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713 lines
24 KiB
C++
713 lines
24 KiB
C++
//
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// 9918.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 25/11/2017.
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// Copyright © 2017 Thomas Harte. All rights reserved.
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//
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#include "9918.hpp"
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#include <cassert>
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#include <cstring>
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using namespace TI;
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namespace {
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const uint32_t palette_pack(uint8_t r, uint8_t g, uint8_t b) {
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uint32_t result = 0;
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uint8_t *const result_ptr = reinterpret_cast<uint8_t *>(&result);
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result_ptr[0] = r;
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result_ptr[1] = g;
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result_ptr[2] = b;
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result_ptr[3] = 0;
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return result;
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}
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const uint32_t palette[16] = {
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palette_pack(0, 0, 0),
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palette_pack(0, 0, 0),
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palette_pack(33, 200, 66),
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palette_pack(94, 220, 120),
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palette_pack(84, 85, 237),
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palette_pack(125, 118, 252),
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palette_pack(212, 82, 77),
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palette_pack(66, 235, 245),
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palette_pack(252, 85, 84),
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palette_pack(255, 121, 120),
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palette_pack(212, 193, 84),
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palette_pack(230, 206, 128),
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palette_pack(33, 176, 59),
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palette_pack(201, 91, 186),
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palette_pack(204, 204, 204),
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palette_pack(255, 255, 255)
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};
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const uint8_t StatusInterrupt = 0x80;
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const uint8_t StatusFifthSprite = 0x40;
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const int StatusSpriteCollisionShift = 5;
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const uint8_t StatusSpriteCollision = 0x20;
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struct ReverseTable {
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std::uint8_t map[256];
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ReverseTable() {
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for(int c = 0; c < 256; ++c) {
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map[c] = static_cast<uint8_t>(
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((c & 0x80) >> 7) |
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((c & 0x40) >> 5) |
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((c & 0x20) >> 3) |
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((c & 0x10) >> 1) |
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((c & 0x08) << 1) |
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((c & 0x04) << 3) |
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((c & 0x02) << 5) |
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((c & 0x01) << 7)
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);
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}
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}
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} reverse_table;
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// Bits are reversed in the internal mode value; they're stored
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// in the order M1 M2 M3. Hence the definitions below.
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enum ScreenMode {
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Text = 4,
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MultiColour = 2,
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ColouredText = 0,
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Graphics = 1
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};
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}
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TMS9918Base::TMS9918Base() :
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// 342 internal cycles are 228/227.5ths of a line, so 341.25 cycles should be a whole
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// line. Therefore multiply everything by four, but set line length to 1365 rather than 342*4 = 1368.
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crt_(new Outputs::CRT::CRT(1365, 4, Outputs::CRT::DisplayType::NTSC60, 4)) {}
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TMS9918::TMS9918(Personality p) {
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// Unimaginatively, this class just passes RGB through to the shader. Investigation is needed
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// into whether there's a more natural form.
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crt_->set_rgb_sampling_function(
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"vec3 rgb_sample(usampler2D sampler, vec2 coordinate, vec2 icoordinate)"
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"{"
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"return texture(sampler, coordinate).rgb / vec3(255.0);"
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"}");
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crt_->set_output_device(Outputs::CRT::OutputDevice::Monitor);
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crt_->set_visible_area(Outputs::CRT::Rect(0.055f, 0.025f, 0.9f, 0.9f));
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crt_->set_input_gamma(2.8f);
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// The TMS remains in-phase with the NTSC colour clock; this is an empirical measurement
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// intended to produce the correct relationship between the hard edges between pixels and
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// the colour clock. It was eyeballed rather than derived from any knowledge of the TMS
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// colour burst generator because I've yet to find any.
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crt_->set_immediate_default_phase(0.85f);
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}
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Outputs::CRT::CRT *TMS9918::get_crt() {
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return crt_.get();
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}
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void TMS9918Base::test_sprite(int sprite_number, int screen_row) {
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if(!(status_ & StatusFifthSprite)) {
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status_ = static_cast<uint8_t>((status_ & ~31) | sprite_number);
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}
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if(sprites_stopped_)
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return;
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const int sprite_position = ram_[sprite_attribute_table_address_ + (sprite_number << 2)];
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// A sprite Y of 208 means "don't scan the list any further".
