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451 lines
14 KiB
C++
451 lines
14 KiB
C++
//
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// CGA.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/12/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#ifndef CGA_h
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#define CGA_h
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#include "../../Components/6845/CRTC6845.hpp"
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#include "../../Outputs/CRT/CRT.hpp"
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#include "../../Machines/Utility/ROMCatalogue.hpp"
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namespace PCCompatible {
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class CGA {
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public:
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CGA() : crtc_(Motorola::CRTC::Personality::HD6845S, outputter_) {}
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static constexpr uint32_t BaseAddress = 0xb'8000;
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static constexpr auto FontROM = ROM::Name::PCCompatibleCGAFont;
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void set_source(const uint8_t *ram, std::vector<uint8_t> font) {
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outputter_.ram = ram;
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outputter_.font = font;
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}
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void run_for(Cycles cycles) {
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// Input rate is the PIT rate of 1,193,182 Hz.
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// CGA is clocked at the real oscillator rate of 12 times that.
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// But there's also an internal divide by 8 to align to the 80-cfetch clock.
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// ... and 12/8 = 3/2.
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full_clock_ += 3 * cycles.as<int>();
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const int modulo = 2 * outputter_.clock_divider;
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crtc_.run_for(Cycles(full_clock_ / modulo));
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full_clock_ %= modulo;
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}
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template <int address>
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void write(uint8_t value) {
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switch(address) {
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case 0: case 2: case 4: case 6:
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crtc_.select_register(value);
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break;
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case 1: case 3: case 5: case 7:
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crtc_.set_register(value);
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break;
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case 0x8: outputter_.set_mode(value); break;
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case 0x9: outputter_.set_colours(value); break;
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}
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}
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template <int address>
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uint8_t read() {
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switch(address) {
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case 1: case 3: case 5: case 7:
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return crtc_.get_register();
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case 0xa:
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return
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// b3: 1 => in vsync; 0 => not;
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// b2: 1 => light pen switch is off;
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// b1: 1 => positive edge from light pen has set trigger;
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// b0: 1 => safe to write to VRAM now without causing snow.
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(crtc_.get_bus_state().vsync ? 0b1001 : 0b0000) |
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(crtc_.get_bus_state().display_enable ? 0b0000 : 0b0001) |
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0b0100;
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default: return 0xff;
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}
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}
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// MARK: - Display type configuration.
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void set_display_type(Outputs::Display::DisplayType display_type) {
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outputter_.crt.set_display_type(display_type);
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outputter_.set_is_composite(Outputs::Display::is_composite(display_type));
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}
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Outputs::Display::DisplayType get_display_type() const {
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return outputter_.crt.get_display_type();
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}
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// MARK: - Call-ins for ScanProducer.
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void set_scan_target(Outputs::Display::ScanTarget *scan_target) {
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outputter_.crt.set_scan_target(scan_target);
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}
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Outputs::Display::ScanStatus get_scaled_scan_status() const {
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// The CRT is always handed data at the full CGA pixel clock rate, so just
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// divide by 12 to get back to the rate that run_for is being called at.
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return outputter_.crt.get_scaled_scan_status() / 12.0f;
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}
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private:
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struct CRTCOutputter {
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enum class OutputState {
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Sync, Pixels, Border, ColourBurst
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};
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CRTCOutputter() :
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crt(910, 8, Outputs::Display::Type::NTSC60, Outputs::Display::InputDataType::Red2Green2Blue2)
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{
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crt.set_visible_area(Outputs::Display::Rect(0.097f, 0.095f, 0.82f, 0.82f));
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crt.set_display_type(Outputs::Display::DisplayType::RGB);
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}
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void set_mode(uint8_t control) {
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// b5: enable blink
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// b4: 1 => 640x200 graphics
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// b3: video enable
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// b2: 1 => monochrome
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// b1: 1 => 320x200 graphics; 0 => text
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// b0: 1 => 80-column text; 0 => 40
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control_ = control; // To capture blink, monochrome and video enable bits.
