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79a95d7173
To preserve the accuracy of the operation, the C standard request that the mathematical operation is performed using double precision, but in many case this is not necessary so this patch fixes a few constants to avoid that conversion. Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
68 lines
1.8 KiB
C
68 lines
1.8 KiB
C
/* alpha_combine.c - Alpha channel combination, based on Gimp 1.1.24
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* The GIMP -- an image manipulation program
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* Copyright (C) 1995 Spencer Kimball and Peter Mattis
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the Free
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* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
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* MA 02110-1301, USA.
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*/
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#include "wraster.h"
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void RCombineAlpha(unsigned char *d, unsigned char *s, int s_has_alpha,
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int width, int height, int dwi, int swi, int opacity) {
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int x, y;
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int t, sa;
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int alpha;
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float ratio, cratio;
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for (y=0; y<height; y++) {
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for (x=0; x<width; x++) {
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sa=s_has_alpha?*(s+3):255;
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if (opacity!=255) {
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t = sa * opacity + 0x80;
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sa = ((t>>8)+t)>>8;
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}
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t = *(d+3) * (255-sa) + 0x80;
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alpha = sa + (((t>>8)+t)>>8);
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if (sa==0 || alpha==0) {
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ratio = 0;
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cratio = 1.0;
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} else if(sa == alpha) {
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ratio = 1.0;
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cratio = 0;
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} else {
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ratio = (float)sa / alpha;
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cratio = 1.0F - ratio;
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}
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*d = (int)*d * cratio + (int)*s * ratio;
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s++; d++;
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*d = (int)*d * cratio + (int)*s * ratio;
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s++; d++;
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*d = (int)*d * cratio + (int)*s * ratio;
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s++; d++;
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*d = alpha;
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d++;
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if (s_has_alpha) s++;
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}
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d+=dwi;
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s+=swi;
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}
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}
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