CLK/Machines/Enterprise/Nick.cpp

//
//  Nick.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 14/06/2021.
//  Copyright © 2021 Thomas Harte. All rights reserved.
//

#include "Nick.hpp"

#include <cstdio>

namespace  {

uint16_t mapped_colour(uint8_t source) {
	// On the Enterprise, red and green are 3-bit quantities; blue is a 2-bit quantity.
	const int red	= ((source&0x01) << 2) | ((source&0x08) >> 2) | ((source&0x40) >> 6);
	const int green	= ((source&0x02) << 1) | ((source&0x10) >> 3) | ((source&0x80) >> 7);
	const int blue	= ((source&0x04) >> 1) | ((source&0x20) >> 5);

	// Duplicate bits where necessary to map to a full 4-bit range per channel.
	const uint8_t parts[2] = {
		uint8_t(
			(red << 1) + ((red&0x4) >> 3)
		),
		uint8_t(
			(green << 5) + ((green&0x4) << 2) +
			(blue << 2) + blue
		)
	};
	return *reinterpret_cast<const uint16_t *>(parts);
}

}

using namespace Enterprise;

Nick::Nick(const uint8_t *ram) :
	crt_(57*16, 16, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red4Green4Blue4),
	ram_(ram) {

	// Just use RGB for now.
	crt_.set_display_type(Outputs::Display::DisplayType::RGB);
}

void Nick::write(uint16_t address, uint8_t value) {
	switch(address & 3) {
		case 0:
			// Ignored: everything to do with external colour.
			for(int c = 0; c < 8; c++) {
				palette_[c + 8] = mapped_colour(uint8_t(((value & 0x1f) << 3) + c));
			}
		break;
		case 1:
			flush_border();
			border_colour_ = mapped_colour(value);
		break;
		case 2:
			line_parameter_base_ = uint16_t((line_parameter_base_ & 0xf000) | (value << 4));
		break;
		case 3:
			line_parameter_base_ = uint16_t((line_parameter_base_ & 0x0ff0) | (value << 12));

			// Still a mystery to me: the exact meaning of the top two bits here. For now
			// just treat a 0 -> 1 transition of the MSB as a forced frame restart.
			if((value^line_parameter_control_) & value & 0x80) {
				// For now: just force this to be the final line of this mode block.
				// I'm unclear whether I should also reset the horizontal counter
				// (i.e. completely abandon current video phase).
				lines_remaining_ = 0xff;
				line_parameters_[1] |= 1;
			}
			line_parameter_control_ = value & 0xc0;
		break;
	}
}

uint8_t Nick::read([[maybe_unused]] uint16_t address) {
	return 0xff;
}

void Nick::run_for(Cycles duration) {
	constexpr int line_length = 912;

	int clocks_remaining = duration.as<int>();
	while(clocks_remaining) {
		// Determine how many cycles are left this line.
		const int clocks_this_line = std::min(clocks_remaining, line_length - horizontal_counter_);

		// Convert that into a [start/current] and end window.
		int window = horizontal_counter_ >> 4;
		const int end_window = (horizontal_counter_ + clocks_this_line) >> 4;

		// Advance the line counters.
		clocks_remaining -= clocks_this_line;
		horizontal_counter_ = (horizontal_counter_ + clocks_this_line) % line_length;

		// Do nothing if a window boundary isn't crossed.
		if(window == end_window) continue;

		// If this is within the first 8 cycles of the line, [possibly] fetch
		// the relevant part of the line parameters.
		if(should_reload_line_parameters_ && window < 8) {
			int fetch_spot = window;
			while(fetch_spot < end_window && fetch_spot < 8) {
				line_parameters_[(fetch_spot << 1)] = ram_[line_parameter_pointer_];
				line_parameters_[(fetch_spot << 1) + 1] = ram_[line_parameter_pointer_ + 1];
				line_parameter_pointer_ += 2;
				++fetch_spot;
			}

			// TODO: when exactly does the interrupt output change? Am I a window too late? Or two too early?

