Change SDL_BLENDMODE_MUL for gl renderers

 Add FIXME for PSP and DirectFB

src/render/SDL_render.c

@@ -87,7 +87,7 @@ this should probably be removed at some point in the future.  --ryan. */
 
 #define SDL_BLENDMODE_MUL_FULL                                                                                    \
     SDL_COMPOSE_BLENDMODE(SDL_BLENDFACTOR_DST_COLOR, SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA, SDL_BLENDOPERATION_ADD, \
-                          SDL_BLENDFACTOR_DST_ALPHA, SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA, SDL_BLENDOPERATION_ADD)
+                          SDL_BLENDFACTOR_ZERO, SDL_BLENDFACTOR_ONE, SDL_BLENDOPERATION_ADD)
 
 #if !SDL_RENDER_DISABLED
 static const SDL_RenderDriver *render_drivers[] = {

src/render/psp/SDL_render_psp.c

@@ -993,6 +993,7 @@ static void PSP_SetBlendState(PSP_RenderData *data, PSP_BlendState *state)
             break;
         case SDL_BLENDMODE_MUL:
             sceGuTexFunc(GU_TFX_MODULATE, GU_TCC_RGBA);
+            /* FIXME SDL_BLENDMODE_MUL is simplified, and dstA is in fact un-changed.*/
             sceGuBlendFunc(GU_ADD, GU_DST_COLOR, GU_ONE_MINUS_SRC_ALPHA, 0, 0);
             sceGuEnable(GU_BLEND);
             break;

src/video/directfb/SDL_DirectFB_render.c

@@ -201,6 +201,7 @@ SetBlendMode(DirectFB_RenderData * data, int blendMode,
         case SDL_BLENDMODE_MUL:
             data->blitFlags = DSBLIT_BLEND_ALPHACHANNEL;
             data->drawFlags = DSDRAW_BLEND;
+            /* FIXME SDL_BLENDMODE_MUL is simplified, and dstA is in fact un-changed.*/
             SDL_DFB_CHECK(destsurf->SetSrcBlendFunction(destsurf, DSBF_DESTCOLOR));
             SDL_DFB_CHECK(destsurf->SetDstBlendFunction(destsurf, DSBF_INVSRCALPHA));