--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/video/SDL_alphamult.c	Sat Feb 07 17:56:08 2009 +0000
@@ -0,0 +1,58 @@
+/*
+    SDL - Simple DirectMedia Layer
+    Copyright (C) 1997-2009 Sam Lantinga
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Lesser General Public
+    License as published by the Free Software Foundation; either
+    version 2.1 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
+    Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public
+    License along with this library; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+    Sam Lantinga
+    slouken@libsdl.org
+*/
+#include "SDL_config.h"
+
+#include "SDL_blit.h"
+#include "SDL_alphamult.h"
+
+/* Functions to pre-multiply the alpha channel into the color channels */
+
+#define DEFINE_PREMULTIPLY_FUNC(fmt) \
+void \
+SDL_PreMultiplyAlpha##fmt(int w, int h, Uint32 *pixels, int pitch) \
+{ \
+    pitch /= 4; \
+    while (h--) { \
+        int n; \
+        Uint32 *row = pixels; \
+        Uint32 pixel; \
+        unsigned r, g, b, a; \
+ \
+        for (n = w; n--; ) { \
+            pixel = *row; \
+            RGBA_FROM_##fmt(pixel, r, g, b, a); \
+            r = (r * a) / 255; \
+            g = (g * a) / 255; \
+            b = (b * a) / 255; \
+            fmt##_FROM_RGBA(*row, r, g, b, a); \
+            ++row; \
+        } \
+        pixels += pitch; \
+    } \
+}
+
+DEFINE_PREMULTIPLY_FUNC(ARGB8888)
+DEFINE_PREMULTIPLY_FUNC(RGBA8888)
+DEFINE_PREMULTIPLY_FUNC(ABGR8888)
+DEFINE_PREMULTIPLY_FUNC(BGRA8888)
+
+/* vi: set ts=4 sw=4 expandtab: */