To set the number of user-defined bitplanes you want to use for underlay color or overlay color, call the underlay and overlay subroutines. You cannot use the user-defined bitplanes for overlay and underlay color simultaneously. Call the gconfig subroutine after the overlay or underlay subroutines to activate their settings. List of Underlay and Overlay Mode Subroutines color Sets the current color in color map mode. Chooses a set of bitplanes for drawing.
Overlays are by default enabled for the root window.
Garbage generated by other applications can be left behind in the overlay planes. Since the overlay planes are not automatically cleared when a program terminates, drawings intentionally or unintentionally left behind in the overlay remain visible. The number of acceptable values for n are extremely limited, and depend on the installed adapter. This number can also be queried at run time with the getgdesc subroutine. Although the actual bitplanes are still physically present, their actual contents are no longer visible on the screen.