pwlcurve(3G)							  pwlcurve(3G)

NAME    [Toc]    [Back]

     pwlcurve -	describes a piecewise linear trimming curve for	NURBS surfaces

C SPECIFICATION    [Toc]    [Back]

     void pwlcurve(n, data_array, byte_size, type)
     long n, byte_size,	type;
     double *data_array;

PARAMETERS    [Toc]    [Back]

     n		  expects the number of	points on the curve

     data_array	  expects an array containing the curve	points

     byte_size	  expects the offset (in bytes)	between	points on the curve

     type	  expects a value indicating the point type.  Currently, the
		  only data type supported is N_ST, corresponding to pairs of
		  s-t coordinates.  The	offset parameter is used in case the
		  curve	points are part	of an array of larger structure
		  elements. pwlcurve searches for the n-th coordinate pair
		  beginning at data_array + n *	byte_size.

DESCRIPTION    [Toc]    [Back]

     Use pwlcurve to describe a	piecewise linear curve.	 A piecewise linear
     curve consists of a list of pairs of coordinates of points	in the
     parameter space for the NURBS surface.  These points are connected
     together with straight lines to form a path.  If a	piecewise linear curve
     is	an approximation to a real curve, the points should be close enough
     together that the resulting path will appear curved at the	resolution
     used in the application.

     You use piecewise linear curves within trimming loop definitions. A
     trimming loop definition is a set of oriented curve commands that
     describe a	closed loop.  To mark the beginning of a trimming loop
     definition, use the bgntrim command.  To mark the end of a	trimming loop
     definition, use an	endtrim	command.

     You use trimming loop definitions within NURBS surface definitions	(see
     bgnsurface). The trimming loops are closed	curves that the	system uses to
     set the boundaries	of a NURBS surface. You	can describe a trimming	loop
     by	using a	series of piecewise linear curves or NURBS curves (see
     nurbscurve), or both.

     When the system needs to decide which part	of a NURBS surface you want it
     to	display, it displays the region	of the NURBS surface that is to	the
     left of the trimming curves as the	parameter increases. Thus, for a
     counter-clockwise oriented	trimming curve,	the displayed region of	the
     NURBS surface is the region inside	the curve.  For	a clockwise oriented
     trimming curve, the displayed region of the NURBS surface is the region
     outside the curve.





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pwlcurve(3G)							  pwlcurve(3G)



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

SEE ALSO    [Toc]    [Back]

     bgnsurface, nurbssurface, bgntrim,	nurbscurve, getnurbsproperty,
     setnurbsproperty


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