Add pixel alpha multiply to SDL

FunKey/board/funkey/patches/0001-pixel-alpha-multiply.patch

@@ -0,0 +1,23 @@
+ SDL_blit_A.c |    2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/src/video/SDL_blit_A.c b/src/video/SDL_blit_A.c
+index 219cdcc..d8e921e 100644
+--- a/src/video/SDL_blit_A.c
++++ b/src/video/SDL_blit_A.c
+@@ -2679,6 +2985,7 @@ static void BlitNtoNPixelAlpha(SDL_BlitInfo *info)
+ 	int dstskip = info->d_skip;
+ 	SDL_PixelFormat *srcfmt = info->src;
+ 	SDL_PixelFormat *dstfmt = info->dst;
++	uint8_t alpha_multiply = srcfmt->alpha;
+ 
+ 	int  srcbpp;
+ 	int  dstbpp;
+@@ -2705,6 +3012,7 @@ static void BlitNtoNPixelAlpha(SDL_BlitInfo *info)
+ 		unsigned sA;
+ 		unsigned dA;
+ 		DISEMBLE_RGBA(src, srcbpp, srcfmt, Pixel, sR, sG, sB, sA);
++		sA=(sA*alpha_multiply)>>8;
+ 		if(sA) {
+ 		  DISEMBLE_RGBA(dst, dstbpp, dstfmt, Pixel, dR, dG, dB, dA);
+ 		  ALPHA_BLEND(sR, sG, sB, sA, dR, dG, dB);