util: added util_same_surface() helper function

src/gallium/auxiliary/util/u_surface.h

@@ -37,6 +37,23 @@ struct pipe_texture;
 struct pipe_surface;
 
 
+/**
+ * Are s1 and s2 the same surface?
+ * Surfaces are basically views into textures so check if the two surfaces
+ * name the same part of the same texture.
+ */
+static INLINE boolean
+util_same_surface(const struct pipe_surface *s1, const struct pipe_surface *s2)
+{
+   return (s1->texture == s2->texture &&
+           s1->face == s2->face &&
+           s1->level == s2->level &&
+           s1->zslice == s2->zslice);
+}
+
+
+
+
 extern boolean
 util_create_rgba_surface(struct pipe_screen *screen,
                          uint width, uint height,