concav(3G)

NAME
     concav - allows the system to draw concave polygons

FORTRAN 77 SPECIFICATION
     subroutine concav(b)
     logical b

PARAMETERS
     b   expects either .TRUE. or .FALSE..

          .TRUE. tells the system to expect concave polygons.

          .FALSE. tells the system to expect no concave polygons. This is the
         default.

DESCRIPTION
     concav tells the system whether or not to expect concave polygons. If you
     try to draw a concave polygon while the system does not expect it, the
     results are unpredictable. Although calling concav(.TRUE.)  guarantees
     that all non-selfintersecting polygons will be drawn correctly, the
     performance of non-concave polygons is reduced on some machines.
     Polygons whose edges intersect each other are never guaranteed to be
     drawn correctly.

     In all cases, performance is optimized when concave polygons are
     decomposed into convex pieces before being passed to a GL drawing
     routine.

SEE ALSO
     bgnpol

BUG
     IRIS-4D GT and GTX models always expect concave polygons, regardless of
     the value of the concav flag.

     On Impact and Infinite Reality concav(.TRUE.)  severely hurts
     performance, and self-intersecting four sided polygons may not render
     correctly.