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if(sprite_position == 208) {
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sprites_stopped_ = true;
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return;
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}
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const int sprite_row = (screen_row - sprite_position)&255;
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if(sprite_row < 0 || sprite_row >= sprite_height_) return;
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const int active_sprite_slot = sprite_sets_[active_sprite_set_].active_sprite_slot;
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if(active_sprite_slot == 4) {
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status_ |= StatusFifthSprite;
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return;
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}
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SpriteSet::ActiveSprite &sprite = sprite_sets_[active_sprite_set_].active_sprites[active_sprite_slot];
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sprite.index = sprite_number;
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sprite.row = sprite_row >> (sprites_magnified_ ? 1 : 0);
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sprite_sets_[active_sprite_set_].active_sprite_slot++;
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}
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void TMS9918Base::get_sprite_contents(int field, int cycles_left, int screen_row) {
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int sprite_id = field / 6;
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field %= 6;
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while(true) {
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const int cycles_in_sprite = std::min(cycles_left, 6 - field);
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cycles_left -= cycles_in_sprite;
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const int final_field = cycles_in_sprite + field;
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assert(sprite_id < 4);
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SpriteSet::ActiveSprite &sprite = sprite_sets_[active_sprite_set_].active_sprites[sprite_id];
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if(field < 4) {
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std::memcpy(
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&sprite.info[field],
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&ram_[sprite_attribute_table_address_ + (sprite.index << 2) + field],
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static_cast<size_t>(std::min(4, final_field) - field));
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}
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field = std::min(4, final_field);
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const int sprite_offset = sprite.info[2] & ~(sprites_16x16_ ? 3 : 0);
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const int sprite_address = sprite_generator_table_address_ + (sprite_offset << 3) + sprite.row; // TODO: recalclate sprite.row from screen_row (?)
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while(field < final_field) {
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sprite.image[field - 4] = ram_[sprite_address + ((field - 4) << 4)];
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field++;
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}
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if(!cycles_left) return;
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field = 0;
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sprite_id++;
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}
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}
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void TMS9918::run_for(const HalfCycles cycles) {
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// As specific as I've been able to get:
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// Scanline time is always 228 cycles.
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// PAL output is 313 lines total. NTSC output is 262 lines total.
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// Interrupt is signalled upon entering the lower border.
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// Keep a count of cycles separate from internal counts to avoid
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// potential errors mapping back and forth.
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half_cycles_into_frame_ = (half_cycles_into_frame_ + cycles) % HalfCycles(frame_lines_ * 228 * 2);
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// Convert 456 clocked half cycles per line to 342 internal cycles per line;
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// the internal clock is 1.5 times the nominal 3.579545 Mhz that I've advertised
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// for this part. So multiply by three quarters.
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int int_cycles = (cycles.as_int() * 3) + cycles_error_;
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cycles_error_ = int_cycles & 3;
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int_cycles >>= 2;
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if(!int_cycles) return;
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while(int_cycles) {
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// Determine how much time has passed in the remainder of this line, and proceed.
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int cycles_left = std::min(342 - column_, int_cycles);
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// ------------------------------------
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// Potentially perform a memory access.
