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CLK/Machines/Apple/AppleIIgs/Video.hpp

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//
// Video.hpp
// Clock Signal
//
// Created by Thomas Harte on 31/10/2020.
// Copyright © 2020 Thomas Harte. All rights reserved.
//
#pragma once
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#include "../AppleII/VideoSwitches.hpp"
#include "../../../Outputs/CRT/CRT.hpp"
#include "../../../ClockReceiver/ClockReceiver.hpp"
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namespace Apple::IIgs::Video {
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/*!
Provides IIgs video output; assumed clocking here is seven times the usual Apple II clock.
So it'll produce a single line of video every 456 cycles 65*7 + 1, allowing for the
stretched cycle.
*/
class Video: public Apple::II::VideoSwitches<Cycles> {
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public:
Video();
void set_internal_ram(const uint8_t *);
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bool get_is_vertical_blank(Cycles offset);
uint8_t get_horizontal_counter(Cycles offset);
uint8_t get_vertical_counter(Cycles offset);
void set_new_video(uint8_t);
uint8_t get_new_video();
void clear_interrupts(uint8_t);
uint8_t get_interrupt_register();
void set_interrupt_register(uint8_t);
bool get_interrupt_line();
void notify_clock_tick();
void set_border_colour(uint8_t);
void set_text_colour(uint8_t);
uint8_t get_text_colour();
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uint8_t get_border_colour();
void set_composite_is_colour(bool);
bool get_composite_is_colour();
/// Sets the scan target.
void set_scan_target(Outputs::Display::ScanTarget *scan_target);
/// Gets the current scan status.
Outputs::Display::ScanStatus get_scaled_scan_status() const;
/// Sets the type of output.
void set_display_type(Outputs::Display::DisplayType);
/// Gets the type of output.
Outputs::Display::DisplayType get_display_type() const;
/// Determines the period until video might autonomously update its interrupt lines.
Cycles next_sequence_point() const;
/// Sets the Mega II interrupt enable state — 1/4-second and VBL interrupts are
/// generated here.
void set_megaii_interrupts_enabled(uint8_t);
uint8_t get_megaii_interrupt_status();
void clear_megaii_interrupts();
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private:
Outputs::CRT::CRT crt_;
// This is coupled to Apple::II::GraphicsMode, but adds detail for the IIgs.
enum class GraphicsMode {
Text = 0,
DoubleText,
HighRes,
DoubleHighRes,
LowRes,
DoubleLowRes,
FatLowRes,
// Additions:
DoubleHighResMono,
SuperHighRes
};
constexpr bool is_colour_ntsc(GraphicsMode m) { return m >= GraphicsMode::HighRes && m <= GraphicsMode::FatLowRes; }
GraphicsMode graphics_mode(int row) const {
if(new_video_ & 0x80) {
return GraphicsMode::SuperHighRes;
}
const auto ii_mode = Apple::II::VideoSwitches<Cycles>::graphics_mode(row);
switch(ii_mode) {
// Coupling very much assumed here.
case Apple::II::GraphicsMode::DoubleHighRes:
if(new_video_ & 0x20) {
return GraphicsMode::DoubleHighResMono;
}
[[fallthrough]];
default: return GraphicsMode(int(ii_mode)); break;
}
}
enum class PixelBufferFormat {
Text, DoubleText, NTSC, NTSCMono, SuperHighRes
};
constexpr PixelBufferFormat format_for_mode(GraphicsMode m) {
switch(m) {
case GraphicsMode::Text: return PixelBufferFormat::Text;
case GraphicsMode::DoubleText: return PixelBufferFormat::DoubleText;
default: return PixelBufferFormat::NTSC;
case GraphicsMode::DoubleHighResMono: return PixelBufferFormat::NTSCMono;
case GraphicsMode::SuperHighRes: return PixelBufferFormat::SuperHighRes;
}
}
void advance(Cycles);
uint8_t new_video_ = 0x01;
class Interrupts {
public:
void add(uint8_t value) {
// Taken literally, status accumulates regardless of being enabled,
// potentially to be polled, it simply doesn't trigger an interrupt.
