VErasePanel - erases the panel from the dialog window.
VErasePanel erases the panel from the dialog window. If the panel is
not diaplayed in the dialog window, VErasePanel returns an error code.
VErasePanel erases the panel from the dialog window if the dialog
window is on or from the pixmap if not.
0 - work successfully.
1 - memory allocation error.
216 - the panel is not displayed in the dialog window.
258 - pixmap is null and image window is in front of the dialog window.
VCreateColormap must be called first.