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comparison src/video/SDL_alphamult.c @ 3054:8d93bfecb9dc

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Fixed alpha blending textures with the GDI renderer
author Sam Lantinga <slouken@libsdl.org>
date Sat, 07 Feb 2009 17:56:08 +0000
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children cd863dd2082b
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3053:aa34d1180d30 3054:8d93bfecb9dc
1 /*
2 SDL - Simple DirectMedia Layer
3 Copyright (C) 1997-2009 Sam Lantinga
4
5 This library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 This library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with this library; if not, write to the Free Software
17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
18
19 Sam Lantinga
20 slouken@libsdl.org
21 */
22 #include "SDL_config.h"
23
24 #include "SDL_blit.h"
25 #include "SDL_alphamult.h"
26
27 /* Functions to pre-multiply the alpha channel into the color channels */
28
29 #define DEFINE_PREMULTIPLY_FUNC(fmt) \
30 void \
31 SDL_PreMultiplyAlpha##fmt(int w, int h, Uint32 *pixels, int pitch) \
32 { \
33 pitch /= 4; \
34 while (h--) { \
35 int n; \
36 Uint32 *row = pixels; \
37 Uint32 pixel; \
38 unsigned r, g, b, a; \
39 \
40 for (n = w; n--; ) { \
41 pixel = *row; \
42 RGBA_FROM_##fmt(pixel, r, g, b, a); \
43 r = (r * a) / 255; \
44 g = (g * a) / 255; \
45 b = (b * a) / 255; \
46 fmt##_FROM_RGBA(*row, r, g, b, a); \
47 ++row; \
48 } \
49 pixels += pitch; \
50 } \
51 }
52
53 DEFINE_PREMULTIPLY_FUNC(ARGB8888)
54 DEFINE_PREMULTIPLY_FUNC(RGBA8888)
55 DEFINE_PREMULTIPLY_FUNC(ABGR8888)
56 DEFINE_PREMULTIPLY_FUNC(BGRA8888)
57
58 /* vi: set ts=4 sw=4 expandtab: */