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// ------------------------------------
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if(queued_access_ != MemoryAccess::None) {
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int time_until_access_slot = 0;
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switch(line_mode_) {
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case LineMode::Refresh:
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if(column_ < 53 || column_ >= 307) time_until_access_slot = column_&1;
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else time_until_access_slot = 3 - ((column_ - 53)&3);
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// i.e. 53 -> 3, 52 -> 2, 51 -> 1, 50 -> 0, etc
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break;
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case LineMode::Text:
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if(column_ < 59 || column_ >= 299) time_until_access_slot = column_&1;
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else time_until_access_slot = 5 - ((column_ + 3)%6);
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// i.e. 59 -> 3, 60 -> 2, 61 -> 1, etc
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break;
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case LineMode::Character:
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if(column_ < 9) time_until_access_slot = column_&1;
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else if(column_ < 30) time_until_access_slot = 30 - column_;
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else if(column_ < 37) time_until_access_slot = column_&1;
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else if(column_ < 311) time_until_access_slot = 31 - ((column_ + 7)&31);
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// i.e. 53 -> 3, 54 -> 2, 55 -> 1, 56 -> 0, 57 -> 31, etc
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else if(column_ < 313) time_until_access_slot = column_&1;
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else time_until_access_slot = 342 - column_;
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break;
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}
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if(cycles_left >= time_until_access_slot) {
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if(queued_access_ == MemoryAccess::Write) {
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ram_[ram_pointer_ & 16383] = read_ahead_buffer_;
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} else {
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read_ahead_buffer_ = ram_[ram_pointer_ & 16383];
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}
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ram_pointer_++;
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queued_access_ = MemoryAccess::None;
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}
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}
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column_ += cycles_left; // column_ is now the column that has been reached in this line.
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int_cycles -= cycles_left; // Count down duration to run for.
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// ------------------------------
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// Perform video memory accesses.
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// ------------------------------
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if(((row_ < 192) || (row_ == frame_lines_-1)) && !blank_screen_) {
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const int sprite_row = (row_ < 192) ? row_ : -1;
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const int access_slot = column_ >> 1; // There are only 171 available memory accesses per line.
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switch(line_mode_) {
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default: break;
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case LineMode::Text:
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access_pointer_ = std::min(30, access_slot);
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if(access_pointer_ >= 30 && access_pointer_ < 150) {
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const int row_base = pattern_name_address_ + (row_ >> 3) * 40;
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const int end = std::min(150, access_slot);
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// Pattern names are collected every third window starting from window 30.
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const int pattern_names_start = (access_pointer_ - 30 + 2) / 3;
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const int pattern_names_end = (end - 30 + 2) / 3;
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std::memcpy(&pattern_names_[pattern_names_start], &ram_[row_base + pattern_names_start], static_cast<size_t>(pattern_names_end - pattern_names_start));
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// Patterns are collected every third window starting from window 32.
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const int pattern_buffer_start = (access_pointer_ - 32 + 2) / 3;
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const int pattern_buffer_end = (end - 32 + 2) / 3;
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for(int column = pattern_buffer_start; column < pattern_buffer_end; ++column) {
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pattern_buffer_[column] = ram_[pattern_generator_table_address_ + (pattern_names_[column] << 3) + (row_ & 7)];
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}
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}
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break;
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case LineMode::Character:
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// Four access windows: no collection.
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if(access_pointer_ < 5)
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access_pointer_ = std::min(5, access_slot);
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// Then ten access windows are filled with collection of sprite 3 and 4 details.
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if(access_pointer_ >= 5 && access_pointer_ < 15) {
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int end = std::min(15, access_slot);
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get_sprite_contents(access_pointer_ - 5 + 14, end - access_pointer_, sprite_row - 1);
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access_pointer_ = std::min(15, access_slot);
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}
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// Four more access windows: no collection.
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if(access_pointer_ >= 15 && access_pointer_ < 19) {
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access_pointer_ = std::min(19, access_slot);
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// Start new sprite set if this is location 19.
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if(access_pointer_ == 19) {
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active_sprite_set_ ^= 1;
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sprite_sets_[active_sprite_set_].active_sprite_slot = 0;
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sprites_stopped_ = false;
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}
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}
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// Then eight access windows fetch the y position for the first eight sprites.
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while(access_pointer_ < 27 && access_pointer_ < access_slot) {
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test_sprite(access_pointer_ - 19, sprite_row);
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access_pointer_++;
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}
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// The next 128 access slots are video and sprite collection interleaved.
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if(access_pointer_ >= 27 && access_pointer_ < 155) {
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int end = std::min(155, access_slot);
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int row_base = pattern_name_address_;
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int pattern_base = pattern_generator_table_address_;
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int colour_base = colour_table_address_;
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if(screen_mode_ == ScreenMode::Graphics) {
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// If this is high resolution mode, allow the row number to affect the pattern and colour addresses.
