CLK/Machines/AppleII/Video.hpp

//
//  Video.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 14/04/2018.
//  Copyright 2018 Thomas Harte. All rights reserved.
//

#ifndef Video_hpp
#define Video_hpp

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

#include <vector>

namespace AppleII {
namespace Video {

class BusHandler {
	public:
		uint8_t perform_read(uint16_t address) {
			return 0xff;
		}
};

class VideoBase {
	public:
		VideoBase();

		/// @returns The CRT this video feed is feeding.
		Outputs::CRT::CRT *get_crt();

		// Inputs for the various soft switches.
		void set_graphics_mode();
		void set_text_mode();
		void set_mixed_mode(bool);
		void set_video_page(int);
		void set_low_resolution();
		void set_high_resolution();

		// Setup for text mode.
		void set_character_rom(const std::vector<uint8_t> &);

	protected:
		std::unique_ptr<Outputs::CRT::CRT> crt_;

		uint8_t *pixel_pointer_ = nullptr;
		int pixel_pointer_column_ = 0;
		bool pixels_are_high_density_ = false;

		int video_page_ = 0;
		int row_ = 0, column_ = 0, flash_ = 0;
		std::vector<uint8_t> character_rom_;

		enum class GraphicsMode {
			LowRes,
			HighRes,
			Text
		} graphics_mode_ = GraphicsMode::LowRes;
		bool use_graphics_mode_ = false;
		bool mixed_mode_ = false;
		uint8_t graphics_carry_ = 0;
};

template <class BusHandler> class Video: public VideoBase {
	public:
		/// Constructs an instance of the video feed; a CRT is also created.
		Video(BusHandler &bus_handler) :
			VideoBase(),
			bus_handler_(bus_handler) {}

		/*!
			Advances time by @c cycles; expects to be fed by the CPU clock.
			Implicitly adds an extra half a colour clock at the end of every
			line.
		*/
		void run_for(const Cycles cycles) {
			/*
				Addressing scheme used throughout is that column 0 is the first column with pixels in it;
				row 0 is the first row with pixels in it.

				A frame is oriented around 65 cycles across, 262 lines down.
			*/
			static const int first_sync_line = 220;		// A complete guess. Information needed.
			static const int first_sync_column = 49;	// Also a guess.
			static const int sync_length = 4;			// One of the two likely candidates.

			int int_cycles = cycles.as_int();
			while(int_cycles) {
				const int cycles_this_line = std::min(65 - column_, int_cycles);
				const int ending_column = column_ + cycles_this_line;

				if(row_ >= first_sync_line && row_ < first_sync_line + 3) {
					// In effect apply an XOR to HSYNC and VSYNC flags in order to include equalising
					// pulses (and hencce keep hsync approximately where it should be during vsync).
					const int blank_start = std::max(first_sync_column - sync_length, column_);
					const int blank_end = std::min(first_sync_column, ending_column);
					if(blank_end > blank_start) {
						if(blank_start > column_) {
							crt_->output_sync(static_cast<unsigned int>(blank_start - column_) * 14);
						}
						crt_->output_blank(static_cast<unsigned int>(blank_end - blank_start) * 14);
						if(blank_end < ending_column) {
							crt_->output_sync(static_cast<unsigned int>(ending_column - blank_end) * 14);
						}
					} else {
						crt_->output_sync(static_cast<unsigned int>(cycles_this_line) * 14);
					}
				} else {
					const GraphicsMode line_mode = use_graphics_mode_ ? graphics_mode_ : GraphicsMode::Text;

					// The first 40 columns are submitted to the CRT only upon completion;
					// they'll be either graphics or blank, depending on which side we are
					// of line 192.
					if(column_ < 40) {
						if(row_ < 192) {
							GraphicsMode pixel_mode = (!mixed_mode_ || row_ < 160) ? line_mode : GraphicsMode::Text;
							bool requires_high_density = pixel_mode != GraphicsMode::Text;
							if(!column_ || requires_high_density != pixels_are_high_density_) {
								if(column_) output_data_to_column(column_);
								pixel_pointer_ = crt_->allocate_write_area(561);
								pixel_pointer_column_ = column_;
								pixels_are_high_density_ = requires_high_density;
								graphics_carry_ = 0;
							}

							const int pixel_end = std::min(40, ending_column);
							const int character_row = row_ >> 3;
							const int pixel_row = row_ & 7;
							const uint16_t row_address = static_cast<uint16_t>((character_row >> 3) * 40 + ((character_row&7) << 7));
							const uint16_t text_address = static_cast<uint16_t>(((video_page_+1) * 0x400) + row_address);

							switch(pixel_mode) {
								case GraphicsMode::Text: {
									const uint8_t inverses[] = {
										0xff,
										static_cast<uint8_t>((flash_ / flash_length) * 0xff),
										0x00,
										0x00
									};
									for(int c = column_; c < pixel_end; ++c) {
										const uint8_t character = bus_handler_.perform_read(static_cast<uint16_t>(text_address + c));
										const std::size_t character_address = static_cast<std::size_t>(((character & 0x3f) << 3) + pixel_row);

										const uint8_t character_pattern = character_rom_[character_address] ^ inverses[character >> 6];

