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338 lines
13 KiB
C++
338 lines
13 KiB
C++
//
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// Video.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 14/04/2018.
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// Copyright 2018 Thomas Harte. All rights reserved.
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//
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#ifndef Video_hpp
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#define Video_hpp
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#include "../../Outputs/CRT/CRT.hpp"
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#include "../../ClockReceiver/ClockReceiver.hpp"
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#include <vector>
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namespace AppleII {
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namespace Video {
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class BusHandler {
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public:
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uint8_t perform_read(uint16_t address) {
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return 0xff;
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}
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};
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class VideoBase {
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public:
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VideoBase();
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/// @returns The CRT this video feed is feeding.
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Outputs::CRT::CRT *get_crt();
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// Inputs for the various soft switches.
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void set_graphics_mode();
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void set_text_mode();
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void set_mixed_mode(bool);
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void set_video_page(int);
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void set_low_resolution();
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void set_high_resolution();
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// Setup for text mode.
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void set_character_rom(const std::vector<uint8_t> &);
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protected:
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std::unique_ptr<Outputs::CRT::CRT> crt_;
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uint8_t *pixel_pointer_ = nullptr;
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int pixel_pointer_column_ = 0;
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bool pixels_are_high_density_ = false;
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int video_page_ = 0;
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int row_ = 0, column_ = 0, flash_ = 0;
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std::vector<uint8_t> character_rom_;
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enum class GraphicsMode {
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LowRes,
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HighRes,
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Text
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} graphics_mode_ = GraphicsMode::LowRes;
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bool use_graphics_mode_ = false;
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bool mixed_mode_ = false;
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uint8_t graphics_carry_ = 0;
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};
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template <class BusHandler> class Video: public VideoBase {
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public:
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/// Constructs an instance of the video feed; a CRT is also created.
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Video(BusHandler &bus_handler) :
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VideoBase(),
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bus_handler_(bus_handler) {}
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/*!
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Advances time by @c cycles; expects to be fed by the CPU clock.
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Implicitly adds an extra half a colour clock at the end of every
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line.
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*/
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void run_for(const Cycles cycles) {
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/*
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Addressing scheme used throughout is that column 0 is the first column with pixels in it;
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row 0 is the first row with pixels in it.
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A frame is oriented around 65 cycles across, 262 lines down.
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*/
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static const int first_sync_line = 220; // A complete guess. Information needed.
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static const int first_sync_column = 49; // Also a guess.
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static const int sync_length = 4; // One of the two likely candidates.
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int int_cycles = cycles.as_int();
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while(int_cycles) {
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const int cycles_this_line = std::min(65 - column_, int_cycles);
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const int ending_column = column_ + cycles_this_line;
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if(row_ >= first_sync_line && row_ < first_sync_line + 3) {
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// In effect apply an XOR to HSYNC and VSYNC flags in order to include equalising
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// pulses (and hencce keep hsync approximately where it should be during vsync).
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const int blank_start = std::max(first_sync_column - sync_length, column_);
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const int blank_end = std::min(first_sync_column, ending_column);
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if(blank_end > blank_start) {
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if(blank_start > column_) {
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crt_->output_sync(static_cast<unsigned int>(blank_start - column_) * 14);
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}
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crt_->output_blank(static_cast<unsigned int>(blank_end - blank_start) * 14);
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if(blank_end < ending_column) {
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crt_->output_sync(static_cast<unsigned int>(ending_column - blank_end) * 14);
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}
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} else {
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crt_->output_sync(static_cast<unsigned int>(cycles_this_line) * 14);
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}
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} else {
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const GraphicsMode line_mode = use_graphics_mode_ ? graphics_mode_ : GraphicsMode::Text;
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// The first 40 columns are submitted to the CRT only upon completion;
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// they'll be either graphics or blank, depending on which side we are
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// of line 192.
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if(column_ < 40) {
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if(row_ < 192) {
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GraphicsMode pixel_mode = (!mixed_mode_ || row_ < 160) ? line_mode : GraphicsMode::Text;
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bool requires_high_density = pixel_mode != GraphicsMode::Text;
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if(!column_ || requires_high_density != pixels_are_high_density_) {
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if(column_) output_data_to_column(column_);
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pixel_pointer_ = crt_->allocate_write_area(561);
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pixel_pointer_column_ = column_;
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pixels_are_high_density_ = requires_high_density;
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graphics_carry_ = 0;
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}
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const int pixel_end = std::min(40, ending_column);
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const int character_row = row_ >> 3;
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const int pixel_row = row_ & 7;
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const uint16_t row_address = static_cast<uint16_t>((character_row >> 3) * 40 + ((character_row&7) << 7));
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const uint16_t text_address = static_cast<uint16_t>(((video_page_+1) * 0x400) + row_address);
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switch(pixel_mode) {
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case GraphicsMode::Text: {
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const uint8_t inverses[] = {
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0xff,
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static_cast<uint8_t>((flash_ / flash_length) * 0xff),
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0x00,
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0x00
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};
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for(int c = column_; c < pixel_end; ++c) {
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const uint8_t character = bus_handler_.perform_read(static_cast<uint16_t>(text_address + c));
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const std::size_t character_address = static_cast<std::size_t>(((character & 0x3f) << 3) + pixel_row);
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const uint8_t character_pattern = character_rom_[character_address] ^ inverses[character >> 6];
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// The character ROM is output MSB to LSB rather than LSB to MSB.
