pwlcurve(3G)

NAME
     pwlcurve - describes a piecewise linear trimming curve for NURBS surfaces

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

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

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