Added a utility function to convert blocks of pixels

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%404172

include/SDL_surface.h

@@ -386,6 +386,15 @@ extern DECLSPEC void SDLCALL SDL_GetClipRect(SDL_Surface * surface,
 extern DECLSPEC SDL_Surface *SDLCALL SDL_ConvertSurface
     (SDL_Surface * src, SDL_PixelFormat * fmt, Uint32 flags);
 
+/**
+ * \brief Copy a block of pixels of one format to another format
+ */
+extern DECLSPEC int SDLCALL SDL_ConvertPixels(int width, int height,
+                                              Uint32 src_format,
+                                              const void * src, int src_pitch,
+                                              Uint32 dst_format,
+                                              void * dst, int dst_pitch);
+
 /**
  *  Draws a point with \c color.
  *