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pixel_pointer_[0] = character_pattern & 0x40;
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pixel_pointer_[1] = character_pattern & 0x20;
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pixel_pointer_[2] = character_pattern & 0x10;
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pixel_pointer_[3] = character_pattern & 0x08;
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pixel_pointer_[4] = character_pattern & 0x04;
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pixel_pointer_[5] = character_pattern & 0x02;
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pixel_pointer_[6] = character_pattern & 0x01;
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graphics_carry_ = character_pattern & 0x40;
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pixel_pointer_ += 7;
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}
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} break;
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case GraphicsMode::LowRes: {
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const int row_shift = (row_&4);
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// TODO: decompose into two loops, possibly.
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for(int c = column_; c < pixel_end; ++c) {
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const uint8_t nibble = (bus_handler_.perform_read(static_cast<uint16_t>(text_address + c)) >> row_shift) & 0x0f;
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// Low-resolution graphics mode shifts the colour code on a loop, but has to account for whether this
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// 14-sample output window is starting at the beginning of a colour cycle or halfway through.
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if(c&1) {
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pixel_pointer_[0] = pixel_pointer_[4] = pixel_pointer_[8] = pixel_pointer_[12] = nibble & 4;
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pixel_pointer_[1] = pixel_pointer_[5] = pixel_pointer_[9] = pixel_pointer_[13] = nibble & 8;
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pixel_pointer_[2] = pixel_pointer_[6] = pixel_pointer_[10] = nibble & 1;
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pixel_pointer_[3] = pixel_pointer_[7] = pixel_pointer_[11] = nibble & 2;
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graphics_carry_ = nibble & 8;
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} else {
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pixel_pointer_[0] = pixel_pointer_[4] = pixel_pointer_[8] = pixel_pointer_[12] = nibble & 1;
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pixel_pointer_[1] = pixel_pointer_[5] = pixel_pointer_[9] = pixel_pointer_[13] = nibble & 2;
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pixel_pointer_[2] = pixel_pointer_[6] = pixel_pointer_[10] = nibble & 4;
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pixel_pointer_[3] = pixel_pointer_[7] = pixel_pointer_[11] = nibble & 8;
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graphics_carry_ = nibble & 2;
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}
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pixel_pointer_ += 14;
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}
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} break;
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case GraphicsMode::HighRes: {
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const uint16_t graphics_address = static_cast<uint16_t>(((video_page_+1) * 0x2000) + row_address + ((pixel_row&7) << 10));
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for(int c = column_; c < pixel_end; ++c) {
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const uint8_t graphic = bus_handler_.perform_read(static_cast<uint16_t>(graphics_address + c));
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// High resolution graphics shift out LSB to MSB, optionally with a delay of half a pixel.
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// If there is a delay, the previous output level is held to bridge the gap.
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if(graphic & 0x80) {
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pixel_pointer_[0] = graphics_carry_;
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pixel_pointer_[1] = pixel_pointer_[2] = graphic & 0x01;
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pixel_pointer_[3] = pixel_pointer_[4] = graphic & 0x02;
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pixel_pointer_[5] = pixel_pointer_[6] = graphic & 0x04;
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pixel_pointer_[7] = pixel_pointer_[8] = graphic & 0x08;
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pixel_pointer_[9] = pixel_pointer_[10] = graphic & 0x10;
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pixel_pointer_[11] = pixel_pointer_[12] = graphic & 0x20;
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pixel_pointer_[13] = graphic & 0x40;
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} else {
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pixel_pointer_[0] = pixel_pointer_[1] = graphic & 0x01;
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pixel_pointer_[2] = pixel_pointer_[3] = graphic & 0x02;
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pixel_pointer_[4] = pixel_pointer_[5] = graphic & 0x04;
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pixel_pointer_[6] = pixel_pointer_[7] = graphic & 0x08;
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pixel_pointer_[8] = pixel_pointer_[9] = graphic & 0x10;
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pixel_pointer_[10] = pixel_pointer_[11] = graphic & 0x20;
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pixel_pointer_[12] = pixel_pointer_[13] = graphic & 0x40;
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}
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graphics_carry_ = graphic & 0x40;
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pixel_pointer_ += 14;
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}
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} break;
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}
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if(ending_column >= 40) {
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output_data_to_column(40);
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}
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} else {
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if(ending_column >= 40) {
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crt_->output_blank(560);
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}
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}
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}
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/*
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The left border, sync, right border pattern doesn't depend on whether
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there were pixels this row and is output as soon as it is known.
