frontface(3G)

NAME
     frontface - turns frontfacing polygon removal on and off

C SPECIFICATION
     void frontface(b)
     Boolean b;

PARAMETERS
     b   expects either TRUE or FALSE.

         TRUE suppresses the display of frontfacing filled polygons.

         FALSE allows the display of frontfacing filled polygons.

DESCRIPTION
     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
     backface, zbuffer

NOTE
     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.