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if(control & 0x2) {
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mode_ = (control & 0x10) ? Mode::Pixels640 : Mode::Pixels320;
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pixels_per_tick = (mode_ == Mode::Pixels640) ? 16 : 8;
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} else {
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mode_ = Mode::Text;
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pixels_per_tick = 8;
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}
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clock_divider = 1 + !(control & 0x01);
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// Both graphics mode and monochrome/colour may have changed, so update the palette.
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update_palette();
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}
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void set_is_composite(bool is_composite) {
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is_composite_ = is_composite;
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update_palette();
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}
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void set_colours(uint8_t value) {
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colours_ = value;
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update_palette();
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}
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uint8_t control() {
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return control_;
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}
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void update_hsync(bool new_hsync) {
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if(new_hsync == previous_hsync) {
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cycles_since_hsync += clock_divider;
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} else {
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cycles_since_hsync = 0;
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previous_hsync = new_hsync;
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}
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}
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OutputState implied_state(const Motorola::CRTC::BusState &state) const {
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OutputState new_state;
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if(state.hsync || state.vsync) {
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new_state = OutputState::Sync;
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} else if(!state.display_enable || !(control_&0x08)) {
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new_state = OutputState::Border;
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// TODO: this isn't correct for colour burst positioning, though
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// it happens to fool the particular CRT I've implemented.
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if(!(control_&4) && cycles_since_hsync <= 6) {
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new_state = OutputState::ColourBurst;
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}
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} else {
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new_state = OutputState::Pixels;
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}
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return new_state;
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}
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void perform_bus_cycle_phase1(const Motorola::CRTC::BusState &state) {
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// Determine new output state.
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update_hsync(state.hsync);
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const OutputState new_state = implied_state(state);
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static constexpr uint8_t colour_phase = 200;
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// Upon either a state change or just having accumulated too much local time...
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if(
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new_state != output_state ||
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active_pixels_per_tick != pixels_per_tick ||
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active_clock_divider != clock_divider ||
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active_border_colour != border_colour ||
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count > 912
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) {
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// (1) flush preexisting state.
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if(count) {
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switch(output_state) {
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case OutputState::Sync: crt.output_sync(count * active_clock_divider); break;
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case OutputState::Border:
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if(active_border_colour) {
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crt.output_blank(count * active_clock_divider);
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} else {
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crt.output_level<uint8_t>(count * active_clock_divider, active_border_colour);
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}
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break;
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case OutputState::ColourBurst: crt.output_colour_burst(count * active_clock_divider, colour_phase); break;
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case OutputState::Pixels: flush_pixels(); break;
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}
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}
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// (2) adopt new state.
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output_state = new_state;
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active_pixels_per_tick = pixels_per_tick;
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active_clock_divider = clock_divider;
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active_border_colour = border_colour;
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count = 0;
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}
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// Collect pixels if applicable.
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if(output_state == OutputState::Pixels) {
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if(!pixels) {
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pixel_pointer = pixels = crt.begin_data(DefaultAllocationSize);
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// Flush any period where pixels weren't recorded due to back pressure.
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if(pixels && count) {
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crt.output_blank(count * active_clock_divider);
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count = 0;
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}
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}
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if(pixels) {
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if(state.cursor) {
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std::fill(pixel_pointer, pixel_pointer + pixels_per_tick, 0x3f); // i.e. white.
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} else {
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if(mode_ == Mode::Text) {
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serialise_text(state);
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} else {
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serialise_pixels(state);
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}
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}
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pixel_pointer += active_pixels_per_tick;
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}
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}
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// Advance.
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count += 8;
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// Output pixel row prematurely if storage is exhausted.
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if(output_state == OutputState::Pixels && pixel_pointer == pixels + DefaultAllocationSize) {
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flush_pixels();
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count = 0;
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}
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}
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void perform_bus_cycle_phase2(const Motorola::CRTC::BusState &) {}
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void flush_pixels() {
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crt.output_data(count * active_clock_divider, size_t((count * active_pixels_per_tick) / 8));
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pixels = pixel_pointer = nullptr;
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}
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void serialise_pixels(const Motorola::CRTC::BusState &state) {
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// This is what I think is happenings:
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//
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// Refresh address is still shifted left one and two bytes are fetched, just as if it were
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// character code + attributes except that these are two bytes worth of graphics.