			// Special: set mode as soon as it's known. It'll be needed at the end of HSYNC.
			if(window < 2 && fetch_spot >= 2) {
				// Set length of mode line.
				lines_remaining_ = line_parameters_[0];

				// Set the new interrupt line output.
				interrupt_line_ = line_parameters_[1] & 0x80;

				// Determine the margins.
				left_margin_ = line_parameters_[2] & 0x3f;
				right_margin_ = line_parameters_[3] & 0x3f;

				// Determine the mode and depth, and hence the column size.
				mode_ = Mode((line_parameters_[1] >> 1)&7);
				bpp_ = 1 << ((line_parameters_[1] >> 5)&3);
				switch(mode_) {
					default:
					case Mode::Pixel:	column_size_ = 16 / bpp_;	break;
					case Mode::CH64:
					case Mode::CH128:
					case Mode::CH256:
					case Mode::LPixel:	column_size_ = 8 / bpp_;	break;
					case Mode::Attr:	column_size_ = 8;			break;
				}

				// Act as if proper state transitions had occurred while HSYNC is being output.
				if(mode_ == Mode::Vsync) {
					state_ = State::Blank;
				} else {
					// The first ten windows are occupied by the horizontal sync and
					// colour burst; if left signalled before then, begin in pixels.
					state_ = left_margin_ > 10 ? State::Border : State::Pixels;
				}
			}

			// If all parameters have been loaded, set appropriate fields.
			if(fetch_spot == 8) {
				should_reload_line_parameters_ = false;

				// Determine the line data pointers.
				line_data_pointer_[0] = uint16_t(line_parameters_[4] | (line_parameters_[5] << 8));
				line_data_pointer_[1] = uint16_t(line_parameters_[6] | (line_parameters_[7] << 8));

				// Populate the first eight colours of the palette.
				for(int c = 0; c < 8; c++) {
					palette_[c] = mapped_colour(line_parameters_[8 + c]);
				}

				switch(mode_) {
					default:
					break;

					// NB: LSBALT/MSBALT and ALTIND0/ALTIND1 appear to have opposite effects on palette selection.

					case Mode::Pixel:
					case Mode::LPixel:
						// Use MSBALT and LSBALT to pick the alt_ind_palettes.
						//
						// LSBALT = b6 of params[2], if set => character codes with bit 6 set should use palette indices 4... instead of 0... .
						// MSBALT = b7 of params[2], if set => character codes with bit 7 set should use palette indices 2 and 3.
						two_colour_mask_ = 0xff &~ (((line_parameters_[2]&0x80) >> 7) | ((line_parameters_[2]&0x40) << 1));

						alt_ind_palettes[0] = palette_;
						alt_ind_palettes[2] = alt_ind_palettes[0] + ((line_parameters_[2] & 0x80) ? 2 : 0);

						alt_ind_palettes[1] = alt_ind_palettes[0] + ((line_parameters_[2] & 0x40) ? 4 : 0);
						alt_ind_palettes[3] = alt_ind_palettes[2] + ((line_parameters_[2] & 0x40) ? 4 : 0);
					break;

					case Mode::CH64:
					case Mode::CH128:
					case Mode::CH256:
						// Use ALTIND0 and ALTIND1 to pick the alt_ind_palettes.
						//
						// ALTIND1 = b6 of params[3], if set => character codes with bit 7 set should use palette indices 2 and 3.
						// ALTIND0 = b7 of params[3], if set => character codes with bit 6 set should use palette indices 4... instead of 0... .
						alt_ind_palettes[0] = palette_;
						alt_ind_palettes[2] = alt_ind_palettes[0] + ((line_parameters_[3] & 0x40) ? 2 : 0);

						alt_ind_palettes[1] = alt_ind_palettes[0] + ((line_parameters_[3] & 0x80) ? 4 : 0);
						alt_ind_palettes[3] = alt_ind_palettes[2] + ((line_parameters_[3] & 0x80) ? 4 : 0);
					break;
				}
			}
		}

		// HSYNC is signalled for four windows at the start of the line.
		// I currently belive this happens regardless of Vsync mode.
		if(window < 4 && end_window >= 4) {
			crt_.output_sync(4*16);
			window = 4;
		}

