Futurebasic/Language/Reference/window fill

Syntax
WINDOW FILL [[#]expr

Description
This statement immediately redraws, in the current output window, any controls, edit fields and picture fields which intersect with the window's "invalid region." The window's invalid region consists of those visible parts of the window which were recently uncovered but haven't yet been refreshed; you can also add an arbitrary rectangle to the invalid region using the new (in Release 6).

After redrawing the controls etc.,  resets the window's invalid region to a nil (empty) region. This will inhibit FB from generating a event for the window the next time   is executed.If no window number is used for , FB assumes that you wish to use the current output window.

Note
You will rarely need to use this statement. FB automatically redraws controls, edit fields and picture fields as necessary every time your program executes.