										// The character ROM is output MSB to LSB rather than LSB to MSB.
										pixel_pointer_[0] = character_pattern & 0x40;
										pixel_pointer_[1] = character_pattern & 0x20;
										pixel_pointer_[2] = character_pattern & 0x10;
										pixel_pointer_[3] = character_pattern & 0x08;
										pixel_pointer_[4] = character_pattern & 0x04;
										pixel_pointer_[5] = character_pattern & 0x02;
										pixel_pointer_[6] = character_pattern & 0x01;
										graphics_carry_ = character_pattern & 0x40;
										pixel_pointer_ += 7;
									}
								} break;

								case GraphicsMode::LowRes: {
									const int row_shift = (row_&4);
									// TODO: decompose into two loops, possibly.
									for(int c = column_; c < pixel_end; ++c) {
										const uint8_t nibble = (bus_handler_.perform_read(static_cast<uint16_t>(text_address + c)) >> row_shift) & 0x0f;

										// Low-resolution graphics mode shifts the colour code on a loop, but has to account for whether this
										// 14-sample output window is starting at the beginning of a colour cycle or halfway through.
										if(c&1) {
											pixel_pointer_[0] = pixel_pointer_[4] = pixel_pointer_[8] = pixel_pointer_[12] = nibble & 4;
											pixel_pointer_[1] = pixel_pointer_[5] = pixel_pointer_[9] = pixel_pointer_[13] = nibble & 8;
											pixel_pointer_[2] = pixel_pointer_[6] = pixel_pointer_[10] = nibble & 1;
											pixel_pointer_[3] = pixel_pointer_[7] = pixel_pointer_[11] = nibble & 2;
											graphics_carry_ = nibble & 8;
										} else {
											pixel_pointer_[0] = pixel_pointer_[4] = pixel_pointer_[8] = pixel_pointer_[12] = nibble & 1;
											pixel_pointer_[1] = pixel_pointer_[5] = pixel_pointer_[9] = pixel_pointer_[13] = nibble & 2;
											pixel_pointer_[2] = pixel_pointer_[6] = pixel_pointer_[10] = nibble & 4;
											pixel_pointer_[3] = pixel_pointer_[7] = pixel_pointer_[11] = nibble & 8;
											graphics_carry_ = nibble & 2;
										}
										pixel_pointer_ += 14;
									}
								} break;

								case GraphicsMode::HighRes: {
									const uint16_t graphics_address = static_cast<uint16_t>(((video_page_+1) * 0x2000) + row_address + ((pixel_row&7) << 10));
									for(int c = column_; c < pixel_end; ++c) {
										const uint8_t graphic = bus_handler_.perform_read(static_cast<uint16_t>(graphics_address + c));

										// High resolution graphics shift out LSB to MSB, optionally with a delay of half a pixel.
										// If there is a delay, the previous output level is held to bridge the gap.
										if(graphic & 0x80) {
											pixel_pointer_[0] = graphics_carry_;
											pixel_pointer_[1] = pixel_pointer_[2] = graphic & 0x01;
											pixel_pointer_[3] = pixel_pointer_[4] = graphic & 0x02;
											pixel_pointer_[5] = pixel_pointer_[6] = graphic & 0x04;
											pixel_pointer_[7] = pixel_pointer_[8] = graphic & 0x08;
											pixel_pointer_[9] = pixel_pointer_[10] = graphic & 0x10;
											pixel_pointer_[11] = pixel_pointer_[12] = graphic & 0x20;
											pixel_pointer_[13] = graphic & 0x40;
										} else {
											pixel_pointer_[0] = pixel_pointer_[1] = graphic & 0x01;
											pixel_pointer_[2] = pixel_pointer_[3] = graphic & 0x02;
											pixel_pointer_[4] = pixel_pointer_[5] = graphic & 0x04;
											pixel_pointer_[6] = pixel_pointer_[7] = graphic & 0x08;
											pixel_pointer_[8] = pixel_pointer_[9] = graphic & 0x10;
											pixel_pointer_[10] = pixel_pointer_[11] = graphic & 0x20;
											pixel_pointer_[12] = pixel_pointer_[13] = graphic & 0x40;
										}
										graphics_carry_ = graphic & 0x40;
										pixel_pointer_ += 14;
									}
								} break;
							}

							if(ending_column >= 40) {
								output_data_to_column(40);
							}
						} else {
							if(ending_column >= 40) {
								crt_->output_blank(560);
							}
						}
					}