		// Deal with vsync mode out here.
		if(mode_ == Mode::Vsync) {
			if(window >= 4) {
				while(window < end_window) {
					int next_event = end_window;
					if(window < left_margin_) next_event = std::min(next_event, left_margin_);
					if(window < right_margin_) next_event = std::min(next_event, right_margin_);

					if(state_ == State::Blank) {
						crt_.output_blank((next_event - window)*16);
					} else {
						crt_.output_sync((next_event - window)*16);
					}

					window = next_event;
					if(window == left_margin_) state_ = State::Sync;
					if(window == right_margin_) state_ = State::Blank;
				}
			}
		} else {
			// If present then the colour burst is output for the period from
			// the start of window 6 to the end of window 10.
			if(window < 10 && end_window >= 10) {
				crt_.output_blank(2*16);
				crt_.output_colour_burst(4*16, 0);	// TODO: try to determine actual phase.
				window = 10;
			}

			if(window >= 10) {
				while(window < end_window) {
					int next_event = end_window;
					if(window < left_margin_) next_event = std::min(next_event, left_margin_);
					if(window < right_margin_) next_event = std::min(next_event, right_margin_);

					if(state_ == State::Border) {
						border_duration_ += next_event - window;
					} else {
#define DispatchBpp(func) \
	switch(bpp_) {	\
		default:	\
		case 1: func(1)(pixel_pointer_, output_duration);	break;	\
		case 2: func(2)(pixel_pointer_, output_duration);	break;	\
		case 4: func(4)(pixel_pointer_, output_duration);	break;	\
		case 8: func(8)(pixel_pointer_, output_duration);	break;	\
	}

#define pixel(x) output_pixel<x, false>
#define lpixel(x) output_pixel<x, true>
#define ch256(x) output_character<x, 8>
#define ch128(x) output_character<x, 7>
#define ch64(x) output_character<x, 6>
#define attr(x) output_attributed<x>

						int columns_remaining = next_event - window;
						while(columns_remaining) {
							if(!allocated_pointer_) {
								flush_pixels();
								pixel_pointer_ = allocated_pointer_ = reinterpret_cast<uint16_t *>(crt_.begin_data(allocation_size));
							}

							if(allocated_pointer_) {
								const int output_duration = std::min(columns_remaining, int(allocated_pointer_ + allocation_size - pixel_pointer_) / column_size_);

								switch(mode_) {
									default:
									case Mode::Pixel:	DispatchBpp(pixel);		break;
									case Mode::LPixel:	DispatchBpp(lpixel);	break;
									case Mode::CH256:	DispatchBpp(ch256);		break;
									case Mode::CH128:	DispatchBpp(ch128);		break;
									case Mode::CH64:	DispatchBpp(ch64);		break;
									case Mode::Attr:	DispatchBpp(attr);		break;
								}

								pixel_pointer_ += output_duration * column_size_;
								pixel_duration_ += output_duration;
								if(pixel_pointer_ - allocated_pointer_ == allocation_size) {
									flush_pixels();
								}
								columns_remaining -= output_duration;
							} else {
								// TODO: advance line pointers.

								// Advance pixel pointer, so as to be able to supply something
								// convincing to the CRT as to the number of samples that would have
								// been provided, and skip asking for further allocations for now.
								pixel_pointer_ += columns_remaining * column_size_;
								pixel_duration_ += columns_remaining;
								columns_remaining = 0;
							}
						}
#undef attr
#undef ch64
#undef ch128
#undef ch256
#undef pixel
#undef lpixel
#undef DispatchBpp
					}

					window = next_event;
					if(window == left_margin_) {
						flush_border();
						state_ = State::Pixels;
					}
					if(window == right_margin_) {
						flush_pixels();
						state_ = State::Border;
					}
				}
			}

			// Finish up the line.
			if(!horizontal_counter_) {
				if(state_ == State::Border) {
					flush_border();
				} else {
					flush_pixels();
				}
			}
		}

		// Check for end of line.
		if(!horizontal_counter_) {
			++lines_remaining_;
			if(!lines_remaining_) {
				should_reload_line_parameters_ = true;

				// Check for end-of-frame.
				if(line_parameters_[1] & 1) {
					line_parameter_pointer_ = line_parameter_base_;
				}
			}

			// Deal with VRES and other address reloading, dependant upon mode.
			switch(mode_) {
				default: break;
				case Mode::CH64:
				case Mode::CH128:
				case Mode::CH256:
					line_data_pointer_[0] = uint16_t(line_parameters_[4] | (line_parameters_[5] << 8));
					++line_data_pointer_[1];
				break;

				case Mode::Attr:
					// Reload the attribute address if VRES is set.
					if(line_parameters_[1] & 0x10) {
						line_data_pointer_[0] = uint16_t(line_parameters_[4] | (line_parameters_[5] << 8));
					}
				break;

