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70 lines
2.2 KiB
C
70 lines
2.2 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, see
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* <https://www.gnu.org/licenses/>.
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*/
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#include "config.h"
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#include "wraster.h"
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#include "wr_i18n.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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unsigned char *dst = d;
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unsigned char *src = s;
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for (y = 0; y < height; y++) {
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for (x = 0; x < width; x++) {
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int sa = s_has_alpha ? src[3] : 255;
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int t, alpha;
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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 = dst[3] * (255 - sa) + 0x80;
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alpha = sa + (((t >> 8) + t) >> 8);
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if (alpha == 0) {
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dst[3] = 0;
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} else if (sa == alpha) {
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dst[0] = src[0];
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dst[1] = src[1];
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dst[2] = src[2];
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dst[3] = alpha;
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} else if (sa == 0) {
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dst[3] = alpha;
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} else {
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int ratio = (sa << 8) / alpha;
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int inv_ratio = 256 - ratio;
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dst[0] = (dst[0] * inv_ratio + src[0] * ratio) >> 8;
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dst[1] = (dst[1] * inv_ratio + src[1] * ratio) >> 8;
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dst[2] = (dst[2] * inv_ratio + src[2] * ratio) >> 8;
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dst[3] = alpha;
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}
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dst += 4;
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src += s_has_alpha ? 4 : 3;
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}
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dst += dwi;
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src += swi;
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}
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} |