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*GL3.2 for AIX: Graphics Library (GL) Technical Reference*

## crvn Subroutine

### Purpose

Draws a series of curve segments.

### Libraries

Graphics Library

C (**libgl.a**)

FORTRAN (**libfgl.a**)

### C Syntax

**void crvn(Int32 ***n***, Coord ***geom*** [ ][3])**

### FORTRAN Syntax

**SUBROUTINE CRVN(***n***, ***geom***)**
**INTEGER*4*** n*
**REAL ***geom***(3, ***n***)**

### Description

The **crvn **subroutine draws a series of
cubic spline
segments using the current basis and precision. The control points determine the shapes of the curve segments and are used sequentially four at a time.

For example, if there are six control points, there are three possible sequential selections of four control points. Thus, **crvn** draws three curve segments: the first using control points 0,1,2,3; the second using control points 1,2,3,4; and the third using control points 2,3,4,5.

If the current basis is a
B-spline, a
Cardinal spline, or a basis with similar properties, the curve segments are joined end to end and appear as a single curve.

### Parameters

*geom* |
Specifies a matrix of 3-D points. |

*n* |
Number of points in the matrix referenced by *geom*. |

### Example

The example C language program **curve2.c** uses the **crvn** subroutine to draw a curve with six control points.

### Implementation Specifics

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

### Files

**/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. |

### Related Information

Drawing a cubic spline curve with the **crv** subroutine.

Setting the current cubic spline curve basis matrix with the **curvebasis** subroutine.

Setting the number of line segments that compose a cubic spline curve with the **curveprecision** subroutine.

Defining a cubic spline basis matrix with the **defbasis** subroutine.

Drawing a rational curve with the **rcrv** subroutine.

Drawing a series of rational curve segments with the **rcrvn** subroutine.

AIX Graphics Library Overview, Drawing NURBS Curves and Surfaces, and Drawing Wire Frame Curves and Surface Patches.

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