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Issue #2040 - Pre-multiply the alpha values in our JXL decode buffer.

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Using selective calculation (only if not opaque) and fast integer
math here should optimize well in compilers.
This commit is contained in:
Moonchild
2022-11-30 11:32:44 +00:00
committed by roytam1
parent 8b4b6f8ebd
commit 9b4c0ef4e9
1 changed files with 6 additions and 0 deletions
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image/decoders/nsJXLDecoder.cpp
+6
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@@ -145,6 +145,12 @@ nsJXLDecoder::ReadJXLData(const char* aData, size_t aLength)
// We currently have a channel ordering mis-match here.
for (uint8_t* pixPtr = rowPtr; pixPtr < rowPtr + mInfo.xsize * 4; pixPtr+=4){
std::swap(pixPtr[0], pixPtr[2]);
// Pre-multiply, too
if (pixPtr[3] < 255) {
pixPtr[0]=((uint16_t)pixPtr[0]*(uint16_t)pixPtr[3]) >> 8;
pixPtr[1]=((uint16_t)pixPtr[1]*(uint16_t)pixPtr[3]) >> 8;
pixPtr[2]=((uint16_t)pixPtr[2]*(uint16_t)pixPtr[3]) >> 8;
}
}
pipe->WriteBuffer(reinterpret_cast<uint32_t*>(rowPtr));
}