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pattern_base &= 0x2000 | ((row_ & 0xc0) << 5);
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colour_base &= 0x2000 | ((row_ & 0xc0) << 5);
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}
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row_base += (row_ << 2)&~31;
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// Pattern names are collected every fourth window starting from window 27.
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const int pattern_names_start = (access_pointer_ - 27 + 3) >> 2;
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const int pattern_names_end = (end - 27 + 3) >> 2;
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std::memcpy(&pattern_names_[pattern_names_start], &ram_[row_base + pattern_names_start], static_cast<size_t>(pattern_names_end - pattern_names_start));
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// Colours are collected every fourth window starting from window 29.
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const int colours_start = (access_pointer_ - 29 + 3) >> 2;
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const int colours_end = (end - 29 + 3) >> 2;
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if(screen_mode_ != 1) {
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for(int column = colours_start; column < colours_end; ++column) {
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colour_buffer_[column] = ram_[colour_base + (pattern_names_[column] >> 3)];
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}
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} else {
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for(int column = colours_start; column < colours_end; ++column) {
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colour_buffer_[column] = ram_[colour_base + (pattern_names_[column] << 3) + (row_ & 7)];
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}
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}
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// Patterns are collected ever fourth window starting from window 30.
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const int pattern_buffer_start = (access_pointer_ - 30 + 3) >> 2;
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const int pattern_buffer_end = (end - 30 + 3) >> 2;
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// Multicolour mode uss a different function of row to pick bytes
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const int row = (screen_mode_ != 2) ? (row_ & 7) : ((row_ >> 2) & 7);
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for(int column = pattern_buffer_start; column < pattern_buffer_end; ++column) {
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pattern_buffer_[column] = ram_[pattern_base + (pattern_names_[column] << 3) + row];
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}
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// Sprite slots occur in three quarters of ever fourth window starting from window 28.
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const int sprite_start = (access_pointer_ - 28 + 3) >> 2;
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const int sprite_end = (end - 28 + 3) >> 2;
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for(int column = sprite_start; column < sprite_end; ++column) {
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if(column&3) {
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test_sprite(7 + column - (column >> 2), sprite_row);
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}
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}
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access_pointer_ = std::min(155, access_slot);
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}
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// Two access windows: no collection.
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if(access_pointer_ < 157)
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access_pointer_ = std::min(157, access_slot);
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// Fourteen access windows: collect initial sprite information.
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if(access_pointer_ >= 157 && access_pointer_ < 171) {
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int end = std::min(171, access_slot);
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get_sprite_contents(access_pointer_ - 157, end - access_pointer_, sprite_row);
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access_pointer_ = std::min(171, access_slot);
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}
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break;
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}
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}
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// --------------------------
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// End video memory accesses.
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// --------------------------
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// --------------------
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// Output video stream.
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// --------------------
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if(row_ < 192 && !blank_screen_) {
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// ----------------------
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// Output horizontal sync
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// ----------------------
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if(!output_column_ && column_ >= 26) {
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crt_->output_sync(13 * 4);
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crt_->output_default_colour_burst(13 * 4);
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output_column_ = 26;
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}
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// -------------------
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// Output left border.
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// -------------------
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if(output_column_ >= 26) {
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int pixels_end = std::min(first_pixel_column_, column_);
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if(output_column_ < pixels_end) {
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output_border(pixels_end - output_column_);
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output_column_ = pixels_end;
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// Grab a pointer for drawing pixels to, if the moment has arrived.
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if(pixels_end == first_pixel_column_) {
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pixel_base_ = pixel_target_ = reinterpret_cast<uint32_t *>(crt_->allocate_write_area(static_cast<unsigned int>(first_right_border_column_ - first_pixel_column_)));
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}
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}
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}
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// --------------
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// Output pixels.
