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Precision improvement. ≈60% performance lost

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This commit is contained in:
homm 2013-03-23 14:26:14 +04:00
parent c39a51bcf0
commit e88490b4f2
1 changed files with 13 additions and 16 deletions
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29
libImaging/AlphaComposite.c
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@ -50,35 +50,32 @@ ImagingAlphaComposite(Imaging imDst, Imaging imSrc)
for (y = 0; y < imDst->ysize; y++) {
rgba8* pdst = (rgba8*) imDst->image[y];
rgba8* psrc = (rgba8*) imSrc->image[y];
rgba8* pout = (rgba8*) imOut->image[y];
rgba8* dst = (rgba8*) imDst->image[y];
rgba8* src = (rgba8*) imSrc->image[y];
rgba8* out = (rgba8*) imOut->image[y];
for (x = 0; x < imDst->xsize; x ++) {
rgba8 src = psrc[x];
if (src.a == 0) {
if (src->a == 0) {
// Copy 4 bytes at once.
pout[x] = pdst[x];
*out = *dst;
} else {
rgba8 dst = pdst[x];
rgba8* out = &pout[x];
// Integer implementation with increased precision.
// Each variable has extra meaningful bits.
// Divisions are rounded.
UINT16 blend = dst.a * (255 - src.a); // 16 bit max
UINT16 outa = (src.a << 4) + ((blend + 0x8) >> 4); // 12
UINT16 coef1 = (src.a << 16) / outa; // 12
UINT16 blend = dst->a * (255 - src->a); // 16 bit max
UINT16 outa = (src->a << 4) + ((blend << 4) + 127) / 255; // 12
UINT16 coef1 = ((src->a * 255) << 8) / outa; // 12
UINT16 coef2 = (blend << 8) / outa; // 12
out->r = (src.r * coef1 + dst.r * coef2 + 0x800) >> 12;
out->g = (src.g * coef1 + dst.g * coef2 + 0x800) >> 12;
out->b = (src.b * coef1 + dst.b * coef2 + 0x800) >> 12;
out->a = (outa + 0x8) >> 4;
out->r = ((src->r * coef1 + dst->r * coef2 + 0x7ff) / 255) >> 4;
out->g = ((src->g * coef1 + dst->g * coef2 + 0x7ff) / 255) >> 4;
out->b = ((src->b * coef1 + dst->b * coef2 + 0x7ff) / 255) >> 4;
out->a = (outa + 0x7) >> 4;
}
dst++; src++; out++;
}
}