x_screen

     NAME
	  x_screen - part of Simula to Xlib interface

     DESCRIPTION
	     Xlib_Screen class X_Screen(Display, ScreenID,
	     ScreenNumber);
	     ref(Xlib_Display) Display;
	     integer ScreenID;	! Same as XID ;
	     integer ScreenNumber; ! =0,1 or so.;
	  XScreen objects represents the 'glass' screen	of a  display.
	  It  serves as	a mean to get to the HW	characteristics	of the
	  display.  X_Screen is	an abstract superclass with  interface
	  to the Xlib supported	operations. Objects are	created	of the
	  only sub-class have a	few more operations.

	  Objects of  the  sub-class  'XScreen'	 are  created  by  the
	  XDisplay  at	start-up  time,	one for	each available 'glass'
	  screen on the	 display,  often  just	one.  XScreen  objects
	  should  thus	not  be	created	by the application programmer,
	  but the existing one consulted through the  single  XDisplay
	  object.

	  Objects of class 'XVisualInfo' are  returned	as  result  of
	  operation MatchVisualInfo. An	object of class	'XColormap' is
	  an attribute

	  SUPERS: Xlib_Screen, Xlib_Object
	  KIND:	Abstract (only subclass	is XScreen)
	  INIT:	-
	  Sequencing: (<Attributes> / <Query>)*
	  :
	  Attributes=BlackPixel/Cells/DefaultDepth/DefaultVisual/
	  :
	  DisplayOfScreen/DoesBackingStore/DoesSaveUnders/
	  :
	  EventMask/Height/HeightMM/MaxCmaps/MinCmaps/Planes/
	  :		WhitePixel/Width/WidthMM/
	  :	Query=QueryBestCursor/QueryBestStipple/QueryBestTile/
	  :	      MatchVisualInfo

     ATTRIBUTES
     BlackPixel
	     integer BlackPixel;      !	Initialized in XScreen;
	  The black pixel value	in the default colormap

     Cells
	     integer procedure Cells;
	  The number of	colormap cells in the default colormap

     DefaultDepth
	     integer procedure DefaultDepth;
	  The depth (number of	planes)	 of  the  rootwindow  for  the
	  screen

     DefaultVisual
	     integer procedure DefaultVisual;
	  Pointer to the default visual	structure. Magic  number  used
	  how?

     DisplayOfScreen
	     ref(Xlib_Object) procedure	DisplayOfScreen;
	  The display of the screen

     DoesBackingStore
	     integer procedure DoesBackingStore;
	  If the screen	supports backing store

     DoesSaveUnders
	     boolean procedure DoesSaveUnders;
	  If the screen	supports save unders

     EventMask
	     integer procedure EventMask;
	  Initial eventmask for	the rootwindow of the screen

     Height
	     integer procedure Height;
	  Height in pixels of screen

     HeightMM
	     integer procedure HeightMM;
	  Height in mm of screen

     MaxCmaps
	     integer procedure MaxCmaps;
	  Max number of	installed (hardware) colormaps on screen

     MinCmaps
	     integer procedure MinCmaps;
	  Min number of	installed (hardware) colormaps on screen

     Planes
	     integer procedure Planes;
	  The number of	planes in screen

     WhitePixel
	     integer WhitePixel;      !	Initialized in XScreen;
	  The white pixel value	in the default colormap

     Width
	     integer procedure Width;
	  Width	in pixels of screen

     WidthMM
	     integer procedure WidthMM;
	  Width	in mm of screen

     QUERIES
     QueryBestCursor
	     integer procedure QueryBestCursor(Width,Height,
	     WidthReturn,HeightReturn);
	     name WidthReturn, HeightReturn;
	     integer Width, Height, WidthReturn, HeightReturn;
	  Gets the closest supported cursor sizes. The returned	 value
	  to be	used with X_Cursor objects.

     QueryBestStipple
	     integer procedure QueryBestStipple(Width,Height,
	     WidthReturn,HeightReturn);
	     name WidthReturn, HeightReturn;
	     integer Width, Height, WidthReturn, HeightReturn;
	  Obtains the fastest supported	stipple	shape

     QueryBestTile
	     integer procedure QueryBestTile(Width,Height,
	     WidthReturn,HeightReturn);
	     name WidthReturn, HeightReturn;
	     integer Width, Height, WidthReturn, HeightReturn;
	  Obtains the fastest supported	tile shape

     MatchVisualInfo
	     integer procedure
	     MatchVisualInfo(depth,cllass,vinfo_return);
	     name vinfo_return;
	     integer depth,cllass;
	     ref (XVisualInfo) vinfo_return;
	  Obtains the visual  information  that	 matches  the  desired
	  depth	 and  class.  A	 XVisualInfo  object  is  returned  in
	  parameter 'vinfo_return'.