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//
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// Meanwhile, row address is used to invent a 15th address line.
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const auto base_address =
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((state.refresh_address & 0xfff) << 1) +
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((state.row_address & 1) << 13);
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const uint8_t bitmap[] = {
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ram[base_address],
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ram[base_address + 1],
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};
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if(mode_ == Mode::Pixels320) {
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pixel_pointer[0] = palette320[(bitmap[0] & 0xc0) >> 6];
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pixel_pointer[1] = palette320[(bitmap[0] & 0x30) >> 4];
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pixel_pointer[2] = palette320[(bitmap[0] & 0x0c) >> 2];
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pixel_pointer[3] = palette320[(bitmap[0] & 0x03) >> 0];
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pixel_pointer[4] = palette320[(bitmap[1] & 0xc0) >> 6];
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pixel_pointer[5] = palette320[(bitmap[1] & 0x30) >> 4];
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pixel_pointer[6] = palette320[(bitmap[1] & 0x0c) >> 2];
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pixel_pointer[7] = palette320[(bitmap[1] & 0x03) >> 0];
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} else {
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pixel_pointer[0x0] = palette640[(bitmap[0] & 0x80) >> 7];
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pixel_pointer[0x1] = palette640[(bitmap[0] & 0x40) >> 6];
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pixel_pointer[0x2] = palette640[(bitmap[0] & 0x20) >> 5];
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pixel_pointer[0x3] = palette640[(bitmap[0] & 0x10) >> 4];
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pixel_pointer[0x4] = palette640[(bitmap[0] & 0x08) >> 3];
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pixel_pointer[0x5] = palette640[(bitmap[0] & 0x04) >> 2];
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pixel_pointer[0x6] = palette640[(bitmap[0] & 0x02) >> 1];
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pixel_pointer[0x7] = palette640[(bitmap[0] & 0x01) >> 0];
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pixel_pointer[0x8] = palette640[(bitmap[1] & 0x80) >> 7];
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pixel_pointer[0x9] = palette640[(bitmap[1] & 0x40) >> 6];
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pixel_pointer[0xa] = palette640[(bitmap[1] & 0x20) >> 5];
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pixel_pointer[0xb] = palette640[(bitmap[1] & 0x10) >> 4];
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pixel_pointer[0xc] = palette640[(bitmap[1] & 0x08) >> 3];
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pixel_pointer[0xd] = palette640[(bitmap[1] & 0x04) >> 2];
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pixel_pointer[0xe] = palette640[(bitmap[1] & 0x02) >> 1];
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pixel_pointer[0xf] = palette640[(bitmap[1] & 0x01) >> 0];
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}
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}
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void serialise_text(const Motorola::CRTC::BusState &state) {
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const uint8_t attributes = ram[((state.refresh_address << 1) + 1) & 0x3fff];
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const uint8_t glyph = ram[((state.refresh_address << 1) + 0) & 0x3fff];
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const uint8_t row = font[(glyph * 8) + state.row_address];
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uint8_t colours[2] = { rgb(attributes >> 4), rgbi(attributes) };
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// Apply blink or background intensity.
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if(control_ & 0x20) {
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// Set both colours to black if within a blink; otherwise consider a yellow-to-brown conversion.
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if((attributes & 0x80) && (state.field_count & 16)) {
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colours[0] = colours[1] = 0;
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} else {
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colours[0] = yellow_to_brown(colours[0]);
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}
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} else {
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if(attributes & 0x80) {
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colours[0] = bright(colours[0]);
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} else {
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// Yellow to brown definitely doesn't apply if the colour has been brightened.
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colours[0] = yellow_to_brown(colours[0]);
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}
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}
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// Draw according to ROM contents.
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pixel_pointer[0] = (row & 0x80) ? colours[1] : colours[0];
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pixel_pointer[1] = (row & 0x40) ? colours[1] : colours[0];
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pixel_pointer[2] = (row & 0x20) ? colours[1] : colours[0];
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pixel_pointer[3] = (row & 0x10) ? colours[1] : colours[0];
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pixel_pointer[4] = (row & 0x08) ? colours[1] : colours[0];
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pixel_pointer[5] = (row & 0x04) ? colours[1] : colours[0];
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pixel_pointer[6] = (row & 0x02) ? colours[1] : colours[0];
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pixel_pointer[7] = (row & 0x01) ? colours[1] : colours[0];
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}
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Outputs::CRT::CRT crt;
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static constexpr size_t DefaultAllocationSize = 320;
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// Current output stream.
