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Fix for when VideoMode = {Text_Optimized | TV} in 50% scanline mode:

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. RGB arithmetic could underflow
. Now clamp to zero (ToDo: consider using SIMD)
This commit is contained in:
tomcw 2016-03-27 23:25:28 +01:00
parent 99219a71ec
commit ad55b0f136
1 changed files with 10 additions and 1 deletions
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11
source/NTSC.cpp
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@ -573,7 +573,16 @@ inline void updateFramebufferColorTVSingleScanline( uint16_t signal, bgra_t *pTa
const uint32_t color0 = getScanlineColor( signal, pTable );
const uint32_t color2 = *pLine2Address;
const uint32_t color1 = color0 - ((color2 & 0x00fcfcfc) >> 2); // BUG? color0 - color0? not color0-color2?
// const uint32_t color1 = color0 - ((color2 & 0x00fcfcfc) >> 2); // BUG? color0 - color0? not color0-color2?
// TC: The above operation "color0 - ((color2 & 0x00fcfcfc) >> 2)" causes underflow, so I've recoded to clamp on underflow:
{
int r=(color0>>16)&0xff, g=(color0>>8)&0xff, b=color0&0xff;
uint32_t color2_prime = (color2 & 0x00fcfcfc) >> 2;
r -= (color2_prime>>16)&0xff; if (r<0) r=0; // clamp to 0 on underflow
g -= (color2_prime>>8)&0xff; if (g<0) g=0; // clamp to 0 on underflow
b -= (color2_prime)&0xff; if (b<0) b=0; // clamp to 0 on underflow
const uint32_t color1 = (r<<16)|(g<<8)|(b);
}
/* */ *pLine1Address = color1 | ALPHA32_MASK;
/* */ *pLine0Address = color0;