+ struct drisw_screen *psc = (struct drisw_screen *) pcp->base.psc;
+ struct drisw_drawable *pdraw, *pread;
+
+ pdraw = (struct drisw_drawable *) driFetchDrawable(context, draw);
+ pread = (struct drisw_drawable *) driFetchDrawable(context, read);
+
+ if (pdraw == NULL || pread == NULL)
+ return GLXBadDrawable;