					/*
						The left border, sync, right border pattern doesn't depend on whether
						there were pixels this row and is output as soon as it is known.
					*/

					const int first_blank_start = std::max(40, column_);
					const int first_blank_end = std::min(first_sync_column, ending_column);
					if(first_blank_end > first_blank_start) {
						crt_->output_blank(static_cast<unsigned int>(first_blank_end - first_blank_start) * 14);
					}

					const int sync_start = std::max(first_sync_column, column_);
					const int sync_end = std::min(first_sync_column + sync_length, ending_column);
					if(sync_end > sync_start) {
						crt_->output_sync(static_cast<unsigned int>(sync_end - sync_start) * 14);
					}

					int second_blank_start;
					if(line_mode != GraphicsMode::Text && (!mixed_mode_ || row_ < 159 || row_ >= 192)) {
						const int colour_burst_start = std::max(first_sync_column + sync_length + 1, column_);
						const int colour_burst_end = std::min(first_sync_column + sync_length + 4, ending_column);
						if(colour_burst_end > colour_burst_start) {
							crt_->output_default_colour_burst(static_cast<unsigned int>(colour_burst_end - colour_burst_start) * 14);
						}

						second_blank_start = std::max(first_sync_column + 7, column_);
					} else {
						second_blank_start = std::max(first_sync_column + 4, column_);
					}

					if(ending_column > second_blank_start) {
						crt_->output_blank(static_cast<unsigned int>(ending_column - second_blank_start) * 14);
					}
				}

				int_cycles -= cycles_this_line;
				column_ = (column_ + cycles_this_line) % 65;
				if(!column_) {
					row_ = (row_ + 1) % 262;
					flash_ = (flash_ + 1) % (2 * flash_length);

					// Add an extra half a colour cycle of blank; this isn't counted in the run_for
					// count explicitly but is promised.
					crt_->output_blank(2);
				}
			}
		}

		/*!
			Obtains the last value the video read prior to time now+offset.
		*/
		uint8_t get_last_read_value(Cycles offset) {
			// Rules of generation:
			// (1)	a complete sixty-five-cycle scan line consists of sixty-five consecutive bytes of
			//		display buffer memory that starts twenty-five bytes prior to the actual data to be displayed.
			// (2)	During VBL the data acts just as if it were starting a whole new frame from the beginning, but
			//		it never finishes this pseudo-frame. After getting one third of the way through the frame (to
			//		scan line $3F), it suddenly repeats the previous six scan lines ($3A through $3F) before aborting
			//		to begin the next true frame.
			//
			// Source: Have an Apple Split by Bob Bishop; http://rich12345.tripod.com/aiivideo/softalk.html

			// Determine column at offset.
			int mapped_column = column_ + offset.as_int();

			// Map that backwards from the internal pixels-at-start generation to pixels-at-end
			// (so what was column 0 is now column 25).
			mapped_column += 25;

			// Apply carry into the row counter.
			int mapped_row = row_ + (mapped_column / 65);
			mapped_column %= 65;
			mapped_row %= 262;

			// Apple out-of-bounds row logic.
			if(mapped_row >= 256) {
				mapped_row = 0x3a + (mapped_row&255);
			} else {
				mapped_row %= 192;
			}

			// Calculate the address and return the value.
			uint16_t read_address = static_cast<uint16_t>(get_row_address(mapped_row) + mapped_column - 25);
			return bus_handler_.perform_read(read_address);
		}

	private:
		uint16_t get_row_address(int row) {
			const int character_row = row >> 3;
			const int pixel_row = row & 7;
			const uint16_t row_address = static_cast<uint16_t>((character_row >> 3) * 40 + ((character_row&7) << 7));

			GraphicsMode pixel_mode = ((!mixed_mode_ || row < 160) && use_graphics_mode_) ? graphics_mode_ : GraphicsMode::Text;
			return (pixel_mode == GraphicsMode::HighRes) ?
				static_cast<uint16_t>(((video_page_+1) * 0x2000) + row_address + ((pixel_row&7) << 10)) :
				static_cast<uint16_t>(((video_page_+1) * 0x400) + row_address);
		}

		static const int flash_length = 8406;
		BusHandler &bus_handler_;
		void output_data_to_column(int column) {
			int length = column - pixel_pointer_column_;
			crt_->output_data(static_cast<unsigned int>(length*14), static_cast<unsigned int>(length * (pixels_are_high_density_ ? 14 : 7)));
			pixel_pointer_ = nullptr;
		}
};

}
}

#endif /* Video_hpp */