'Simple windows' represent an easy way to use text input and output in your X-Windows environment The size of a 'simple window' is defined by the calling PROLOG program (' makewindow() '), it can then be used like a normal text terminal screen, using the PROLOG ' readln ()' and ' write ()'predicates. The user can resize the window; Xwio provides scroll bars to change the visible section of the 'simple window'.
Each 'simple window' is identified by its handle, which is returned to the PROLOG process by ' makewindow() '. A PROLOG program can request any number of windows.
The only window always present is ' console ', which is used for system and error messages. A PROLOG process can redirect output here using ' gotowindow() ' with the window handle of 1.
A 'simple window' can only be destroyed by a PROLOG program ( removewindow ), the user can only remove them from the screen by 'hiding' them (or 'minimizing' the size). As Simple Windows are organized like a normal text terminal screen, the position of the next output is defined by a cursor position that Xwio keeps track of. PROLOG applications do not need to place every single output explicitly. The current cursor position can of course be changed by PROLOG (using the ' cursor() ' predicate).