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// --------------
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if(output_column_ >= first_pixel_column_) {
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int pixels_end = std::min(first_right_border_column_, column_);
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if(output_column_ < pixels_end) {
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switch(line_mode_) {
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default: break;
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case LineMode::Text: {
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const uint32_t colours[2] = { palette[background_colour_], palette[text_colour_] };
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const int shift = (output_column_ - first_pixel_column_) % 6;
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int byte_column = (output_column_ - first_pixel_column_) / 6;
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int pattern = reverse_table.map[pattern_buffer_[byte_column]] >> shift;
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int pixels_left = pixels_end - output_column_;
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int length = std::min(pixels_left, 6 - shift);
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while(true) {
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pixels_left -= length;
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for(int c = 0; c < length; ++c) {
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pixel_target_[c] = colours[pattern&0x01];
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pattern >>= 1;
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}
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pixel_target_ += length;
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if(!pixels_left) break;
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length = std::min(6, pixels_left);
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byte_column++;
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pattern = reverse_table.map[pattern_buffer_[byte_column]];
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}
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output_column_ = pixels_end;
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} break;
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case LineMode::Character: {
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// If this is the start of the visible area, seed sprite shifter positions.
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SpriteSet &sprite_set = sprite_sets_[active_sprite_set_ ^ 1];
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if(output_column_ == first_pixel_column_) {
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int c = sprite_set.active_sprite_slot;
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while(c--) {
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SpriteSet::ActiveSprite &sprite = sprite_set.active_sprites[c];
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sprite.shift_position = -sprite.info[1];
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if(sprite.info[3] & 0x80) {
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sprite.shift_position += 32;
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if(sprite.shift_position > 0 && !sprites_magnified_)
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sprite.shift_position *= 2;
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}
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}
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}
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// Paint the background tiles.
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const int pixels_left = pixels_end - output_column_;
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if(screen_mode_ == ScreenMode::MultiColour) {
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int pixel_location = output_column_ - first_pixel_column_;
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for(int c = 0; c < pixels_left; ++c) {
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pixel_target_[c] = palette[
|
|
(pattern_buffer_[(pixel_location + c) >> 3] >> (((pixel_location + c) & 4)^4)) & 15
|
|
];
|
|
}
|
|
pixel_target_ += pixels_left;
|
|
} else {
|
|
const int shift = (output_column_ - first_pixel_column_) & 7;
|
|
int byte_column = (output_column_ - first_pixel_column_) >> 3;
|
|
|
|
int length = std::min(pixels_left, 8 - shift);
|
|
|
|
int pattern = reverse_table.map[pattern_buffer_[byte_column]] >> shift;
|
|
uint8_t colour = colour_buffer_[byte_column];
|
|
uint32_t colours[2] = {
|
|
palette[(colour & 15) ? (colour & 15) : background_colour_],
|
|
palette[(colour >> 4) ? (colour >> 4) : background_colour_]
|
|
};
|
|
|
|
int background_pixels_left = pixels_left;
|
|
while(true) {
|
|
background_pixels_left -= length;
|
|
for(int c = 0; c < length; ++c) {
|
|
pixel_target_[c] = colours[pattern&0x01];
|
|
pattern >>= 1;
|
|
}
|
|
pixel_target_ += length;
|
|
|
|
if(!background_pixels_left) break;
|
|
length = std::min(8, background_pixels_left);
|
|
byte_column++;
|
|
|
|
pattern = reverse_table.map[pattern_buffer_[byte_column]];
|
|
colour = colour_buffer_[byte_column];
|
|
colours[0] = palette[(colour & 15) ? (colour & 15) : background_colour_];
|
|
colours[1] = palette[(colour >> 4) ? (colour >> 4) : background_colour_];
|
|
}
|
|
}
|
|
|
|
// Paint sprites and check for collisions.
