CLK/Machines/Atari/ST/Video.hpp

//
//  Video.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 04/10/2019.
//  Copyright © 2019 Thomas Harte. All rights reserved.
//

#ifndef Atari_ST_Video_hpp
#define Atari_ST_Video_hpp

#include "../../../Outputs/CRT/CRT.hpp"
#include "../../../ClockReceiver/ClockReceiver.hpp"

#include <vector>

namespace Atari {
namespace ST {

/*!
	Models a combination of the parts of the GLUE, MMU and Shifter that in net
	form the video subsystem of the Atari ST. So not accurate to a real chip, but
	(hopefully) to a subsystem.
*/
class Video {
	public:
		Video();

		/*!
			Sets the memory pool that provides video, and its size.
		*/
		void set_ram(uint16_t *, size_t size);

		/*!
			Sets the target device for video data.
		*/
		void set_scan_target(Outputs::Display::ScanTarget *scan_target);

		/*!
			Produces the next @c duration period of pixels.
		*/
		void run_for(HalfCycles duration);


		/*!
			@returns the number of cycles until there is next a change in the hsync,
			vsync or display_enable outputs.
		*/
		HalfCycles get_next_sequence_point();

		/*!
			@returns @c true if the horizontal sync output is currently active; @c false otherwise.

			@discussion On an Atari ST, this generates a VPA-style interrupt, which is often erroneously
			documented as being triggered by horizontal blank.
		*/
		bool hsync();

		/*!
			@returns @c true if the vertical sync output is currently active; @c false otherwise.

			@discussion On an Atari ST, this generates a VPA-style interrupt, which is often erroneously
			documented as being triggered by vertical blank.
		*/
		bool vsync();

		/*!
			@returns @c true if the display enabled output is currently active; @c false otherwise.

			@discussion On an Atari ST this is fed to the MFP. The documentation that I've been able to
			find implies a total 28-cycle delay between the real delay enabled signal changing and its effect
			on the 68000 interrupt input via the MFP. As I have yet to determine how much delay is caused
			by the MFP a full 28-cycle delay is applied by this class. This should be dialled down when the
			MFP's responsibility is clarified.
		*/
		bool display_enabled();

		/// @returns the effect of reading from @c address; only the low 6 bits are decoded.
		uint16_t read(int address);

		/// Writes @c value to @c address, of which only the low 6 bits are decoded.
		void write(int address, uint16_t value);

		/// Used internally to track state.
		enum class FieldFrequency {
			Fifty = 0, Sixty = 1, SeventyTwo = 2
		};

	private:
		Outputs::CRT::CRT crt_;

		uint16_t raw_palette_[16];
		uint16_t palette_[16];
		int base_address_ = 0;
		int current_address_ = 0;

		uint16_t *ram_ = nullptr;
		uint16_t line_buffer_[256];

		int x_ = 0, y_ = 0, next_y_ = 0;

		uint16_t video_mode_ = 0;
		uint16_t sync_mode_ = 0;

		FieldFrequency field_frequency_ = FieldFrequency::Fifty;
		enum class OutputBpp {
			One, Two, Four
		} output_bpp_ = OutputBpp::Four;
		void update_output_mode();

		struct HorizontalState {
			bool enable = false;
			bool blank = false;
			bool sync = false;
		} horizontal_;
		struct VerticalState {
			bool enable = false;
			bool blank = false;

			enum class SyncSchedule {
				/// No sync events this line.
				None,
				/// Sync should begin during this horizontal line.
				Begin,
				/// Sync should end during this horizontal line.
				End,
			} sync_schedule = SyncSchedule::None;
			bool sync = false;
		} vertical_, next_vertical_;
		int line_length_ = 1024;

		int data_latch_position_ = 0;
		uint16_t data_latch_[4] = {0, 0, 0, 0};
		void latch_word();

		class Shifter {
			public:
				Shifter(Outputs::CRT::CRT &crt, uint16_t *palette) : crt_(crt), palette_(palette) {}
				void output_blank(int duration);
				void output_sync(int duration);
				void output_border(int duration, OutputBpp bpp);
				void output_pixels(int duration, OutputBpp bpp);

				void load(uint64_t value);

			private:
				int duration_ = 0;
				enum class OutputMode {
					Sync, Blank, Border, Pixels
				} output_mode_ = OutputMode::Sync;
				uint16_t border_colour_ = 0;
				OutputBpp bpp_ = OutputBpp::Four;
				union {
					uint64_t output_shifter_;
					uint32_t shifter_halves_[2];
				};

				void flush_output(OutputMode next_mode);

				uint16_t *pixel_buffer_ = nullptr;
				size_t pixel_pointer_ = 0;

				Outputs::CRT::CRT &crt_;
				uint16_t *palette_ = nullptr;
		} shifter_;

		/// Contains copies of the various observeable fields, after the relevant propagation delay.
		struct PublicState {
			bool display_enable = false;
		} public_state_;

		struct Event {
			int delay;
			enum class Type {
				SetDisplayEnable, ResetDisplayEnable
			} type;

			Event(Type type, int delay) : delay(delay), type(type) {}

			void apply(PublicState &state) {
				apply(type, state);
			}

			static void apply(Type type, PublicState &state) {
				switch(type) {
					default:
					case Type::SetDisplayEnable:	state.display_enable = true;	break;
					case Type::ResetDisplayEnable:	state.display_enable = false;	break;
				}
			}
		};

		std::vector<Event> pending_events_;
		void add_event(int delay, Event::Type type) {
			// Apply immediately if there's no delay (or a negative delay).
			if(delay <= 0) {
				Event::apply(type, public_state_);
				return;
			}

			// Otherwise enqueue, having subtracted the delay for any preceding events,
			// and subtracting from the subsequent, if any.
			auto insertion_point = pending_events_.begin();
			while(insertion_point != pending_events_.end() && insertion_point->delay > delay) {
				delay -= insertion_point->delay;
				++insertion_point;
			}
			if(insertion_point != pending_events_.end()) {
				insertion_point->delay -= delay;
			}
			pending_events_.emplace(insertion_point, type, delay);
		}
};

}
}

#endif /* Atari_ST_Video_hpp */