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Fix BC3 alpha compression of some constant color blocks showing weird artifacts #9

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Fix BC3 alpha compression of some constant color blocks showing weird artifacts #9

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11 changes: 9 additions & 2 deletions ISPC Texture Compressor/ispc_texcomp/kernel.ispc
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Original file line number Diff line number Diff line change
Expand Up @@ -559,7 +559,15 @@ inline void CompressBlockBC3_alpha(float block[16], uint32 data[2])
ep[1] = max(ep[1], block[k]);
}

if (ep[0] == ep[1]) ep[1] = ep[0]+0.1f;
const int ep0int = clamp((int)ep[0], 0, 255);
const int ep1int = clamp((int)ep[1], 0, 255);
data[0] = ep0int * 256 + ep1int;

if (ep0int == ep1int) // constant color block, so just set all indices to 0
{
data[1] = 0;
return;
}

uint32 qblock[2] = { 0, 0 };
float scale = 7f/(ep[1]-ep[0]);
Expand All @@ -581,7 +589,6 @@ inline void CompressBlockBC3_alpha(float block[16], uint32 data[2])

// (could be improved by refinement)

data[0] = clamp((int)ep[0], 0, 255)*256+clamp((int)ep[1], 0, 255);
data[0] |= qblock[0]<<16;
data[1] = qblock[0]>>16;
data[1] |= qblock[1]<<8;
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