mirror of
https://github.com/python-pillow/Pillow.git
synced 2024-12-28 02:46:18 +03:00
91 lines
2.5 KiB
C
91 lines
2.5 KiB
C
/*
|
|
* The Python Imaging Library
|
|
* $Id$
|
|
*
|
|
* Alpha composite imSrc over imDst.
|
|
* https://en.wikipedia.org/wiki/Alpha_compositing
|
|
*
|
|
* See the README file for details on usage and redistribution.
|
|
*/
|
|
|
|
|
|
#include "Imaging.h"
|
|
|
|
#define PRECISION_BITS 7
|
|
|
|
typedef struct
|
|
{
|
|
UINT8 r;
|
|
UINT8 g;
|
|
UINT8 b;
|
|
UINT8 a;
|
|
} rgba8;
|
|
|
|
|
|
|
|
Imaging
|
|
ImagingAlphaComposite(Imaging imDst, Imaging imSrc)
|
|
{
|
|
Imaging imOut;
|
|
int x, y;
|
|
|
|
/* Check arguments */
|
|
if (!imDst || !imSrc ||
|
|
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();
|
|
}
|
|
|
|
imOut = ImagingNewDirty(imDst->mode, imDst->xsize, imDst->ysize);
|
|
if (!imOut) {
|
|
return NULL;
|
|
}
|
|
|
|
for (y = 0; y < imDst->ysize; 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 ++) {
|
|
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.
|
|
|
|
UINT32 tmpr, tmpg, tmpb;
|
|
UINT32 blend = dst->a * (255 - src->a);
|
|
UINT32 outa255 = src->a * 255 + blend;
|
|
// There we use 7 bits for precision.
|
|
// We could use more, but we go beyond 32 bits.
|
|
UINT32 coef1 = src->a * 255 * 255 * (1<<PRECISION_BITS) / outa255;
|
|
UINT32 coef2 = 255 * (1<<PRECISION_BITS) - coef1;
|
|
|
|
tmpr = src->r * coef1 + dst->r * coef2;
|
|
tmpg = src->g * coef1 + dst->g * coef2;
|
|
tmpb = src->b * coef1 + dst->b * coef2;
|
|
out->r = SHIFTFORDIV255(tmpr + (0x80<<PRECISION_BITS)) >> PRECISION_BITS;
|
|
out->g = SHIFTFORDIV255(tmpg + (0x80<<PRECISION_BITS)) >> PRECISION_BITS;
|
|
out->b = SHIFTFORDIV255(tmpb + (0x80<<PRECISION_BITS)) >> PRECISION_BITS;
|
|
out->a = SHIFTFORDIV255(outa255 + 0x80);
|
|
}
|
|
|
|
dst++; src++; out++;
|
|
}
|
|
|
|
}
|
|
|
|
return imOut;
|
|
}
|