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uint8_t *pixels = nullptr;
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uint8_t *pixel_pointer = nullptr;
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int active_pixels_per_tick = 8;
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int active_clock_divider = 1;
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uint8_t active_border_colour = 0;
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// Source data.
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const uint8_t *ram = nullptr;
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std::vector<uint8_t> font;
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// CRTC state tracking, for CRT serialisation.
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OutputState output_state = OutputState::Sync;
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int count = 0;
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bool previous_hsync = false;
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int cycles_since_hsync = 0;
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// Current Programmer-set parameters.
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int clock_divider = 1;
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int pixels_per_tick = 8;
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uint8_t colours_ = 0;
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uint8_t control_ = 0;
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bool is_composite_ = false;
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enum class Mode {
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Pixels640, Pixels320, Text,
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} mode_ = Mode::Text;
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uint8_t palette320[4]{};
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uint8_t palette640[2]{};
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uint8_t border_colour;
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void update_palette() {
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// b5: 320x200 palette, unless in monochrome mode.
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if(control_ & 0x04) {
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palette320[1] = DarkCyan;
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palette320[2] = DarkRed;
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palette320[3] = DarkGrey;
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} else {
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if(colours_ & 0x20) {
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palette320[1] = DarkCyan;
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palette320[2] = DarkMagenta;
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palette320[3] = DarkGrey;
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} else {
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palette320[1] = DarkGreen;
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palette320[2] = DarkRed;
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palette320[3] = DarkYellow;
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}
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}
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// b4: set 320x200 palette into high intensity.
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if(colours_ & 0x10) {
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palette320[1] = bright(palette320[1]);
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palette320[2] = bright(palette320[2]);
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palette320[3] = bright(palette320[3]);
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} else {
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// Remap dark yellow to brown if applicable.
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palette320[3] = yellow_to_brown(palette320[3]);
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}
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// b3–b0: set background, border, monochrome colour.
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palette640[1] = palette320[0] = rgbi(colours_);
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border_colour = (mode_ != Mode::Pixels640) ? palette320[0] : 0;
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}
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//
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// Named colours and mapping logic.
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//
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static constexpr uint8_t DarkCyan = 0b00'10'10;
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static constexpr uint8_t DarkMagenta = 0b10'00'10;
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static constexpr uint8_t DarkGrey = 0b10'10'10;
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static constexpr uint8_t DarkGreen = 0b00'10'00;
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static constexpr uint8_t DarkRed = 0b10'00'00;
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static constexpr uint8_t DarkYellow = 0b10'10'00;
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static constexpr uint8_t Brown = 0b10'01'00;
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/// @returns @c Brown if @c source is @c DarkYellow and composite output is not enabled; @c source otherwise.
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constexpr uint8_t yellow_to_brown(uint8_t source) {
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return (source == DarkYellow && !is_composite_) ? Brown : source;
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}
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/// @returns The brightened (i.e. high intensity) version of @c source.
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constexpr uint8_t bright(uint8_t source) {
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return source | (source >> 1);
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}
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/// Maps the RGB TTL triplet @c source to an appropriate output colour.
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constexpr uint8_t rgb(uint8_t source) {
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return uint8_t(
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((source & 0x01) << 1) |
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((source & 0x02) << 2) |
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((source & 0x04) << 3)
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);
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}
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/// Maps the RGBI value in @c source to an appropriate output colour, including potential yellow-to-brown conversion.
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constexpr uint8_t rgbi(uint8_t source) {
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const uint8_t result = rgb(source);
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return (source & 0x10) ? bright(result) : yellow_to_brown(result);
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}
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} outputter_;
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Motorola::CRTC::CRTC6845<CRTCOutputter, Motorola::CRTC::CursorType::MDA> crtc_;
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int full_clock_ = 0;
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};
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}
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#endif /* CGA_h */
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