
		}

		template <int address>
		uint8_t read() {
			switch(address) {
				case 1:	case 3:	case 5:	case 7:
					return crtc_.get_register();

				case 0xa:
					return
						// b3: 1 => in vsync; 0 => not;
						// b2: 1 => light pen switch is off;
						// b1: 1 => positive edge from light pen has set trigger;
						// b0: 1 => safe to write to VRAM now without causing snow.
						(crtc_.get_bus_state().vsync ? 0b1001 : 0b0000) |
						(crtc_.get_bus_state().display_enable ? 0b0000 : 0b0001) |
						0b0100;

				default: return 0xff;
			}
		}

		// MARK: - Display type configuration.

		void set_display_type(Outputs::Display::DisplayType display_type) {
			outputter_.crt.set_display_type(display_type);
			outputter_.set_is_composite(Outputs::Display::is_composite(display_type));
		}
		Outputs::Display::DisplayType get_display_type() const {
			return outputter_.crt.get_display_type();
		}

		// MARK: - Call-ins for ScanProducer.

		void set_scan_target(Outputs::Display::ScanTarget *scan_target) {
			outputter_.crt.set_scan_target(scan_target);
		}
		Outputs::Display::ScanStatus get_scaled_scan_status() const {
			// The CRT is always handed data at the full CGA pixel clock rate, so just
			// divide by 12 to get back to the rate that run_for is being called at.
			return outputter_.crt.get_scaled_scan_status() / 12.0f;
		}

	private:
		struct CRTCOutputter {
			enum class OutputState {
				Sync, Pixels, Border, ColourBurst
			};

			CRTCOutputter() :
				crt(910, 8, Outputs::Display::Type::NTSC60, Outputs::Display::InputDataType::Red2Green2Blue2)
			{
				crt.set_visible_area(Outputs::Display::Rect(0.097f, 0.095f, 0.82f, 0.82f));
				crt.set_display_type(Outputs::Display::DisplayType::RGB);
			}

			void set_mode(uint8_t control) {
				// b5: enable blink
				// b4: 1 => 640x200 graphics
				// b3: video enable
				// b2: 1 => monochrome
				// b1: 1 => 320x200 graphics; 0 => text
				// b0: 1 => 80-column text; 0 => 40

				control_ = control;	// To capture blink, monochrome and video enable bits.

				if(control & 0x2) {
					mode_ = (control & 0x10) ? Mode::Pixels640 : Mode::Pixels320;
					pixels_per_tick = (mode_ == Mode::Pixels640) ? 16 : 8;
				} else {
					mode_ = Mode::Text;
					pixels_per_tick = 8;
				}
				clock_divider = 1 + !(control & 0x01);

				// Both graphics mode and monochrome/colour may have changed, so update the palette.
				update_palette();
			}

			void set_is_composite(bool is_composite) {
				is_composite_ = is_composite;
				update_palette();
			}

			void set_colours(uint8_t value) {
				colours_ = value;
				update_palette();
			}

			uint8_t control() {
				return control_;
			}

			void update_hsync(bool new_hsync) {
				if(new_hsync == previous_hsync) {
					cycles_since_hsync += clock_divider;
				} else {
					cycles_since_hsync = 0;
					previous_hsync = new_hsync;
				}
			}

			OutputState implied_state(const Motorola::CRTC::BusState &state) const {
				OutputState new_state;

				if(state.hsync || state.vsync) {
					new_state = OutputState::Sync;
				} else if(!state.display_enable || !(control_&0x08)) {
					new_state = OutputState::Border;

					// TODO: this isn't correct for colour burst positioning, though
					// it happens to fool the particular CRT I've implemented.
					if(!(control_&4) && cycles_since_hsync <= 6) {
						new_state = OutputState::ColourBurst;
					}
				} else {
					new_state = OutputState::Pixels;
				}

				return new_state;
			}

			void perform_bus_cycle_phase1(const Motorola::CRTC::BusState &state) {
				// Determine new output state.
				update_hsync(state.hsync);
				const OutputState new_state = implied_state(state);
				static constexpr uint8_t colour_phase = 200;

				// Upon either a state change or just having accumulated too much local time...
				if(
					new_state != output_state ||
					active_pixels_per_tick != pixels_per_tick ||
					active_clock_divider != clock_divider ||
					active_border_colour != border_colour ||
					count > 912
				) {
					// (1) flush preexisting state.
					if(count) {
						switch(output_state) {
							case OutputState::Sync:			crt.output_sync(count * active_clock_divider);							break;
							case OutputState::Border:
								if(active_border_colour) {
									crt.output_blank(count * active_clock_divider);
								} else {
									crt.output_level<uint8_t>(count * active_clock_divider, active_border_colour);
								}
							break;
							case OutputState::ColourBurst:	crt.output_colour_burst(count * active_clock_divider, colour_phase);	break;
							case OutputState::Pixels:		flush_pixels();															break;
						}
					}

