+extern Bool has_writable_cells (Screen *, Visual *);
+extern Visual *id_to_visual (Screen *, int);
+extern int get_bits_per_pixel(Display *dpy, int depth);
+
+extern Visual *get_gl_visual (Screen *);
+extern void describe_gl_visual (FILE *, Screen *, Visual *, Bool priv_cmap_p);
+extern Bool validate_gl_visual (FILE *, Screen *, const char *, Visual *);