[MPlayer-cvslog] r28223 - trunk/spudec.c

[reimar]

Author: reimar
Date: Thu Jan  1 12:33:46 2009
New Revision: 28223

Log:
Simplify and comment spudec bilinear scaling code

Modified:
   trunk/spudec.c

Modified: trunk/spudec.c
==============================================================================
--- trunk/spudec.c	Thu Jan  1 12:23:32 2009	(r28222)
+++ trunk/spudec.c	Thu Jan  1 12:33:46 2009	(r28223)
@@ -737,9 +737,10 @@ static void scale_image(int x, int y, sc
   spu->scaled_image[scaled] = (color[0] * scale[0] + color[1] * scale[1] + color[2] * scale[2] + color[3] * scale[3])>>24;
   spu->scaled_aimage[scaled] = (scale[0] + scale[1] + scale[2] + scale[3]) >> 16;
   if (spu->scaled_aimage[scaled]){
-    spu->scaled_aimage[scaled] = 256 - spu->scaled_aimage[scaled];
-    if(spu->scaled_aimage[scaled] + spu->scaled_image[scaled] > 255)
-      spu->scaled_image[scaled] = 256 - spu->scaled_aimage[scaled];
+    // ensure that MPlayer's simplified alpha-blending can not overflow
+    spu->scaled_image[scaled] = FFMIN(spu->scaled_image[scaled], spu->scaled_aimage[scaled]);
+    // convert to MPlayer-style alpha
+    spu->scaled_aimage[scaled] = -spu->scaled_aimage[scaled];
   }
 }