					// (2) adopt new state.
					output_state = new_state;
					active_pixels_per_tick = pixels_per_tick;
					active_clock_divider = clock_divider;
					active_border_colour = border_colour;
					count = 0;
				}

				// Collect pixels if applicable.
				if(output_state == OutputState::Pixels) {
					if(!pixels) {
						pixel_pointer = pixels = crt.begin_data(DefaultAllocationSize);

						// Flush any period where pixels weren't recorded due to back pressure.
						if(pixels && count) {
							crt.output_blank(count * active_clock_divider);
							count = 0;
						}
					}

					if(pixels) {
						if(state.cursor) {
							std::fill(pixel_pointer, pixel_pointer + pixels_per_tick, 0x3f); // i.e. white.
						} else {
							if(mode_ == Mode::Text) {
								serialise_text(state);
							} else {
								serialise_pixels(state);
							}
						}
						pixel_pointer += active_pixels_per_tick;
					}
				}

				// Advance.
				count += 8;

				// Output pixel row prematurely if storage is exhausted.
				if(output_state == OutputState::Pixels && pixel_pointer == pixels + DefaultAllocationSize) {
					flush_pixels();
					count = 0;
				}
			}
			void perform_bus_cycle_phase2(const Motorola::CRTC::BusState &) {}

			void flush_pixels() {
				crt.output_data(count * active_clock_divider, size_t((count * active_pixels_per_tick) / 8));
				pixels = pixel_pointer = nullptr;
			}

			void serialise_pixels(const Motorola::CRTC::BusState &state) {
				// This is what I think is happenings:
				//
				// Refresh address is still shifted left one and two bytes are fetched, just as if it were
				// character code + attributes except that these are two bytes worth of graphics.
				//
				// Meanwhile, row address is used to invent a 15th address line.
				const auto base_address =
					((state.refresh_address & 0xfff) << 1) +
					((state.row_address & 1) << 13);
				const uint8_t bitmap[] = {
					ram[base_address],
					ram[base_address + 1],
				};

				if(mode_ == Mode::Pixels320) {
					pixel_pointer[0] = palette320[(bitmap[0] & 0xc0) >> 6];
					pixel_pointer[1] = palette320[(bitmap[0] & 0x30) >> 4];
					pixel_pointer[2] = palette320[(bitmap[0] & 0x0c) >> 2];
					pixel_pointer[3] = palette320[(bitmap[0] & 0x03) >> 0];
					pixel_pointer[4] = palette320[(bitmap[1] & 0xc0) >> 6];
					pixel_pointer[5] = palette320[(bitmap[1] & 0x30) >> 4];
					pixel_pointer[6] = palette320[(bitmap[1] & 0x0c) >> 2];
					pixel_pointer[7] = palette320[(bitmap[1] & 0x03) >> 0];
				} else {
					pixel_pointer[0x0] = palette640[(bitmap[0] & 0x80) >> 7];
					pixel_pointer[0x1] = palette640[(bitmap[0] & 0x40) >> 6];
					pixel_pointer[0x2] = palette640[(bitmap[0] & 0x20) >> 5];
					pixel_pointer[0x3] = palette640[(bitmap[0] & 0x10) >> 4];
					pixel_pointer[0x4] = palette640[(bitmap[0] & 0x08) >> 3];
					pixel_pointer[0x5] = palette640[(bitmap[0] & 0x04) >> 2];
					pixel_pointer[0x6] = palette640[(bitmap[0] & 0x02) >> 1];
					pixel_pointer[0x7] = palette640[(bitmap[0] & 0x01) >> 0];
					pixel_pointer[0x8] = palette640[(bitmap[1] & 0x80) >> 7];
					pixel_pointer[0x9] = palette640[(bitmap[1] & 0x40) >> 6];
					pixel_pointer[0xa] = palette640[(bitmap[1] & 0x20) >> 5];
					pixel_pointer[0xb] = palette640[(bitmap[1] & 0x10) >> 4];
					pixel_pointer[0xc] = palette640[(bitmap[1] & 0x08) >> 3];
					pixel_pointer[0xd] = palette640[(bitmap[1] & 0x04) >> 2];
					pixel_pointer[0xe] = palette640[(bitmap[1] & 0x02) >> 1];
					pixel_pointer[0xf] = palette640[(bitmap[1] & 0x01) >> 0];
				}
			}

			void serialise_text(const Motorola::CRTC::BusState &state) {
				const uint8_t attributes = ram[((state.refresh_address << 1) + 1) & 0x3fff];
				const uint8_t glyph = ram[((state.refresh_address << 1) + 0) & 0x3fff];
				const uint8_t row = font[(glyph * 8) + state.row_address];

				uint8_t colours[2] = { rgb(attributes >> 4), rgbi(attributes) };

				// Apply blink or background intensity.
				if(control_ & 0x20) {
					// Set both colours to black if within a blink; otherwise consider a yellow-to-brown conversion.
					if((attributes & 0x80) && (state.field_count & 16)) {
						colours[0] = colours[1] = 0;
					} else {
						colours[0] = yellow_to_brown(colours[0]);
					}
				} else {
					if(attributes & 0x80) {
						colours[0] = bright(colours[0]);
					} else {
						// Yellow to brown definitely doesn't apply if the colour has been brightened.
						colours[0] = yellow_to_brown(colours[0]);
					}
				}

