bgnsurface(3G)							bgnsurface(3G)

NAME    [Toc]    [Back]

     bgnsurface, endsurface - delimit a	NURBS surface definition

C SPECIFICATION    [Toc]    [Back]

     void bgnsurface()

     void endsurface()

PARAMETERS    [Toc]    [Back]

     none

DESCRIPTION    [Toc]    [Back]

     Use bgnsurface to mark the	beginning of a NURBS (Non-Uniform Rational BSpline)
 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    [Toc]    [Back]

     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();



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bgnsurface(3G)							bgnsurface(3G)

NOTE    [Toc]    [Back]

     On	Impact and Infinite Reality lmcolor cannot be called between
     bgnsurface	and endsurface

SEE ALSO    [Toc]    [Back]

     nurbssurface, bgntrim, nurbscurve,	pwlcurve, setnurbsproperty,
     getnurbsproperty


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