|
|
if(sprite_set.active_sprite_slot) {
|
|
int sprite_pixels_left = pixels_left;
|
|
const int shift_advance = sprites_magnified_ ? 1 : 2;
|
|
|
|
const uint32_t sprite_colour_selection_masks[2] = {0x00000000, 0xffffffff};
|
|
const int colour_masks[16] = {0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
|
|
|
|
while(sprite_pixels_left--) {
|
|
uint32_t sprite_colour = pixel_base_[output_column_ - first_pixel_column_];
|
|
int sprite_mask = 0;
|
|
int c = sprite_set.active_sprite_slot;
|
|
while(c--) {
|
|
SpriteSet::ActiveSprite &sprite = sprite_set.active_sprites[c];
|
|
|
|
if(sprite.shift_position < 0) {
|
|
sprite.shift_position++;
|
|
continue;
|
|
} else if(sprite.shift_position < 32) {
|
|
int mask = sprite.image[sprite.shift_position >> 4] << ((sprite.shift_position&15) >> 1);
|
|
mask = (mask >> 7) & 1;
|
|
status_ |= (mask & sprite_mask) << StatusSpriteCollisionShift;
|
|
sprite_mask |= mask;
|
|
sprite.shift_position += shift_advance;
|
|
|
|
mask &= colour_masks[sprite.info[3]&15];
|
|
sprite_colour = (sprite_colour & sprite_colour_selection_masks[mask^1]) | (palette[sprite.info[3]&15] & sprite_colour_selection_masks[mask]);
|
|
}
|
|
}
|
|
|
|
pixel_base_[output_column_ - first_pixel_column_] = sprite_colour;
|
|
output_column_++;
|
|
}
|
|
}
|
|
|
|
output_column_ = pixels_end;
|
|
} break;
|
|
}
|
|
|
|
if(output_column_ == first_right_border_column_) {
|
|
crt_->output_data(static_cast<unsigned int>(first_right_border_column_ - first_pixel_column_) * 4, 4);
|
|
pixel_target_ = nullptr;
|
|
}
|
|
}
|
|
}
|
|
|
|
// --------------------
|
|
// Output right border.
|
|
// --------------------
|
|
if(output_column_ >= first_right_border_column_) {
|
|
output_border(column_ - output_column_);
|
|
output_column_ = column_;
|
|
}
|
|
} else if(row_ >= first_vsync_line_ && row_ < first_vsync_line_+3) {
|
|
// Vertical sync.
|
|
if(column_ == 342) {
|
|
crt_->output_sync(342 * 4);
|
|
}
|
|
} else {
|
|
// Blank.
|
|
if(!output_column_ && column_ >= 26) {
|
|
crt_->output_sync(13 * 4);
|
|
crt_->output_default_colour_burst(13 * 4);
|
|
output_column_ = 26;
|
|
}
|
|
if(output_column_ >= 26) {
|
|
output_border(column_ - output_column_);
|
|
output_column_ = column_;
|
|
}
|
|
}
|
|
// -----------------
|
|
// End video stream.
|
|
// -----------------
|
|
|
|
|
|
|
|
// -----------------------------------
|
|
// Prepare for next line, potentially.
|
|
// -----------------------------------
|
|
if(column_ == 342) {
|
|
access_pointer_ = column_ = output_column_ = 0;
|
|
row_ = (row_ + 1) % frame_lines_;
|
|
if(row_ == 192) status_ |= StatusInterrupt;
|
|
|
|
screen_mode_ = next_screen_mode_;
|
|
blank_screen_ = next_blank_screen_;
|
|
switch(screen_mode_) {
|
|
case ScreenMode::Text:
|
|
line_mode_ = LineMode::Text;
|
|
first_pixel_column_ = 69;
|
|
first_right_border_column_ = 309;
|
|
break;
|
|
default:
|
|
line_mode_ = LineMode::Character;
|
|
first_pixel_column_ = 63;
|
|
first_right_border_column_ = 319;
|
|
break;
|
|
}
|
|
if(blank_screen_ || (row_ >= 192 && row_ != frame_lines_-1)) line_mode_ = LineMode::Refresh;
|
|
}
|
|
}
|
|
}
|
|
|
|
void TMS9918Base::output_border(int cycles) {
|
|
pixel_target_ = reinterpret_cast<uint32_t *>(crt_->allocate_write_area(1));
|
|
if(pixel_target_) *pixel_target_ = palette[background_colour_];
|
|
crt_->output_level(static_cast<unsigned int>(cycles) * 4);
|
|
}
|
|
|
|
void TMS9918::set_register(int address, uint8_t value) {
|
|
// Writes to address 0 are writes to the video RAM. Store
|
|
// the value and return.
|
|
if(!(address & 1)) {
|
|
write_phase_ = false;
|
|
|
|
// Enqueue the write to occur at the next available slot.
