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annotate src/video/SDL_alphamult.c @ 4504:9faebccfefb3

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Amazingly the Windows code is almost identical to the Mac OS X code. :)
author Sam Lantinga <slouken@libsdl.org>
date Thu, 08 Jul 2010 23:07:34 -0700
parents f7b03b6838cb
children
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2010 Sam Lantinga
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4
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5 This library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Lesser General Public
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7 License as published by the Free Software Foundation; either
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8 version 2.1 of the License, or (at your option) any later version.
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9
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10 This library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Lesser General Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser General Public
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16 License along with this library; if not, write to the Free Software
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17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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18
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19 Sam Lantinga
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20 slouken@libsdl.org
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21 */
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22 #include "SDL_config.h"
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23
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24 #include "SDL_blit.h"
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25 #include "SDL_alphamult.h"
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26
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27 /* Functions to pre-multiply the alpha channel into the color channels */
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28
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29 #define DEFINE_PREMULTIPLY_FUNC(fmt) \
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30 void \
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31 SDL_PreMultiplyAlpha##fmt(int w, int h, Uint32 *pixels, int pitch) \
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32 { \
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33 pitch /= 4; \
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34 while (h--) { \
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35 int n; \
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36 Uint32 *row = pixels; \
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37 Uint32 pixel; \
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38 unsigned r, g, b, a; \
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39 \
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40 for (n = w; n--; ) { \
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41 pixel = *row; \
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42 RGBA_FROM_##fmt(pixel, r, g, b, a); \
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43 r = (r * a) / 255; \
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44 g = (g * a) / 255; \
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45 b = (b * a) / 255; \
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46 fmt##_FROM_RGBA(*row, r, g, b, a); \
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47 ++row; \
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48 } \
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49 pixels += pitch; \
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50 } \
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51 }
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52
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53 /* *INDENT-OFF* */
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54 DEFINE_PREMULTIPLY_FUNC(ARGB8888)
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55 DEFINE_PREMULTIPLY_FUNC(RGBA8888)
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56 DEFINE_PREMULTIPLY_FUNC(ABGR8888)
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57 DEFINE_PREMULTIPLY_FUNC(BGRA8888)
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58 /* *INDENT-ON* */
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59
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60 /* vi: set ts=4 sw=4 expandtab: */