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use PRECISION_BITS constant in ImagingAlphaComposite

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use UINT32 instead of UINT16 (a bit faster on x86)
This commit is contained in:
Alexander 2017-09-01 08:37:05 +03:00
parent e6456643d4
commit c59529d28d
1 changed files with 11 additions and 17 deletions
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28
libImaging/AlphaComposite.c
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@ -11,6 +11,7 @@
#include "Imaging.h"
#define PRECISION_BITS 7
typedef struct
{
@ -49,13 +50,11 @@ ImagingAlphaComposite(Imaging imDst, Imaging imSrc)
ImagingCopyInfo(imOut, imDst);
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;
@ -64,25 +63,20 @@ ImagingAlphaComposite(Imaging imDst, Imaging imSrc)
// Each variable has extra meaningful bits.
// Divisions are rounded.
// 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
UINT32 tmpr, tmpg, tmpb;
UINT16 blend = dst->a * (255 - src->a);
UINT16 outa255 = src->a * 255 + blend;
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.
UINT16 coef1 = src->a * 255 * 255 * 128 / outa255;
UINT16 coef2 = 255 * 128 - coef1;
UINT32 coef1 = src->a * 255 * 255 * (1<<PRECISION_BITS) / outa255;
UINT32 coef2 = 255 * (1<<PRECISION_BITS) - coef1;
tmpr = src->r * coef1 + dst->r * coef2 + (0x80 << 7);
out->r = SHIFTFORDIV255(tmpr) >> 7;
tmpg = src->g * coef1 + dst->g * coef2 + (0x80 << 7);
out->g = SHIFTFORDIV255(tmpg) >> 7;
tmpb = src->b * coef1 + dst->b * coef2 + (0x80 << 7);
out->b = SHIFTFORDIV255(tmpb) >> 7;
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);
}