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128 lines
3.6 KiB
C++
128 lines
3.6 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 31/10/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#ifndef Apple_IIgs_Video_hpp
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#define Apple_IIgs_Video_hpp
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#include "../AppleII/VideoSwitches.hpp"
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#include "../../../Outputs/CRT/CRT.hpp"
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#include "../../../ClockReceiver/ClockReceiver.hpp"
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namespace Apple {
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namespace IIgs {
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namespace Video {
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/*!
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Provides IIgs video output; assumed clocking here is twice the usual Apple II clock.
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So it'll produce a single line of video every 131 cycles — 65*2 + 1, allowing for the
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stretched cycle.
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*/
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class VideoBase: public Apple::II::VideoSwitches<Cycles> {
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public:
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VideoBase();
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void set_internal_ram(const uint8_t *);
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bool get_is_vertical_blank(Cycles offset);
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void set_new_video(uint8_t);
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uint8_t get_new_video();
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void clear_interrupts(uint8_t);
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uint8_t get_interrupt_register();
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void set_interrupt_register(uint8_t);
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void notify_clock_tick();
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void set_border_colour(uint8_t);
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void set_text_colour(uint8_t);
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void set_composite_is_colour(bool);
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bool get_composite_is_colour();
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/// Sets the scan target.
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void set_scan_target(Outputs::Display::ScanTarget *scan_target);
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/// Gets the current scan status.
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Outputs::Display::ScanStatus get_scaled_scan_status() const;
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/// Sets the type of output.
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void set_display_type(Outputs::Display::DisplayType);
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/// Gets the type of output.
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Outputs::Display::DisplayType get_display_type() const;
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/// Determines the period until video might autonomously update its interrupt lines.
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Cycles get_next_sequence_point() const;
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private:
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Outputs::CRT::CRT crt_;
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void advance(Cycles);
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uint8_t new_video_ = 0x01;
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uint8_t interrupts_ = 0x00;
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void set_interrupts(uint8_t);
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int cycles_into_frame_ = 0;
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const uint8_t *ram_ = nullptr;
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// The modal colours.
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uint16_t border_colour_ = 0;
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uint16_t text_colour_ = 0xffff;
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uint16_t background_colour_ = 0;
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// Current pixel output buffer.
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uint16_t *pixels_ = nullptr, *next_pixel_ = nullptr;
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void output_row(int row, int start, int end);
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uint16_t *output_super_high_res(uint16_t *target, int start, int end, int row) const;
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uint16_t *output_text(uint16_t *target, int start, int end, int row) const;
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uint16_t *output_double_text(uint16_t *target, int start, int end, int row) const;
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uint16_t *output_char(uint16_t *target, uint8_t source, int row) const;
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uint16_t *output_low_resolution(uint16_t *target, int start, int end, int row);
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uint16_t *output_high_resolution(uint16_t *target, int start, int end, int row);
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// Super high-res per-line state.
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uint8_t line_control_;
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uint16_t palette_[16];
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// Lookup tables and state to assist in the IIgs' mapping from NTSC to RGB.
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//
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// My understanding of the real-life algorithm is: maintain a four-bit buffer.
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// Fill it in a circular fashion. Ordinarily, output the result of looking
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// up the RGB mapping of those four bits of Apple II output (which outputs four
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// bits per NTSC colour cycle), commuted as per current phase. But if the bit
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// being inserted differs from that currently in its position in the shift
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// register, hold the existing output for three shifts.
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//
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// From there I am using the following:
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// Maps from the most recent eight bits of Apple II output to how far back
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// into history the graphics system should look for output.
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uint8_t ntsc_shift_lookup_[256];
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int ntsc_shift_ = 0;
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/// Outputs the lowest 14 bits from @c ntsc_shift_, mapping to RGB.
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uint16_t *output_shift(uint16_t *target, int phase) const;
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};
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class Video: public VideoBase {
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public:
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using VideoBase::VideoBase;
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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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