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*/
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const int first_blank_start = std::max(40, column_);
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const int first_blank_end = std::min(first_sync_column, ending_column);
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if(first_blank_end > first_blank_start) {
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crt_->output_blank(static_cast<unsigned int>(first_blank_end - first_blank_start) * 14);
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}
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const int sync_start = std::max(first_sync_column, column_);
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const int sync_end = std::min(first_sync_column + sync_length, ending_column);
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if(sync_end > sync_start) {
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crt_->output_sync(static_cast<unsigned int>(sync_end - sync_start) * 14);
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}
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int second_blank_start;
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if(line_mode != GraphicsMode::Text && (!mixed_mode_ || row_ < 159 || row_ >= 192)) {
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const int colour_burst_start = std::max(first_sync_column + sync_length + 1, column_);
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const int colour_burst_end = std::min(first_sync_column + sync_length + 4, ending_column);
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if(colour_burst_end > colour_burst_start) {
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crt_->output_default_colour_burst(static_cast<unsigned int>(colour_burst_end - colour_burst_start) * 14);
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}
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second_blank_start = std::max(first_sync_column + 7, column_);
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} else {
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second_blank_start = std::max(first_sync_column + 4, column_);
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}
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if(ending_column > second_blank_start) {
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crt_->output_blank(static_cast<unsigned int>(ending_column - second_blank_start) * 14);
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}
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}
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int_cycles -= cycles_this_line;
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column_ = (column_ + cycles_this_line) % 65;
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if(!column_) {
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row_ = (row_ + 1) % 262;
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flash_ = (flash_ + 1) % (2 * flash_length);
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// Add an extra half a colour cycle of blank; this isn't counted in the run_for
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// count explicitly but is promised.
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crt_->output_blank(2);
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}
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}
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}
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/*!
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Obtains the last value the video read prior to time now+offset.
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*/
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uint8_t get_last_read_value(Cycles offset) {
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// Rules of generation:
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// (1) a complete sixty-five-cycle scan line consists of sixty-five consecutive bytes of
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// display buffer memory that starts twenty-five bytes prior to the actual data to be displayed.
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// (2) During VBL the data acts just as if it were starting a whole new frame from the beginning, but
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// it never finishes this pseudo-frame. After getting one third of the way through the frame (to
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// scan line $3F), it suddenly repeats the previous six scan lines ($3A through $3F) before aborting
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// to begin the next true frame.
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//
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// Source: Have an Apple Split by Bob Bishop; http://rich12345.tripod.com/aiivideo/softalk.html
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// Determine column at offset.
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int mapped_column = column_ + offset.as_int();
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// Map that backwards from the internal pixels-at-start generation to pixels-at-end
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// (so what was column 0 is now column 25).
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mapped_column += 25;
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// Apply carry into the row counter.
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int mapped_row = row_ + (mapped_column / 65);
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mapped_column %= 65;
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mapped_row %= 262;
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// Apple out-of-bounds row logic.
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if(mapped_row >= 256) {
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mapped_row = 0x3a + (mapped_row&255);
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} else {
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mapped_row %= 192;
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}
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// Calculate the address and return the value.
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uint16_t read_address = static_cast<uint16_t>(get_row_address(mapped_row) + mapped_column - 25);
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return bus_handler_.perform_read(read_address);
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}
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private:
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uint16_t get_row_address(int row) {
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const int character_row = row >> 3;
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const int pixel_row = row & 7;
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const uint16_t row_address = static_cast<uint16_t>((character_row >> 3) * 40 + ((character_row&7) << 7));
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GraphicsMode pixel_mode = ((!mixed_mode_ || row < 160) && use_graphics_mode_) ? graphics_mode_ : GraphicsMode::Text;
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return (pixel_mode == GraphicsMode::HighRes) ?
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static_cast<uint16_t>(((video_page_+1) * 0x2000) + row_address + ((pixel_row&7) << 10)) :
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static_cast<uint16_t>(((video_page_+1) * 0x400) + row_address);
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}
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static const int flash_length = 8406;
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BusHandler &bus_handler_;
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void output_data_to_column(int column) {
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int length = column - pixel_pointer_column_;
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crt_->output_data(static_cast<unsigned int>(length*14), static_cast<unsigned int>(length * (pixels_are_high_density_ ? 14 : 7)));
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pixel_pointer_ = nullptr;
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}
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};
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}
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}
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#endif /* Video_hpp */
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