check mode for no change in _mesa_Read/DrawBuffer()

src/mesa/main/buffers.c

-/* $Id: buffers.c,v 1.38 2002/10/04 19:10:07 brianp Exp $ */
+/* $Id: buffers.c,v 1.39 2002/10/11 00:02:16 brianp Exp $ */
 
 /*
  * Mesa 3-D graphics library
    GET_CURRENT_CONTEXT(ctx);
    ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx); /* too complex... */
 
-
    if (MESA_VERBOSE & VERBOSE_API)
       _mesa_debug(ctx, "glDrawBuffer %s\n", _mesa_lookup_enum_by_nr(mode));
 
+   if (ctx->Color.DrawBuffer == mode)
+      return; /* no change */
+
    /*
     * Do error checking and compute the _DrawDestMask bitfield.
     */
    if (MESA_VERBOSE & VERBOSE_API)
       _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(mode));
 
+   if (ctx->Pixel.ReadBuffer == mode)
+      return; /* no change */
+
    switch (mode) {
       case GL_AUX0:
       case GL_AUX1: