From b89eada0b9129349e7c32e4d1911c65156ac3c40 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Sat, 6 Dec 2008 05:49:53 +0000
Subject: [PATCH] Fixed SDL_SetAlpha compatibility function to match the
 documentation

---
 src/SDL_compat.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/SDL_compat.c b/src/SDL_compat.c
index e92e7fa0a..925df7a94 100644
--- a/src/SDL_compat.c
+++ b/src/SDL_compat.c
@@ -686,16 +686,19 @@ SDL_GetVideoSurface(void)
 int
 SDL_SetAlpha(SDL_Surface * surface, Uint32 flag, Uint8 value)
 {
-    if (flag & SDL_RLEACCEL) {
-        SDL_SetSurfaceRLE(surface, 1);
-    }
-    if (flag) {
+    if (flag & SDL_SRCALPHA) {
+        /* According to the docs, value is ignored for alpha surfaces */
+        if (surface->format->Amask) {
+            value = 0xFF;
+        }
         SDL_SetSurfaceAlphaMod(surface, value);
         SDL_SetSurfaceBlendMode(surface, SDL_TEXTUREBLENDMODE_BLEND);
     } else {
         SDL_SetSurfaceAlphaMod(surface, 0xFF);
         SDL_SetSurfaceBlendMode(surface, SDL_TEXTUREBLENDMODE_NONE);
     }
+    SDL_SetSurfaceRLE(surface, (flag & SDL_RLEACCEL));
+
     return 0;
 }