|
|
read_ahead_buffer_ = value;
|
|
queued_access_ = MemoryAccess::Write;
|
|
|
|
return;
|
|
}
|
|
|
|
// Writes to address 1 are performed in pairs; if this is the
|
|
// low byte of a value, store it and wait for the high byte.
|
|
if(!write_phase_) {
|
|
low_write_ = value;
|
|
write_phase_ = true;
|
|
return;
|
|
}
|
|
|
|
write_phase_ = false;
|
|
if(value & 0x80) {
|
|
// This is a write to a register.
|
|
switch(value & 7) {
|
|
case 0:
|
|
next_screen_mode_ = (next_screen_mode_ & 6) | ((low_write_ & 2) >> 1);
|
|
break;
|
|
|
|
case 1:
|
|
next_blank_screen_ = !(low_write_ & 0x40);
|
|
generate_interrupts_ = !!(low_write_ & 0x20);
|
|
next_screen_mode_ = (next_screen_mode_ & 1) | ((low_write_ & 0x18) >> 2);
|
|
sprites_16x16_ = !!(low_write_ & 0x02);
|
|
sprites_magnified_ = !!(low_write_ & 0x01);
|
|
|
|
sprite_height_ = 8;
|
|
if(sprites_16x16_) sprite_height_ <<= 1;
|
|
if(sprites_magnified_) sprite_height_ <<= 1;
|
|
break;
|
|
|
|
case 2:
|
|
pattern_name_address_ = static_cast<uint16_t>((low_write_ & 0xf) << 10);
|
|
break;
|
|
|
|
case 3:
|
|
colour_table_address_ = static_cast<uint16_t>(low_write_ << 6);
|
|
break;
|
|
|
|
case 4:
|
|
pattern_generator_table_address_ = static_cast<uint16_t>((low_write_ & 0x07) << 11);
|
|
break;
|
|
|
|
case 5:
|
|
sprite_attribute_table_address_ = static_cast<uint16_t>((low_write_ & 0x7f) << 7);
|
|
break;
|
|
|
|
case 6:
|
|
sprite_generator_table_address_ = static_cast<uint16_t>((low_write_ & 0x07) << 11);
|
|
break;
|
|
|
|
case 7:
|
|
text_colour_ = low_write_ >> 4;
|
|
background_colour_ = low_write_ & 0xf;
|
|
break;
|
|
}
|
|
} else {
|
|
// This is a write to the RAM pointer.
|
|
ram_pointer_ = static_cast<uint16_t>(low_write_ | (value << 8));
|
|
if(!(value & 0x40)) {
|
|
// Officially a 'read' set, so perform lookahead.
|
|
queued_access_ = MemoryAccess::Read;
|
|
}
|
|
}
|
|
}
|
|
|
|
uint8_t TMS9918::get_register(int address) {
|
|
write_phase_ = false;
|
|
|
|
// Reads from address 0 read video RAM, via the read-ahead buffer.
|
|
if(!(address & 1)) {
|
|
// Enqueue the write to occur at the next available slot.
|
|
uint8_t result = read_ahead_buffer_;
|
|
queued_access_ = MemoryAccess::Read;
|
|
return result;
|
|
}
|
|
|
|
// Reads from address 1 get the status register.
|
|
uint8_t result = status_;
|
|
status_ &= ~(StatusInterrupt | StatusFifthSprite | StatusSpriteCollision);
|
|
return result;
|
|
}
|
|
|
|
HalfCycles TMS9918::get_time_until_interrupt() {
|
|
if(!generate_interrupts_) return HalfCycles(-1);
|
|
if(get_interrupt_line()) return HalfCycles(0);
|
|
|
|
const int half_cycles_per_frame = frame_lines_ * 228 * 2;
|
|
int half_cycles_remaining = (192 * 228 * 2 + half_cycles_per_frame - half_cycles_into_frame_.as_int()) % half_cycles_per_frame;
|
|
return HalfCycles(half_cycles_remaining ? half_cycles_remaining : half_cycles_per_frame);
|
|
}
|
|
|
|
bool TMS9918::get_interrupt_line() {
|
|
return (status_ & StatusInterrupt) && generate_interrupts_;
|
|
}
|