value_ |= value;
test();
}
void clear(uint8_t value) {
// Zeroes in bits 5 or 6 clear the respective interrupts.
value_ &= value | ~0x60;
test();
}
void set_control(uint8_t value) {
// Ones in bits 1 or 2 enable the respective interrupts.
value_ = (value_ & ~0x6) | (value & 0x6);
test();
}
uint8_t status() const {
return value_;
}
bool active() const {
return value_ & 0x80;
}
private:
void test() {
value_ &= 0x7f;
if((value_ >> 4) & value_ & 0x6) {
value_ |= 0x80;
}
}
// Overall meaning of value is as per the VGC interrupt register, i.e.
//
// b7: interrupt status;
// b6: 1-second interrupt status;
// b5: scan-line interrupt status;
// b4: reserved;
// b3: reserved;
// b2: 1-second interrupt enable;
// b1: scan-line interrupt enable;
// b0: reserved.
uint8_t value_ = 0x00;
} interrupts_;
int cycles_into_frame_ = 0;
const uint8_t *ram_ = nullptr;
// The modal colours.
uint16_t border_colour_ = 0;
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uint8_t border_colour_entry_ = 0;
uint8_t text_colour_entry_ = 0xf0;
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uint16_t text_colour_ = 0xffff;
uint16_t background_colour_ = 0;
// Current pixel output buffer and conceptual format.
PixelBufferFormat pixels_format_;
uint16_t *pixels_ = nullptr, *next_pixel_ = nullptr;
int pixels_start_column_;
void output_row(int row, int start, int end);
uint16_t *output_super_high_res(uint16_t *target, int start, int end, int row) const;
uint16_t *output_text(uint16_t *target, int start, int end, int row) const;
uint16_t *output_double_text(uint16_t *target, int start, int end, int row) const;
uint16_t *output_char(uint16_t *target, uint8_t source, int row) const;
uint16_t *output_low_resolution(uint16_t *target, int start, int end, int row);
uint16_t *output_fat_low_resolution(uint16_t *target, int start, int end, int row);
uint16_t *output_double_low_resolution(uint16_t *target, int start, int end, int row);
uint16_t *output_high_resolution(uint16_t *target, int start, int end, int row);
uint16_t *output_double_high_resolution(uint16_t *target, int start, int end, int row);
uint16_t *output_double_high_resolution_mono(uint16_t *target, int start, int end, int row);
// Super high-res per-line state.
uint8_t line_control_;
uint16_t palette_[16];
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// Storage used for fill mode.
uint16_t *palette_zero_[4] = {nullptr, nullptr, nullptr, nullptr}, palette_throwaway_;
// Lookup tables and state to assist in the IIgs' mapping from NTSC to RGB.
//
// My understanding of the real-life algorithm is: maintain a four-bit buffer.
// Fill it in a circular fashion. Ordinarily, output the result of looking
// up the RGB mapping of those four bits of Apple II output (which outputs four
// bits per NTSC colour cycle), commuted as per current phase. But if the bit
// being inserted differs from that currently in its position in the shift
// register, hold the existing output for three shifts.
//
// From there I am using the following:
// Maps from:
//
// b0 = b0 of the shift register
// b1 = b4 of the shift register
// b2 = current delay count
//
// to a new delay count.
uint8_t ntsc_delay_lookup_[20];
uint32_t ntsc_shift_ = 0; // Assumption here: logical shifts will ensue, rather than arithmetic.
int ntsc_delay_ = 0;
/// Outputs the lowest 14 bits from @c ntsc_shift_, mapping to RGB.
/// Phase is derived from @c column.
uint16_t *output_shift(uint16_t *target, int column);
// Common getter for the two counters.
struct Counters {
Counters(int v, int h) : vertical(v), horizontal(h) {}
const int vertical, horizontal;
};
Counters get_counters(Cycles offset);
// Marshalls the Mega II-style interrupt state.
uint8_t megaii_interrupt_mask_ = 0;
uint8_t megaii_interrupt_state_ = 0;
int megaii_frame_counter_ = 0; // To count up to quarter-second interrupts.
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};
}