NAME

backface − turns backfacing polygon removal on and off

SPECIFICATION

C
backface(b)
Boolean b;

FORTRAN
subroutine backfa(b)
logical b

Pascal
procedure backface(b: longint);

DESCRIPTION

backface initiates or terminates backfacing polygon removal.  A backfacing polygon is a polygon whose vertices appear in clockwise order in screen space.  When backfacing polygon removal is on, the IRIS displays only polygons whose vertices appear in counterclockwise order. 

The backface utility improves the performance of programs that represent solid objects as collections of polygons.  Because the system determines the orientation of polygons in screen space, backfacing polygon removal does not always remove all hidden surfaces.  When a polygon shrinks to the point where its vertices are coincident, its orientation is indeterminate and it is displayed.  Thus, backfacing polygon removal should be used in conjunction with some other hidden surface removal technique, such as z-buffering. 

SEE ALSO

zbuffer IRIS Graphics Programming, Section 12.2, Backfacing Polygon Removal
 

Version 2.5  —  April 22, 1987