Describes a piecewise linear trimming curve for NURBS surfaces.

FORTRAN (**libfgl.a**)

void pwlcurve(Int32count,Float64*data_array,Int32stride,Int32type)

SUBROUTINE PWLCUR(count,data_array,stride,type)INTEGER*4count,stride,typeREAL*8data_array(*)

The **pwlcurve **subroutine describes a piecewise linear curve, which consists of a list of coordinate pairs in the parameter space for a Non-Uniform Rational B-Spline (NURBS) surface. A piecewise linear curve can be used to describe a trimming loop. Use trimming loop definitions within surface definitions, as defined by the **bgnsurface** subroutine.

The trimming loops are closed curves that the system uses to set the boundaries of a NURBS surface. Describe a
trimming loop by using a series of NURBS curves (as defined by the **nurbscurve** subroutine), piecewise linear curves, or both. 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.

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** subroutine. To mark the end of a trimming loop definition, use an **endtrim** subroutine.

The system displays the region of the NURBS surface that is to the left of the trimming curves as the parameter increases. Thus, for a counterclockwise-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.

This subroutine is part of GL in the AIXwindows Environment/6000 Version 1, Release 2 with AIXwindows/3D Feature.

/usr/include/gl/gl.h |
Contains C language constant and variable type definitions for GL. |

/usr/include/gl/fgl.h |
Contains FORTRAN constant and variable type definitions for GL. |

Marking the beginning and end of a NURBS surface trimming loop with the **bgntrim** and **endtrim** subroutines.

Marking the beginning and end of a NURBS surface definition with the **bgnsurface **and **endsurface** subroutines.

Returning the current value of a trimmed NURBS surfaces display property with the **getnurbsproperty** subroutine.

Controlling the shape of a NURBS trimming curve with the **nurbscurve** subroutine.

Controlling the shape of a NURBS surface with the **nurbssurface** subroutine.

Setting a property for the display of trimmed NURBS with the **setnurbsproperty** subroutine.

AIX Graphics Library Overview and Drawing NURBS Curves and Surfaces.