CLK/Machines/Apple/AppleIIgs/Video.hpp

//
//  Video.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 31/10/2020.
//  Copyright © 2020 Thomas Harte. All rights reserved.
//

#ifndef Apple_IIgs_Video_hpp
#define Apple_IIgs_Video_hpp

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

namespace Apple {
namespace IIgs {
namespace Video {

// This is coupled to Apple::II::GraphicsMode, but adds detail for the IIgs.
enum class GraphicsMode {
	Text = 0,
	DoubleText,
	HighRes,
	DoubleHighRes,
	LowRes,
	DoubleLowRes,
	FatLowRes,

	// Additions:
	DoubleHighResMono,
	SuperHighRes
};
constexpr bool is_colour_ntsc(GraphicsMode m) { return m >= GraphicsMode::HighRes && m <= GraphicsMode::FatLowRes; }

enum class PixelBufferFormat {
	Text, DoubleText, NTSC, NTSCMono, SuperHighRes
};
constexpr PixelBufferFormat format_for_mode(GraphicsMode m) {
	switch(m) {
		case GraphicsMode::Text:				return PixelBufferFormat::Text;
		case GraphicsMode::DoubleText:			return PixelBufferFormat::DoubleText;
		default: 								return PixelBufferFormat::NTSC;
		case GraphicsMode::DoubleHighResMono:	return PixelBufferFormat::NTSCMono;
		case GraphicsMode::SuperHighRes:		return PixelBufferFormat::SuperHighRes;
	}
}

/*!
	Provides IIgs video output; assumed clocking here is twice the usual Apple II clock.
	So it'll produce a single line of video every 131 cycles — 65*2 + 1, allowing for the
	stretched cycle.
*/
class VideoBase: public Apple::II::VideoSwitches<Cycles> {
	public:
		VideoBase();
		void set_internal_ram(const uint8_t *);

		bool get_is_vertical_blank(Cycles offset);

		void set_new_video(uint8_t);
		uint8_t get_new_video();

		void clear_interrupts(uint8_t);
		uint8_t get_interrupt_register();
		void set_interrupt_register(uint8_t);

		void notify_clock_tick();

		void set_border_colour(uint8_t);
		void set_text_colour(uint8_t);

		void set_composite_is_colour(bool);
		bool get_composite_is_colour();

		/// Sets the scan target.
		void set_scan_target(Outputs::Display::ScanTarget *scan_target);

		/// Gets the current scan status.
		Outputs::Display::ScanStatus get_scaled_scan_status() const;

		/// Sets the type of output.
		void set_display_type(Outputs::Display::DisplayType);

		/// Gets the type of output.
		Outputs::Display::DisplayType get_display_type() const;

		/// Determines the period until video might autonomously update its interrupt lines.
		Cycles get_next_sequence_point() const;

	private:
		Outputs::CRT::CRT crt_;

		GraphicsMode graphics_mode(int row) const {
			if(new_video_ & 0x80) {
				return GraphicsMode::SuperHighRes;
			}

			const auto ii_mode = Apple::II::VideoSwitches<Cycles>::graphics_mode(row);
			switch(ii_mode) {
				// Coupling very much assumed here.
				case Apple::II::GraphicsMode::DoubleHighRes:
					if(new_video_ & 0x20) {
						return GraphicsMode::DoubleHighResMono;
					}
				[[fallthrough]];

				default: return GraphicsMode(int(ii_mode));	break;
			}
		}

		void advance(Cycles);

		uint8_t new_video_ = 0x01;
		uint8_t interrupts_ = 0x00;
		void set_interrupts(uint8_t);

		int cycles_into_frame_ = 0;
		const uint8_t *ram_ = nullptr;

		// The modal colours.
		uint16_t border_colour_ = 0;
		uint16_t text_colour_ = 0xffff;
		uint16_t background_colour_ = 0;

		// Current pixel output buffer and conceptual format.
		PixelBufferFormat pixels_format_;
		uint16_t *pixels_ = nullptr, *next_pixel_ = nullptr;
		int pixels_start_column_;

		void output_row(int row, int start, int end);

		uint16_t *output_super_high_res(uint16_t *target, int start, int end, int row) const;

		uint16_t *output_text(uint16_t *target, int start, int end, int row) const;
		uint16_t *output_double_text(uint16_t *target, int start, int end, int row) const;
		uint16_t *output_char(uint16_t *target, uint8_t source, int row) const;

		uint16_t *output_low_resolution(uint16_t *target, int start, int end, int row);
		uint16_t *output_fat_low_resolution(uint16_t *target, int start, int end, int row);
		uint16_t *output_double_low_resolution(uint16_t *target, int start, int end, int row);

		uint16_t *output_high_resolution(uint16_t *target, int start, int end, int row);
		uint16_t *output_double_high_resolution(uint16_t *target, int start, int end, int row);
		uint16_t *output_double_high_resolution_mono(uint16_t *target, int start, int end, int row);

		// Super high-res per-line state.
		uint8_t line_control_;
		uint16_t palette_[16];

		// Storage used for fill mode.
		uint16_t *palette_zero_[4] = {nullptr, nullptr, nullptr, nullptr}, palette_throwaway_;

		// Lookup tables and state to assist in the IIgs' mapping from NTSC to RGB.
		//
		// My understanding of the real-life algorithm is: maintain a four-bit buffer.
		// Fill it in a circular fashion. Ordinarily, output the result of looking
		// up the RGB mapping of those four bits of Apple II output (which outputs four
		// bits per NTSC colour cycle), commuted as per current phase. But if the bit
		// being inserted differs from that currently in its position in the shift
		// register, hold the existing output for three shifts.
		//
		// From there I am using the following:

		// Maps from:
		//
		//	b0 = b0 of the shift register
		//	b1 = b4 of the shift register
		//	b2– = current delay count
		//
		// to a new delay count.
		uint8_t ntsc_delay_lookup_[20];
		uint32_t ntsc_shift_ = 0;	// Assumption here: logical shifts will ensue, rather than arithmetic.
		int ntsc_delay_ = 0;

		/// Outputs the lowest 14 bits from @c ntsc_shift_, mapping to RGB.
		/// Phase is derived from @c column.
		uint16_t *output_shift(uint16_t *target, int column);
};

class Video: public VideoBase {
	public:
		using VideoBase::VideoBase;
};

}
}
}

#endif /* Video_hpp */