frontface(3G)							 frontface(3G)

NAME    [Toc]    [Back]

     frontface - turns frontfacing polygon removal on and off

C SPECIFICATION    [Toc]    [Back]

     void frontface(b)
     Boolean b;

PARAMETERS    [Toc]    [Back]

     b	 expects either	TRUE or	FALSE.

	 TRUE suppresses the display of	frontfacing filled polygons.

	 FALSE allows the display of frontfacing filled	polygons.

DESCRIPTION    [Toc]    [Back]

     frontface allows or suppresses the	display	of frontfacing filled
     polygons.	If your	programs represent solid objects as collections	of
     polygons, you can use this	routine	to expose hidden surfaces.    This
     routine works best	for simple convex objects that do not obscure other
     objects.

     A frontfacing polygon is defined as a polygon whose vertices are in
     counter-clockwise order in	screen coordinates.  When frontfacing polygon
     removal is	on, the	system displays	only polygons whose vertices are in
     clockwise order.  For complicated objects,	this routine alone may not
     expose all	hidden surfaces. To expose hidden surfaces for more
     complicated objects or groups of objects, your routine needs to check the
     relative distances	of the object from the viewer (z values).  (See
     ``Hidden Surface Removal''	in the Graphics	Library	Programming Guide.)

     If	frontface and backface are asserted simultaneously, no filled polygons
     will be displayed.

SEE ALSO    [Toc]    [Back]

     backface, zbuffer

NOTE    [Toc]    [Back]

     On	IRIS-4D	G and B	models frontface does not work well when a polygon
     shrinks to	the point where	its vertices are coincident.  Under these
     conditions, the routine cannot determine the orientation of the polygon
     and so displays the polygon by default.

     On	all IRIS-4D models matrices that negate	coordinates, such as scale (-
     1.0, 1.0, 1.0), reverse the directional order of a	polygon's points and
     can cause frontface to do the opposite of what is intended.


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