endsurface(3G)

NAME
     bgnsurface, endsurface - delimit a NURBS surface definition

C SPECIFICATION
     void bgnsurface()

     void endsurface()

PARAMETERS
     none

DESCRIPTION
     Use bgnsurface to mark the beginning of a NURBS (Non-Uniform Rational B-
     Spline) surface definition. After you call bgnsurface, call the routines
     that define the surface and that provide the trimming information.  To
     mark the end of a NURBS surface definition, call endsurface.

     Within a NURBS surface definition (between bgnsurface and endsurface) you
     may use only the following Graphics Library subroutines:  nurbssurface,
     bgntrim, endtrim, nurbscurve, and pwlcurve.  The NURBS surface definition
     must consist of exactly one call to nurbssurface to define the shape of
     the surface.  In addition, this call may be preceeded by calls to
     nurbssurface that specify how texture and color parameters vary across
     the surface.  The call(s) to nurbssurface may be followed by a list of
     one or more trimming loop definitions (to define the boundaries of the
     surface).  Each trimming loop definition consists of one call to bgntrim,
     one or more calls to either pwlcurve or nurbscurve, and one call to
     endtrim.

     The system renders a NURBS surface as a polygonal mesh, and calculates
     normal vectors at the corners of the polygons within the mesh. Therefore,
     your program should specify a lighting model if it uses NURBS surfaces.
     If your program uses no lighting model, all the interesting surface
     information is lost.  When using a lighting model, use lmdef and lmbind
     to define or modify materials and their properties.

EXAMPLE
     The following code fragment draws a NURBS surface trimmed by two closed
     loops.  The first closed loop is a single piecewise linear curve (see
     pwlcurve), and the second closed loop consists of two NURBS curves (see
     nurbscurve) joined end to end:

          bgnsurface();
              nurbssurface(. . .);
              bgntrim();
                  pwlcurve(. . .);
              endtrim();
              bgntrim();
                  nurbscurve(. . .);
                  nurbscurve(. . .);
              endtrim();
          endsurface();
NOTE
     On Impact and Infinite Reality lmcolor cannot be called between
     bgnsurface and endsurface


SEE ALSO
     nurbssurface, bgntrim, nurbscurve, pwlcurve, setnurbsproperty,
     getnurbsproperty