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189 lines
6.3 KiB
C++
189 lines
6.3 KiB
C++
//
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// Video.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 03/05/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#include "Video.hpp"
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#include <algorithm>
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using namespace Apple::Macintosh;
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// Re: CRT timings, see the Apple Guide to the Macintosh Hardware Family,
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// bottom of page 400:
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//
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// "For each scan line, 512 pixels are drawn on the screen ...
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// The horizontal blanking interval takes the time of an additional 192 pixels"
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//
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// And, at the top of 401:
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//
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// "The visible portion of a full-screen display consists of 342 horizontal scan lines...
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// During the vertical blanking interval, the turned-off beam ... traces out an additional 28 scan lines,"
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//
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Video::Video(DeferredAudio &audio, DriveSpeedAccumulator &drive_speed_accumulator) :
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audio_(audio),
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drive_speed_accumulator_(drive_speed_accumulator),
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crt_(704, 1, 370, 6, Outputs::Display::InputDataType::Luminance1) {
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crt_.set_display_type(Outputs::Display::DisplayType::RGB);
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crt_.set_visible_area(Outputs::Display::Rect(0.08f, -0.025f, 0.82f, 0.82f));
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crt_.set_aspect_ratio(1.73f); // The Mac uses a non-standard scanning area.
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}
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void Video::set_scan_target(Outputs::Display::ScanTarget *scan_target) {
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crt_.set_scan_target(scan_target);
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}
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Outputs::Display::ScanStatus Video::get_scaled_scan_status() const {
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return crt_.get_scaled_scan_status() / 2.0f;
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}
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void Video::run_for(HalfCycles duration) {
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// Determine the current video and audio bases. These values don't appear to be latched, they apply immediately.
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const size_t video_base = (use_alternate_screen_buffer_ ? (0xffff2700 >> 1) : (0xffffa700 >> 1)) & ram_mask_;
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const size_t audio_base = (use_alternate_audio_buffer_ ? (0xffffa100 >> 1) : (0xfffffd00 >> 1)) & ram_mask_;
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// The number of HalfCycles is literally the number of pixel clocks to move through,
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// since pixel output occurs at twice the processor clock. So divide by 16 to get
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// the number of fetches.
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while(duration > HalfCycles(0)) {
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const auto pixel_start = frame_position_ % line_length;
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const int line = int((frame_position_ / line_length).as_integral());
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const auto cycles_left_in_line = std::min(line_length - pixel_start, duration);
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// Line timing, entirely invented as I can find exactly zero words of documentation:
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//
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// First 342 lines:
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//
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// First 32 words = pixels;
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// next 5 words = right border;
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// next 2 words = sync level;
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// final 5 words = left border.
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//
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// Then 12 lines of border, 3 of sync, 11 more of border.
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const int first_word = int(pixel_start.as_integral()) >> 4;
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const int final_word = int((pixel_start + cycles_left_in_line).as_integral()) >> 4;
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if(first_word != final_word) {
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if(line < 342) {
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// If there are any pixels left to output, do so.
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if(first_word < 32) {
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const int final_pixel_word = std::min(final_word, 32);
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if(!first_word) {
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pixel_buffer_ = crt_.begin_data(512);
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}
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if(pixel_buffer_) {
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for(int c = first_word; c < final_pixel_word; ++c) {
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uint16_t pixels = ram_[video_base + video_address_] ^ 0xffff;
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++video_address_;
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pixel_buffer_[15] = pixels & 0x01;
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pixel_buffer_[14] = pixels & 0x02;
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pixel_buffer_[13] = pixels & 0x04;
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pixel_buffer_[12] = pixels & 0x08;
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pixel_buffer_[11] = pixels & 0x10;
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pixel_buffer_[10] = pixels & 0x20;
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pixel_buffer_[9] = pixels & 0x40;
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pixel_buffer_[8] = pixels & 0x80;
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pixels >>= 8;
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pixel_buffer_[7] = pixels & 0x01;
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pixel_buffer_[6] = pixels & 0x02;
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pixel_buffer_[5] = pixels & 0x04;
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pixel_buffer_[4] = pixels & 0x08;
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pixel_buffer_[3] = pixels & 0x10;
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pixel_buffer_[2] = pixels & 0x20;
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pixel_buffer_[1] = pixels & 0x40;
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pixel_buffer_[0] = pixels & 0x80;
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pixel_buffer_ += 16;
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}
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}
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if(final_pixel_word == 32) {
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crt_.output_data(512);
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}
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}
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if(first_word < sync_start && final_word >= sync_start) crt_.output_blank((sync_start - 32) * 16);
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if(first_word < sync_end && final_word >= sync_end) crt_.output_sync((sync_end - sync_start) * 16);
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if(final_word == 44) crt_.output_blank((44 - sync_end) * 16);
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} else if(final_word == 44) {
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if(line >= 353 && line < 356) {
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/* Output a sync line. */
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crt_.output_sync(sync_start * 16);
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crt_.output_blank((sync_end - sync_start) * 16);
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crt_.output_sync((44 - sync_end) * 16);
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} else {
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/* Output a blank line. */
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crt_.output_blank(sync_start * 16);
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crt_.output_sync((sync_end - sync_start) * 16);
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crt_.output_blank((44 - sync_end) * 16);
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}
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}
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// Audio and disk fetches occur "just before video data".
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if(final_word == 44) {
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const uint16_t audio_word = ram_[audio_address_ + audio_base];
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++audio_address_;
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audio_.audio.post_sample(audio_word >> 8);
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drive_speed_accumulator_.post_sample(audio_word & 0xff);
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}
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}
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duration -= cycles_left_in_line;
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frame_position_ = frame_position_ + cycles_left_in_line;
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if(frame_position_ == frame_length) {
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frame_position_ = HalfCycles(0);
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/*
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Video: $1A700 and the alternate buffer starts at $12700; for a 512K Macintosh, add $60000 to these numbers.
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*/
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video_address_ = 0;
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/*
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"The main sound buffer is at $1FD00 in a 128K Macintosh, and the alternate buffer is at $1A100;
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for a 512K Macintosh, add $60000 to these values."
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*/
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audio_address_ = 0;
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}
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}
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}
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bool Video::vsync() {
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const auto line = (frame_position_ / line_length).as_integral();
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return line >= 353 && line < 356;
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}
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HalfCycles Video::get_next_sequence_point() {
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const auto line = (frame_position_ / line_length).as_integral();
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if(line >= 353 && line < 356) {
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// Currently in vsync, so get time until start of line 357,
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// when vsync will end.
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return HalfCycles(356) * line_length - frame_position_;
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} else {
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// Not currently in vsync, so get time until start of line 353.
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const auto start_of_vsync = HalfCycles(353) * line_length;
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if(frame_position_ < start_of_vsync)
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return start_of_vsync - frame_position_;
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else
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return start_of_vsync + HalfCycles(number_of_lines) * line_length - frame_position_;
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}
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}
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void Video::set_use_alternate_buffers(bool use_alternate_screen_buffer, bool use_alternate_audio_buffer) {
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use_alternate_screen_buffer_ = use_alternate_screen_buffer;
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use_alternate_audio_buffer_ = use_alternate_audio_buffer;
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}
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void Video::set_ram(uint16_t *ram, uint32_t mask) {
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ram_ = ram;
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ram_mask_ = mask;
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}
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