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*OpenGL 1.1 for AIX: Reference Manual*

## glEvalPoint Subroutine

### Purpose

Generates and evaluates a single point in a mesh.

### Library

OpenGL C bindings library: **libGL.a**

### C Syntax

**void glEvalPoint1(GLint ***i***)**

**void glEvalPoint2(GLint ***i***,**
** GLint ***j***)**

### Parameters

*i* |
Specifies the integer value for grid domain variable *i*. |

*j* |
Specifies the integer value for grid domain variable *j*. (This parameter applies to **glEvalPoint2** only.) |

### Description

The **glMapGrid** and **glEvalMesh** subroutines are used in tandem to efficiently generate and evaluate a series of evenly spaced map domain values. **glEvalPoint** can be used to evaluate a single grid point in the same grid space that is traversed by **glEvalMesh**. Calling **glEvalPoint1** is equivalent to calling

EvalCoord1(*i* (DELTA *u*) + *u*1);

where DELTA *u* = (*u*2 - *u*1)/*n* and *n*, *u*1, and *u*2 are the arguments to the most recent **glMapGrid1** subroutine. The one absolute numeric requirement is that if *i* = *n*, the value computed from *i* (DELTA *u*) + *u*1 is exactly *u*2.

In the two-dimensional case, **glEvalPoint2**, let

DELTA *u* = (*u*2 - *u*1 )/*n*
DELTA *v* = (*v*2 - *v*1 )/*m*

where *n*, *u*1, *u*2, *m*, *v*1, and *v*2 are the arguments to the most recent **glMapGrid2** subroutine. Then the **glEvalPoint2** subroutine is equivalent to calling:

EvalCoord2(*i* (DELTA *u*) + *u*1,
*j* (DELTA *v*) + *v*1)

The only absolute numeric requirements are that if *i* = *n*, the value computed from *i *(DELTA *u*) + *u*1 is exactly *u*2, and if *j* = *m*, the value computed from *j *(DELTA *v*) + *v*1 is exactly *v*2.

### Associated Gets

Associated gets for the **glEvalPoint **subroutine are as follows. (See the **glGet** subroutine for more information.)

**glGet** with argument **GL_MAP1_GRID_DOMAIN**

**glGet** with argument **GL_MAP2_GRID_DOMAIN**

**glGet** with argument **GL_MAP1_GRID_SEGMENTS**

**glGet** with argument **GL_MAP2_GRID_SEGMENTS**.

### Files

**/usr/include/GL/gl.h** |
Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL. |

### Related Information

The **glEvalCoord** subroutine, **glEvalMesh** subroutine, **glMap1** subroutine, **glMap2** subroutine, **glMapGrid** subroutine.

OpenGL Overview.

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