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116 lines
3.1 KiB
C++
116 lines
3.1 KiB
C++
//
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// Sprites.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 26/11/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#include "Sprites.hpp"
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using namespace Amiga;
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namespace {
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/// Expands @c source from b15 ... b0 to 000b15 ... 000b0.
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constexpr uint64_t expand_sprite_word(uint16_t source) {
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uint64_t result = source;
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result = (result | (result << 24)) & 0x0000'00ff'0000'00ff;
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result = (result | (result << 12)) & 0x000f'000f'000f'000f;
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result = (result | (result << 6)) & 0x0303'0303'0303'0303;
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result = (result | (result << 3)) & 0x1111'1111'1111'1111;
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return result;
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}
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// A very small selection of test cases.
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static_assert(expand_sprite_word(0xffff) == 0x11'11'11'11'11'11'11'11);
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static_assert(expand_sprite_word(0x5555) == 0x01'01'01'01'01'01'01'01);
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static_assert(expand_sprite_word(0xaaaa) == 0x10'10'10'10'10'10'10'10);
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static_assert(expand_sprite_word(0x0000) == 0x00'00'00'00'00'00'00'00);
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}
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// MARK: - Sprites.
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void Sprite::set_start_position(uint16_t value) {
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v_start_ = (v_start_ & 0xff00) | (value >> 8);
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h_start = uint16_t((h_start & 0x0001) | ((value & 0xff) << 1));
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}
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void Sprite::set_stop_and_control(uint16_t value) {
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h_start = uint16_t((h_start & 0x01fe) | (value & 0x01));
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v_stop_ = uint16_t((value >> 8) | ((value & 0x02) << 7));
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v_start_ = uint16_t((v_start_ & 0x00ff) | ((value & 0x04) << 6));
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attached = value & 0x80;
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// Disarm the sprite, but expect graphics next from DMA.
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visible = false;
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dma_state_ = DMAState::FetchImage;
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}
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void Sprite::set_image_data(int slot, uint16_t value) {
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data[slot] = value;
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visible |= slot == 0;
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}
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void Sprite::advance_line(int y, bool is_end_of_blank) {
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if(dma_state_ == DMAState::FetchImage && y == v_start_) {
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visible = true;
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}
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if(is_end_of_blank || y == v_stop_) {
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dma_state_ = DMAState::FetchControl;
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}
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}
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bool Sprite::advance_dma(int offset) {
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assert(offset == 0 || offset == 1);
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// Determine which word would be fetched, if DMA occurs.
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// A bit of a cheat.
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const uint16_t next_word = ram_[pointer_[0] & ram_mask_];
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// Put the fetched word somewhere appropriate and update the DMA state.
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switch(dma_state_) {
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case DMAState::FetchControl:
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if(offset) {
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set_stop_and_control(next_word);
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} else {
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set_start_position(next_word);
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}
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break;
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case DMAState::FetchImage:
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if(!visible) return false;
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set_image_data(1 - offset, next_word);
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break;
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}
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// Acknowledge the fetch.
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++pointer_[0];
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return true;
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}
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template <int sprite> void TwoSpriteShifter::load(
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uint16_t lsb,
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uint16_t msb,
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int delay) {
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constexpr int sprite_shift = sprite << 1;
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const int delay_shift = delay << 2;
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// Clear out any current sprite pixels; this is a reload.
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data_ &= 0xcccc'cccc'cccc'ccccull >> (sprite_shift + delay_shift);
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// Map LSB and MSB up to 64-bits and load into the shifter.
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const uint64_t new_data =
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(
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expand_sprite_word(lsb) |
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(expand_sprite_word(msb) << 1)
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) << sprite_shift;
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data_ |= new_data >> delay_shift;
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overflow_ |= uint8_t((new_data << 8) >> delay_shift);
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}
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template void TwoSpriteShifter::load<0>(uint16_t, uint16_t, int);
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template void TwoSpriteShifter::load<1>(uint16_t, uint16_t, int);
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