				case Mode::Pixel:
				case Mode::LPixel:
					// If VRES is clear, reload the pixel address.
					if(!(line_parameters_[1] & 0x10)) {
						line_data_pointer_[0] = uint16_t(line_parameters_[4] | (line_parameters_[5] << 8));
					}
				break;
			}
		}
	}
}

void Nick::flush_border() {
	if(!border_duration_) return;

	uint16_t *const colour_pointer = reinterpret_cast<uint16_t *>(crt_.begin_data(1));
	if(colour_pointer) *colour_pointer = border_colour_;
	crt_.output_level(border_duration_*16);
	border_duration_ = 0;
}

void Nick::flush_pixels() {
	if(!pixel_duration_) return;
	crt_.output_data(pixel_duration_*16, size_t(pixel_pointer_ - allocated_pointer_));
	pixel_duration_ = 0;
	pixel_pointer_ = nullptr;
	allocated_pointer_ = nullptr;
}

// MARK: - Sequence points.

Cycles Nick::get_next_sequence_point() {
	// TODO: the below is incorrect; unit test and correct.
	// Changing to e.g. Cycles(1) reveals the relevant discrepancy.
//	return Cycles(1);

	constexpr int load_point = 2*16;

	// Any mode line may cause a change in the interrupt output, so as a first blush
	// just always report the time until the end of the mode line.
	if(lines_remaining_ || horizontal_counter_ >= load_point) {
		return Cycles(load_point + (912 - horizontal_counter_) + (0xff - lines_remaining_) * 912);
	} else {
		return Cycles(load_point - horizontal_counter_);
	}
}

// MARK: - CRT passthroughs.

void Nick::set_scan_target(Outputs::Display::ScanTarget *scan_target) {
	crt_.set_scan_target(scan_target);
}

Outputs::Display::ScanStatus Nick::get_scaled_scan_status() const {
	return crt_.get_scaled_scan_status();
}

// MARK: - Specific pixel outputters.

template <int bpp, bool is_lpixel> void Nick::output_pixel(uint16_t *target, int columns) {
	static_assert(bpp == 1 || bpp == 2 || bpp == 4 || bpp == 8);

	for(int c = 0; c < columns; c++) {
		uint8_t pixels[2] = { ram_[line_data_pointer_[0]], ram_[(line_data_pointer_[0]+1) & 0xffff] };
		line_data_pointer_[0] += is_lpixel ? 1 : 2;

		switch(bpp) {
			default:
			case 1: {
				const uint16_t *palette = alt_ind_palettes[((pixels[0] >> 6) & 0x02) | (pixels[0]&1)];
				pixels[0] &= two_colour_mask_;

				target[0] = palette[(pixels[0] & 0x80) >> 7];
				target[1] = palette[(pixels[0] & 0x40) >> 6];
				target[2] = palette[(pixels[0] & 0x20) >> 5];
				target[3] = palette[(pixels[0] & 0x10) >> 4];
				target[4] = palette[(pixels[0] & 0x08) >> 3];
				target[5] = palette[(pixels[0] & 0x04) >> 2];
				target[6] = palette[(pixels[0] & 0x02) >> 1];
				target[7] = palette[(pixels[0] & 0x01) >> 0];

				if constexpr (!is_lpixel) {
					palette = alt_ind_palettes[((pixels[1] >> 6) & 0x02) | (pixels[1]&1)];
					pixels[1] &= two_colour_mask_;

					target[8] = palette[(pixels[1] & 0x80) >> 7];
					target[9] = palette[(pixels[1] & 0x40) >> 6];
					target[10] = palette[(pixels[1] & 0x20) >> 5];
					target[11] = palette[(pixels[1] & 0x10) >> 4];
					target[12] = palette[(pixels[1] & 0x08) >> 3];
					target[13] = palette[(pixels[1] & 0x04) >> 2];
					target[14] = palette[(pixels[1] & 0x02) >> 1];
					target[15] = palette[(pixels[1] & 0x01) >> 0];

					target += 8;
				}

				target += 8;
			} break;

			case 2:
				target[0] = palette_[((pixels[0] & 0x80) >> 6) | ((pixels[0] & 0x08) >> 3)];
				target[1] = palette_[((pixels[0] & 0x40) >> 5) | ((pixels[0] & 0x04) >> 2)];
				target[2] = palette_[((pixels[0] & 0x20) >> 4) | ((pixels[0] & 0x02) >> 1)];
				target[3] = palette_[((pixels[0] & 0x10) >> 3) | ((pixels[0] & 0x01) >> 0)];

