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annotate src/video/SDL_alphamult.c @ 3474:1edb86163d62

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Of COURSE that trick wouldn't work on all renderers. Fall back to something for now, hopefully figure out a better way to do this later. If we have to, we can use vertical line and horizontal line textures for vertical and horizontal lines, and then create custom textures for diagonal lines and software render those. It's terrible, but at least it would be pixel perfect.
author Sam Lantinga <slouken@libsdl.org>
date Sat, 21 Nov 2009 07:22:59 +0000
parents cd863dd2082b
children f7b03b6838cb
rev   line source
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2009 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: */