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Merge pull request #156 from homm/master

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Performance improvement of alpha_composite function
This commit is contained in:
Alex Clark ☺ 2013-03-24 12:17:05 -07:00
commit 4554bcb4e4
1 changed files with 53 additions and 52 deletions
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105
libImaging/AlphaComposite.c
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@ -12,81 +12,82 @@
#include "Imaging.h"
typedef struct
{
UINT8 r;
UINT8 g;
UINT8 b;
UINT8 a;
} rgba8;
Imaging
ImagingAlphaComposite(Imaging imDst, Imaging imSrc)
{
Imaging imOut;
int x, y;
float dstR, dstG, dstB, dstA;
float srcR, srcG, srcB, srcA;
float outR, outG, outB, outA;
/* Check arguments */
if (!imDst || !imSrc ||
strcmp(imDst->mode, "RGBA") ||
imDst->type != IMAGING_TYPE_UINT8 ||
imDst->bands != 4)
return ImagingError_ModeError();
strcmp(imDst->mode, "RGBA") ||
imDst->type != IMAGING_TYPE_UINT8 ||
imDst->bands != 4)
return ImagingError_ModeError();
if (strcmp(imDst->mode, imSrc->mode) ||
imDst->type != imSrc->type ||
imDst->bands != imSrc->bands ||
imDst->xsize != imSrc->xsize ||
imDst->ysize != imSrc->ysize)
return ImagingError_Mismatch();
imDst->type != imSrc->type ||
imDst->bands != imSrc->bands ||
imDst->xsize != imSrc->xsize ||
imDst->ysize != imSrc->ysize)
return ImagingError_Mismatch();
imOut = ImagingNew(imDst->mode, imDst->xsize, imDst->ysize);
if (!imOut)
return NULL;
return NULL;
ImagingCopyInfo(imOut, imDst);
for (y = 0; y < imDst->ysize; y++) {
UINT8* dst = (UINT8*) imDst->image[y];
UINT8* src = (UINT8*) imSrc->image[y];
UINT8* out = (UINT8*) 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->linesize; x += 4) {
for (x = 0; x < imDst->xsize; x ++) {
dstR = dst[x + 0] / 255.0;
dstG = dst[x + 1] / 255.0;
dstB = dst[x + 2] / 255.0;
dstA = dst[x + 3] / 255.0;
if (src->a == 0) {
// Copy 4 bytes at once.
*out = *dst;
} else {
// Integer implementation with increased precision.
// Each variable has extra meaningful bits.
// Divisions are rounded.
srcR = src[x + 0] / 255.0;
srcG = src[x + 1] / 255.0;
srcB = src[x + 2] / 255.0;
srcA = src[x + 3] / 255.0;
// This code uses trick from Paste.c:
// (a + (2 << (n-1)) - 1) / ((2 << n)-1)
// almost equivalent to:
// tmp = a + (2 << (n-1)), ((tmp >> n) + tmp) >> n
if (dstA == 1.0) {
outR = srcR * srcA + dstR * (1.0 - srcA);
outG = srcG * srcA + dstG * (1.0 - srcA);
outB = srcB * srcA + dstB * (1.0 - srcA);
outA = 1.0;
} else if (srcA == 0.0) {
outR = dstR;
outG = dstG;
outB = dstB;
outA = dstA;
} else {
outA = srcA + dstA * (1.0 - srcA);
if (outA == 0.0) {
outR = 0.0;
outG = 0.0;
outB = 0.0;
} else {
outR = (srcR * srcA + dstR * dstA * (1.0 - srcA)) / outA;
outG = (srcG * srcA + dstG * dstA * (1.0 - srcA)) / outA;
outB = (srcB * srcA + dstB * dstA * (1.0 - srcA)) / outA;
}
}
// 0xff * 0xff = 16 meaningful bits.
UINT16 blend = dst->a * (255 - src->a);
// Shift 4 bits up, to don't loose blend precision
// on very transparent pixels.
UINT16 outa = (src->a << 4) + (((blend << 4) + (blend >> 4) + 0x80) >> 8);
UINT16 coef1 = (((src->a << 8) - src->a) << 8) / outa; // 12
UINT16 coef2 = (blend << 8) / outa; // 12
out[x + 0] = (UINT8) (255.0 * outR + 0.5);
out[x + 1] = (UINT8) (255.0 * outG + 0.5);
out[x + 2] = (UINT8) (255.0 * outB + 0.5);
out[x + 3] = (UINT8) (255.0 * outA + 0.5);
UINT32 tmpr = src->r * coef1 + dst->r * coef2 + 0x800;
out->r = ((tmpr >> 8) + tmpr) >> 12;
UINT32 tmpg = src->g * coef1 + dst->g * coef2 + 0x800;
out->g = ((tmpg >> 8) + tmpg) >> 12;
UINT32 tmpb = src->b * coef1 + dst->b * coef2 + 0x800;
out->b = ((tmpb >> 8) + tmpb) >> 12;
out->a = (outa + 0x7) >> 4;
}
}
dst++; src++; out++;
}
}