---
name: "glEvalPoint"
section: "3x"
platform: "linux"
package: "xlibmesa-gl-dev"
version: "4.3.0.dfsg.1-14sarge7"
release: "Debian 3.1 (Sarge)"
platforms: ["linux"]
url: "https://new.carta.tech/glEvalPoint"
---

# glEvalPoint(3x)

generate and evaluate a single point in a mesh

## NAME

**glEvalPoint1, glEvalPoint2** - generate and evaluate a single point in a mesh

## C SPECIFICATION

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

```

```

void **glEvalPoint2**( GLint *i*,

```
	GLint j )
```

delim $$

## PARAMETERS

- *i*

  Specifies the integer value for grid domain variable $i$.

- *j*

  Specifies the integer value for grid domain variable $j$ (**glEvalPoint2** only).

## DESCRIPTION

**glMapGrid** and **glEvalMesh** 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 gridspace that is traversed by **glEvalMesh**. Calling **glEvalPoint1** is equivalent to calling

```

```

-

  glEvalCoord1( i$^cdot^DELTA u ~+~ u sub 1$ );

  where

  $DELTA u ~=~ ( u sub 2 - u sub 1 ) ^/^ n$

and $n$, $u sub 1$, and $u sub 2$ are the arguments to the most recent **glMapGrid1** command. The one absolute numeric requirement is that if $i~=~n$, then the value computed from  $i ^cdot^ DELTA u ~+~ u sub 1$ is exactly $u sub 2$.

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

```

```

-

  $DELTA u ~=~ mark ( u sub 2 - u sub 1 ) ^/^ n$

  $DELTA v ~=~ mark ( v sub 2 - v sub 1 ) ^/^ m,$

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

```

```

-

  glEvalCoord2( i$^cdot^DELTA u ~+~ u sub 1$, j$^cdot^DELTA v ~+~ v sub 1$ );

  The only absolute numeric requirements are that if $i~=~n$, then the value computed from $i ^cdot^DELTA u ~+~ u sub 1$ is exactly $u sub 2$, and if $j~=~m$, then the value computed from  $i ^cdot^DELTA v ~+~ v sub 1$ is exactly $v sub 2$.

## ASSOCIATED GETS

**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**

## SEE ALSO

**glEvalCoord(3G)**, **glEvalMesh(3G)**, **glMap1(3G)**, **glMap2(3G)**, **glMapGrid(3G)**