Split SDL_BlitScaled into SDL_UpperBlitScaled and SDL_LowerBlitScaled.

Fixed issue when calling SDL_BlitScaled() directly with src or dst rectangles that were out of bounds.

include/SDL_surface.h

@@ -466,15 +466,23 @@ extern DECLSPEC int SDLCALL SDL_SoftStretch(SDL_Surface * src,
                                             SDL_Surface * dst,
                                             const SDL_Rect * dstrect);
 
+#define SDL_BlitScaled SDL_UpperBlitScaled
+
 /**
- *  \brief Perform a fast, low quality, stretch blit between two surfaces of the
- *         different pixel formats.
- *  
- *  \note This function calls SDL_SoftStretch or SDL_LowerBlit.
+ *  This is the public scaled blit function, SDL_BlitScaled(), and it performs
+ *  rectangle validation and clipping before passing it to SDL_LowerBlitScaled()
  */
-extern DECLSPEC int SDLCALL SDL_BlitScaled
+extern DECLSPEC int SDLCALL SDL_UpperBlitScaled
     (SDL_Surface * src, const SDL_Rect * srcrect,
-    SDL_Surface * dst, const SDL_Rect * dstrect);
+    SDL_Surface * dst, SDL_Rect * dstrect);
+
+/**
+ *  This is a semi-private blit function and it performs low-level surface
+ *  scaled blitting only.
+ */
+extern DECLSPEC int SDLCALL SDL_LowerBlitScaled
+    (SDL_Surface * src, SDL_Rect * srcrect,
+    SDL_Surface * dst, SDL_Rect * dstrect);
 
 
 /* Ends C function definitions when using C++ */