				if constexpr (!is_lpixel) {
					target[4] = palette_[((pixels[1] & 0x80) >> 6) | ((pixels[1] & 0x08) >> 3)];
					target[5] = palette_[((pixels[1] & 0x40) >> 5) | ((pixels[1] & 0x04) >> 2)];
					target[6] = palette_[((pixels[1] & 0x20) >> 4) | ((pixels[1] & 0x02) >> 1)];
					target[7] = palette_[((pixels[1] & 0x10) >> 3) | ((pixels[1] & 0x01) >> 0)];

					target += 4;
				}

				target += 4;
			break;

			case 4:
				target[0] = palette_[((pixels[0] & 0x80) >> 4) | ((pixels[0] & 0x20) >> 3) | ((pixels[0] & 0x08) >> 2) | ((pixels[0] & 0x02) >> 1)];
				target[1] = palette_[((pixels[0] & 0x40) >> 3) | ((pixels[0] & 0x10) >> 2) | ((pixels[0] & 0x04) >> 1) | ((pixels[0] & 0x01) >> 0)];

				if constexpr (!is_lpixel) {
					target[2] = palette_[((pixels[1] & 0x80) >> 4) | ((pixels[1] & 0x20) >> 3) | ((pixels[1] & 0x08) >> 2) | ((pixels[1] & 0x02) >> 1)];
					target[3] = palette_[((pixels[1] & 0x40) >> 3) | ((pixels[1] & 0x10) >> 2) | ((pixels[1] & 0x04) >> 1) | ((pixels[1] & 0x01) >> 0)];

					target += 2;
				}

				target += 2;
			break;

			case 8:
				target[0] = mapped_colour(pixels[0]);

				if constexpr (!is_lpixel) {
					target[1] = mapped_colour(pixels[1]);

					++target;
				}
				++target;
			break;
		}
	}
}

template <int bpp, int index_bits> void Nick::output_character(uint16_t *target, int columns) {
	static_assert(bpp == 1 || bpp == 2 || bpp == 4 || bpp == 8);

	for(int c = 0; c < columns; c++) {
		const uint8_t character = ram_[line_data_pointer_[0]];
		++line_data_pointer_[0];

		const uint8_t pixels = ram_[
			(line_data_pointer_[1] << index_bits) +
			(character & ((1 << index_bits) - 1))
		];

		// TODO: below looks repetitious of the above, but I've yet to factor in
		// ALTINDs and [M/L]SBALTs, so I'll correct for factoring when I've done that.

		switch(bpp) {
			default:
				assert(false);
			break;

			case 1: {
				// This applies ALTIND0 and ALTIND1.
				const uint16_t *palette = alt_ind_palettes[character >> 6];
				target[0] = palette[(pixels & 0x80) >> 7];
				target[1] = palette[(pixels & 0x40) >> 6];
				target[2] = palette[(pixels & 0x20) >> 5];
				target[3] = palette[(pixels & 0x10) >> 4];
				target[4] = palette[(pixels & 0x08) >> 3];
				target[5] = palette[(pixels & 0x04) >> 2];
				target[6] = palette[(pixels & 0x02) >> 1];
				target[7] = palette[(pixels & 0x01) >> 0];
				target += 8;
			} break;
		}
	}
}

template <int bpp> void Nick::output_attributed(uint16_t *target, int columns) {
	static_assert(bpp == 1 || bpp == 2 || bpp == 4 || bpp == 8);

	for(int c = 0; c < columns; c++) {
		const uint8_t pixels = ram_[line_data_pointer_[1]];
		const uint8_t attributes = ram_[line_data_pointer_[0]];

		++line_data_pointer_[0];
		++line_data_pointer_[1];

		const uint16_t palette[2] = {
			palette_[attributes >> 4], palette_[attributes & 0x0f]
		};

		target[0] = palette[(pixels & 0x80) >> 7];
		target[1] = palette[(pixels & 0x40) >> 6];
		target[2] = palette[(pixels & 0x20) >> 5];
		target[3] = palette[(pixels & 0x10) >> 4];
		target[4] = palette[(pixels & 0x08) >> 3];
		target[5] = palette[(pixels & 0x04) >> 2];
		target[6] = palette[(pixels & 0x02) >> 1];
		target[7] = palette[(pixels & 0x01) >> 0];
		target += 8;
	}
}