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

## rpatch Subroutine

### Purpose

Draws a rational surface patch.

### Libraries

Graphics Library

C (**libgl.a**)

FORTRAN (**libfgl.a**)

### C Syntax

**void rpatch**
**(Matrix ***geomx***, Matrix** *geomy***,**
**Matrix** *geomz***, Matrix** *geomw***)**

### FORTRAN Syntax

**SUBROUTINE RPATCH(***geomx*, *geomy*, *geomz, geomw***)**
**REAL ***geomx***(4,4), ***geomy***(4,4), ***geomz***(4,4), ***geomw***(4,4)**

### Description

The **rpatch** subroutine draws a rational
surface patch using the current settings from the **patchbasis**, **patchprecision**, and **patchcurves** subroutines. The
control points *geomx*, *geomy*, *geomz**, *and *geomw* determine the shape of the patch.

### Parameters

*geomx* |
Specifies a 4x4 matrix containing the *x* coordinates of the 16 control points of the patch. |

*geomy* |
Specifies a 4x4 matrix containing the *y* coordinates of the 16 control points of the patch. |

*geomz* |
Specifies a 4x4 matrix containing the *z* coordinates of the 16 control points of the patch. |

*geomw* |
Specifies a 4x4 matrix containing the *w* coordinates of the 16 control points of the patch. |

### 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

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

Drawing a surface patch with the **patch** subroutine.

Setting the current spline surface basis matrices with the **patchbasis** subroutine.

Setting the number of curves used to represent a patch with the **patchcurves** subroutine.

Setting the precision at which curves are drawn with the **patchprecision** subroutine.

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

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