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Fix rendering of 'AN3' trick on Apple IIe #32

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Fix rendering of 'AN3' trick on Apple IIe #32

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2 changes: 1 addition & 1 deletion firmware/render/render.c
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Original file line number Diff line number Diff line change
Expand Up @@ -314,7 +314,7 @@ void DELAYED_COPY_CODE(render_loop)()
}
break;
case SOFTSW_HIRES_MODE: //4
if(current_softsw & SOFTSW_DGR)
if((current_softsw & (SOFTSW_80COL | SOFTSW_DGR)) == (SOFTSW_80COL | SOFTSW_DGR))
{
render_dhgr();
}
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12 changes: 9 additions & 3 deletions firmware/render/render_hires.c
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Original file line number Diff line number Diff line change
Expand Up @@ -91,18 +91,24 @@ static void DELAYED_COPY_CODE(render_hires_line)(bool p2, uint line)
// pixel
uint oddness = 0;

// The 'AN3 trick' is used by Prince of Persia and several demos for the IIe.
// It relies on setting AN3 but not turning on 80 column mode. This causes a 90 degree
// phase shift relative to the color carrier which can be used as a quick palette shift
// effect.
uint phase_shift = (IS_SOFTSWITCH(SOFTSW_DGR)) ? 1 : 0;

// Load in the first 14 dots
uint32_t dots = (uint32_t)hires_dot_patterns[line_mem[0]] << 15;
uint32_t dots = (uint32_t)hires_dot_patterns[line_mem[0]] << (15 + phase_shift);

for(uint i=1; i < 41; i++)
{
// Load in the next 14 dots
uint b = (i < 40) ? line_mem[i] : 0;
if(b & 0x80) {
// Extend the last bit from the previous byte
dots |= (dots & (1u << 15)) >> 1;
dots |= (dots & (1u << (15 + phase_shift))) >> 1;
}
dots |= (uint32_t)hires_dot_patterns[b] << 1;
dots |= (uint32_t)hires_dot_patterns[b] << (1 + phase_shift);

// Consume 14 dots
for(uint j=0; j < 7; j++)
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