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wrlib: Improvement in the alpha channel support.

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There are some problems in the alpha channel support, as is
reported at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=72917

This patch add a new RCombineAlpha function, based on Gimp. This
function is called when needed in the raster.c functions.

This patch is based on the Brad Jorsch <anomie@users.sourceforge.net>
patch for the 0.62.1-0.1 version.

[crmafra: v1 was sent by Rodolfo kix Garcia <kix@kix.es>]
This commit is contained in:
Christophe CURIS
2012-01-15 20:45:54 +01:00
committed by Carlos R. Mafra
parent e06b3005e8
commit 3ed409cbd0
5 changed files with 142 additions and 92 deletions
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66
wrlib/alpha_combine.c Normal file
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/* alpha_combine.c - Alpha channel combination, based on Gimp 1.1.24
* The GIMP -- an image manipulation program
* Copyright (C) 1995 Spencer Kimball and Peter Mattis
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the Free
* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include "wraster.h"
void RCombineAlpha(unsigned char *d, unsigned char *s, int s_has_alpha,
int width, int height, int dwi, int swi, int opacity) {
int x, y;
int t, sa;
int alpha;
float ratio, cratio;
for (y=0; y<height; y++) {
for (x=0; x<width; x++) {
sa=s_has_alpha?*(s+3):255;
if (opacity!=255) {
t = sa * opacity + 0x80;
sa = ((t>>8)+t)>>8;
}
t = *(d+3) * (255-sa) + 0x80;
alpha = sa + (((t>>8)+t)>>8);
if (sa==0 || alpha==0) {
ratio = 0;
cratio = 1.0;
} else if(sa == alpha) {
ratio = 1.0;
cratio = 0;
} else {
ratio = (float)sa / alpha;
cratio = 1.0 - ratio;
}
*d = (int)*d * cratio + (int)*s * ratio;
s++; d++;
*d = (int)*d * cratio + (int)*s * ratio;
s++; d++;
*d = (int)*d * cratio + (int)*s * ratio;
s++; d++;
*d = alpha;
d++;
if (s_has_alpha) s++;
}
d+=dwi;
s+=swi;
}
}