DEFINITION MODULE MultiScreen;

	(********************************************************)
	(*							*)
	(*	This module allows the creation of multiple	*)
	(*	virtual screens - complete screens, not just	*)
	(*	windows - with two keyboard "hot keys" used	*)
	(*		to navigate around the screens.		*)
	(*							*)
	(*	We support a two-level hierarchy: a virtual	*)
	(*	screen is a collection of windows, and each	*)
	(*	virtual screen is a member of a group.  (In	*)
	(*	addition, there is a pseudo-group made up of	*)
	(*	all windows which are not associated with	*)
	(*	any virtual screen, to handle the "normal	*)
	(*	output" which bypasses this module.)  One	*)
	(*	hot key cycles through the groups, and the	*)
	(*	second cycles through the virtual screens of	*)
	(*	the currently active group.			*)
	(*							*)
	(*	In the present version, Ctrl/P is the hot	*)
	(*	key used to select another group, and F6	*)
	(*	cycles within a group.				*)
	(*							*)
	(*  Programmer:		P. Moylan			*)
	(*  Last edited:	12 March 1993			*)
	(*  Status:		OK				*)
	(*							*)
	(********************************************************)

FROM Windows IMPORT
    (* type *)	Window, DisplayPage;

TYPE ScreenGroup;	(* is private *)
     VirtualScreen;	(* is private *)

PROCEDURE CreateScreenGroup (hardwarepage: DisplayPage): ScreenGroup;

    (* Creates a new screen group, and maps it to the specified display	*)
    (* page in the screen hardware.  It is permissible to map more than	*)
    (* one group to the same hardware page.  Note that any group on	*)
    (* hardware page 0 shares the screen with "normal output" which	*)
    (* does not belong to any virtual page.  This is permitted, but	*)
    (* on aesthetic grounds is usually not a good idea.			*)

PROCEDURE CreateVirtualScreen (group: ScreenGroup): VirtualScreen;

    (* Adds a new virtual screen to the specified group.	*)

PROCEDURE MapToVirtualScreen (w: Window;  screen: VirtualScreen);

    (* Before calling this procedure, both w and screen must have been	*)
    (* created.  This procedure ensures that window w is visible on	*)
    (* the screen only when the given virtual screen page is active.	*)
    (* The association lasts until the window is closed or the virtual	*)
    (* screen is removed.						*)

PROCEDURE RemoveVirtualScreen (VAR (*INOUT*) screen: VirtualScreen);

    (* Destroys all associations between the given virtual screen and	*)
    (* its windows (but does not close the windows), and permanently	*)
    (* removes this screen from the collection of virtual screens.	*)

PROCEDURE RemoveScreenGroup (VAR (*INOUT*) group: ScreenGroup);

    (* As above, but removes an entire group.	*)

END MultiScreen.