				// Draw according to ROM contents.
				pixel_pointer[0] = (row & 0x80) ? colours[1] : colours[0];
				pixel_pointer[1] = (row & 0x40) ? colours[1] : colours[0];
				pixel_pointer[2] = (row & 0x20) ? colours[1] : colours[0];
				pixel_pointer[3] = (row & 0x10) ? colours[1] : colours[0];
				pixel_pointer[4] = (row & 0x08) ? colours[1] : colours[0];
				pixel_pointer[5] = (row & 0x04) ? colours[1] : colours[0];
				pixel_pointer[6] = (row & 0x02) ? colours[1] : colours[0];
				pixel_pointer[7] = (row & 0x01) ? colours[1] : colours[0];
			}

			Outputs::CRT::CRT crt;
			static constexpr size_t DefaultAllocationSize = 320;

			// Current output stream.
			uint8_t *pixels = nullptr;
			uint8_t *pixel_pointer = nullptr;
			int active_pixels_per_tick = 8;
			int active_clock_divider = 1;
			uint8_t active_border_colour = 0;

			// Source data.
			const uint8_t *ram = nullptr;
			std::vector<uint8_t> font;

			// CRTC state tracking, for CRT serialisation.
			OutputState output_state = OutputState::Sync;
			int count = 0;

			bool previous_hsync = false;
			int cycles_since_hsync = 0;

			// Current Programmer-set parameters.
			int clock_divider = 1;
			int pixels_per_tick = 8;
			uint8_t colours_ = 0;
			uint8_t control_ = 0;
			bool is_composite_ = false;
			enum class Mode {
				Pixels640, Pixels320, Text,
			} mode_ = Mode::Text;

			uint8_t palette320[4]{};
			uint8_t palette640[2]{};
			uint8_t border_colour;

			void update_palette() {
				// b5: 320x200 palette, unless in monochrome mode.
				if(control_ & 0x04) {
					palette320[1] = DarkCyan;
					palette320[2] = DarkRed;
					palette320[3] = DarkGrey;
				} else {
					if(colours_ & 0x20) {
						palette320[1] = DarkCyan;
						palette320[2] = DarkMagenta;
						palette320[3] = DarkGrey;
					} else {
						palette320[1] = DarkGreen;
						palette320[2] = DarkRed;
						palette320[3] = DarkYellow;
					}
				}

				// b4: set 320x200 palette into high intensity.
				if(colours_ & 0x10) {
					palette320[1] = bright(palette320[1]);
					palette320[2] = bright(palette320[2]);
					palette320[3] = bright(palette320[3]);
				} else {
					// Remap dark yellow to brown if applicable.
					palette320[3] = yellow_to_brown(palette320[3]);
				}

				// b3–b0: set background, border, monochrome colour.
				palette640[1] = palette320[0] = rgbi(colours_);
				border_colour = (mode_ != Mode::Pixels640) ? palette320[0] : 0;
			}

			//
			// Named colours and mapping logic.
			//
			static constexpr uint8_t DarkCyan		= 0b00'10'10;
			static constexpr uint8_t DarkMagenta	= 0b10'00'10;
			static constexpr uint8_t DarkGrey		= 0b10'10'10;

			static constexpr uint8_t DarkGreen		= 0b00'10'00;
			static constexpr uint8_t DarkRed		= 0b10'00'00;
			static constexpr uint8_t DarkYellow		= 0b10'10'00;

			static constexpr uint8_t Brown			= 0b10'01'00;

			/// @returns @c Brown if @c source is @c DarkYellow and composite output is not enabled; @c source otherwise.
			constexpr uint8_t yellow_to_brown(uint8_t source) {
				return (source == DarkYellow && !is_composite_) ? Brown : source;
			}

			/// @returns The brightened (i.e. high intensity) version of @c source.
			constexpr uint8_t bright(uint8_t source) {
				return source | (source >> 1);
			}

			/// Maps the RGB TTL triplet @c source to an appropriate output colour.
			constexpr uint8_t rgb(uint8_t source) {
				return uint8_t(
					((source & 0x01) << 1) |
					((source & 0x02) << 2) |
					((source & 0x04) << 3)
				);
			}

			/// Maps the RGBI value in @c source to an appropriate output colour, including potential yellow-to-brown conversion.
			constexpr uint8_t rgbi(uint8_t source) {
				const uint8_t result = rgb(source);
				return (source & 0x10) ? bright(result) : yellow_to_brown(result);
			}
		} outputter_;
		Motorola::CRTC::CRTC6845<
			CRTCOutputter,
			Motorola::CRTC::Personality::HD6845S,
			Motorola::CRTC::CursorType::MDA> crtc_;

		int full_clock_ = 0;

};

}