From: Gabriel Gambetta To: SDL Mailing List <sdl@libsdl.org> Date: Fri, 17 Nov 2006 00:39:29 -0200 Subject: [SDL] Alpha blending bug - fixed? It turns out mm5 never got the correct value. This failed : [...] "movd %1, %%mm5\n\t" : : "m" (amask), "m" (sf->Ashift) ); mm5 got 0xFF000018 instead of 0x00000018. However I did this : Uint32 ashift = sf->Ashift; [...] "movd %1, %%mm5\n\t" : : "m" (amask), "m" (ashift) ); and everything worked fine. The only thing I could find out was that ashift is 32-bit aligned but sf->Ashift isn't: printf("ashift %8X [%d]\n", &ashift, (int)(&ashift) % 4); printf("sf->Ashift %8X [%d]\n", &sf->Ashift, (int)(&sf->Ashift) % 4); ashift at BFF0E0C4 [0] sf->Ashift at 08AFB9CD [1] Could this be the problem? If it is, the fix is extremely trivial. Should I submit a patch? --Gabriel

--- a/src/video/SDL_blit_A.c	Tue Nov 21 20:49:35 2006 +0000
+++ b/src/video/SDL_blit_A.c	Tue Nov 21 23:17:00 2006 +0000
@@ -1566,6 +1566,7 @@
 	int dstskip = info->d_skip >> 2;
 	SDL_PixelFormat* sf = info->src;
 	Uint32 amask = sf->Amask;
+	Uint32 ashift = sf->Ashift;
 
 	__asm__ (
 	/* make mm6 all zeros. */
@@ -1587,7 +1588,7 @@
 	/* get alpha channel shift */
 	"movd      %1, %%mm5\n\t" /* Ashift -> mm5 */
 
-	  : /* nothing */ : "m" (sf->Amask), "m" (sf->Ashift) );
+	  : /* nothing */ : "m" (amask), "m" (ashift) );
 
 	while(height--) {