glEvalPoint
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## Name

glEvalPoint1, glEvalPoint2 — generate and evaluate a single point in a mesh

## C Specification

`void `glEvalPoint1`` | `(` | `GLint `i`);`
`void `glEvalPoint2`` | `(` | `GLint `i`, GLint `j`);`

## Python Specification

``glEvalPoint1`` | `(` | ``i`) → `None``
``glEvalPoint2`` | `(` | ``i`, `j`) → `None``

## 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 · Δ u + u 1 );

where Δ u = ( u 2 - u 1 ) / n

and n , u 1 , and u 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 · Δ u + u 1 is exactly u 2 .

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

Δ u = ( u 2 - u 1 ) / n Δ 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` command. Then the `glEvalPoint2` command is equivalent to calling

glEvalCoord2( i · Δ u + u 1 , j · Δ v + v 1 );

The only absolute numeric requirements are that if i = n , then the value computed from i · Δ u + u 1 is exactly u 2 , and if j = m , then the value computed from i · Δ v + v 1 is exactly v 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, glEvalMesh, glMap1, glMap2, glMapGrid

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