nurbssurface(3G)					      nurbssurface(3G)

NAME    [Toc]    [Back]

     nurbssurface - controls the shape of a NURBS surface

C SPECIFICATION    [Toc]    [Back]

     void nurbssurface(s_knot_count, s_knot, t_knot_count, t_knot,
		       s_offset, t_offset, ctlarray,
		       s_order,	t_order, type)
     long s_knot_count,	t_knot_count;
     double s_knot[], t_knot[];
     long s_offset, t_offset;
     double *ctlarray;
     long s_order, t_order, type;

PARAMETERS    [Toc]    [Back]

     s_knot_count   expects the	number of knots	in the parametric s direction.

     s_knot	    expects an array of	s_knot_count non-decreasing knot
		    values in the parametric s direction.

     t_knot_count   expects the	number of knots	in the parametric t direction.

     t_knot	    expects an array of	t_knot_count non-decreasing knot
		    values in the parametric t direction.

     s_offset	    expects the	offset (in bytes) between successive control
		    points in the parametric s direction in ctlarray.

     t_offset	    expects the	offset (in bytes) between successive control
		    points in the parametric t direction in ctlarray.

     ctlarray	    expects an array containing	control	points for the NURBS
		    surface.  The coordinates must appear as either (x,	y, z)
		    triples or as (wx, wy, wz, w) quadruples.  The offsets
		    between successive control points in the parametric	s and
		    t directions are given by s_offset and t_offset.

     s_order	    expects the	order of the NURBS surface in the parametric s
		    direction.	The order is one more than the degree, hence,
		    a cubic surface has	an order of 4.

     t_order	    expects the	order of the NURBS surface in the parametric t
		    direction.	The order is one more than the degree, hence,
		    a cubic surface has	an order of 4.

     type	    expects a value indicating the control point type.
		    Current options are	N_V3D, N_V3DR, N_C4D, N_C4DR, and
		    N_T2D, N_T2DR.  Types N_V3D	and N_V3DR denote doubleprecision
 positional coordinates in	a three-dimensional
		    model space.  N_V3D	denotes	non-rational (3) coordinates
		    and	N_V3DR denotes rational	(4) coordinates.  Types	N_C4D
		    and	N_C4DR denote double-precision color coordinates in a
		    four-dimensional RGBA color	space.	N_C4D denotes non


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nurbssurface(3G)					      nurbssurface(3G)



		    rational coordinates and N_C4DR denotes rational
		    coordinates.  Types	N_T2D and N_T2DR denote	doubleprecision
 texture coordinates in a two-dimensional texture
		    space.  N_T2D denotes non-rational coordinates and N_T2DR
		    denotes rational coordinates.

DESCRIPTION    [Toc]    [Back]

     Use the nurbssurface command within a NURBS (Non-Uniform Rational BSpline)
 surface definition	to describe the	shape of a NURBS surface
     before any	trimming takes place.  To mark the beginning of	a NURBS
     surface definition, use the bgnsurface command.  To mark the end of a
     NURBS surface definition, use the endsurface command.  Call nurbssurface
     within a NURBS surface definition only.

     Positional, texture, and color coordinates	are associated by presenting
     each as a separate	nurbssurface between a bgnsurface/endsurface pair.  No
     more than one call	to nurbssurface	for each of color and texture data may
     be	made within a single bgnsurface/endsurface pair.  Exactly one call
     must be made to describe position data and	it must	be the last call to
     nurbssurface between the bracketing bgnsurface/endsurface.

EXAMPLE    [Toc]    [Back]

	  bgnsurface();
	      nurbssurface( ..., N_C4D );   /* color data */
	      nurbssurface( ..., N_T2D );   /* texture data */
	      nurbssurface( ..., N_V3D );   /* position	data */
	  endsurface();


     You can trim a NURBS surface by using the commands	nurbscurve and
     pwlcurve between calls to bgntrim and endtrim.

     Observe that a nurbssurface with s_knot_count knots in the	s direction
     and t_knot_count knots in the t direction with orders s_order and t_order
     must have (s_knot_count - s_order)	x (t_knot_count	- t_order) control
     points.

     The system	renders	a NURBS	surface	as a polygonal mesh and	analytically
     calculates	normal vectors at the corners of the polygons within the mesh.
     Therefore,	your code should specify a lighting model when it uses NURBS
     surfaces. Otherwise, you loose all	the interesting	surface	information.
     Use lmdef and lmbind to define or modify materials	and their properties.

     See the Graphics Library Programming Guide	for a mathematical description
     of	a NURBS	surface.

SEE ALSO    [Toc]    [Back]

     bgnsurface, nurbscurve, bgntrim, pwlcurve,	getnurbsproperty,
     setnurbsproperty, texbind






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nurbssurface(3G)					      nurbssurface(3G)

NOTE    [Toc]    [Back]

     nurbssurface commands specifying color or texture coordinates currently
     have no effect on IRIS-4D G, GT, GTX, and Personal	IRIS.


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