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Gl.EvalPoint2 (gb.opengl)
`Static Sub EvalPoint2 ( I As Integer, J As Integer )`

Generate and evaluate a single point in a mesh.

### Parameters

i

Specifies the integer value for grid domain variable $\mathit{i}$.

j

Specifies the integer value for grid domain variable $\mathit{j}$ (Gl.EvalPoint2 only).

### Description

Gl.MapGrid and Gl.EvalMesh are used in tandem to efficiently generate and evaluate a series of evenly spaced map domain values. Gl.EvalPoint can be used to evaluate a single grid point in the same gridspace that is traversed by Gl.EvalMesh. Calling Gl.EvalPoint1 is equivalent to calling

```glEvalCoord1( $i·\Delta \mathit{u}+{\mathit{u}}_{1}$ );
```

where $\Delta \mathit{u}=\frac{\left({\mathit{u}}_{2}-{\mathit{u}}_{1}\right)}{\mathit{n}}$

and $\mathit{n}$, ${\mathit{u}}_{1}$, and ${\mathit{u}}_{2}$ are the arguments to the most recent Gl.MapGrid1 command. The one absolute numeric requirement is that if $\mathit{i}=\mathit{n}$, then the value computed from $\mathit{i}·\Delta \mathit{u}+{\mathit{u}}_{1}$ is exactly ${\mathit{u}}_{2}$.

In the two-dimensional case, Gl.EvalPoint2, let

$\Delta \mathit{u}=\frac{\left({\mathit{u}}_{2}-{\mathit{u}}_{1}\right)}{\mathit{n}}$

$\Delta \mathit{v}=\frac{\left({\mathit{v}}_{2}-{\mathit{v}}_{1}\right)}{\mathit{m}}$

where $\mathit{n}$, ${\mathit{u}}_{1}$, ${\mathit{u}}_{2}$, $\mathit{m}$, ${\mathit{v}}_{1}$, and ${\mathit{v}}_{2}$ are the arguments to the most recent Gl.MapGrid2 command. Then the Gl.EvalPoint2 command is equivalent to calling

```glEvalCoord2( $i·\Delta \mathit{u}+{\mathit{u}}_{1},j·\Delta \mathit{v}+{\mathit{v}}_{1}$ );
```

The only absolute numeric requirements are that if $\mathit{i}=\mathit{n}$, then the value computed from $\mathit{i}·\Delta \mathit{u}+{\mathit{u}}_{1}$ is exactly ${\mathit{u}}_{2}$, and if $\mathit{j}=\mathit{m}$, then the value computed from $\mathit{j}·\Delta \mathit{v}+{\mathit{v}}_{1}$ is exactly ${\mathit{v}}_{2}$.

### Associated Gets

Gl.Get with argument Gl.MAP1_GRID_DOMAIN

Gl.Get with argument Gl.MAP2_GRID_DOMAIN

Gl.Get with argument Gl.MAP1_GRID_SEGMENTS

Gl.Get with argument Gl.MAP2_GRID_SEGMENTS

### See also

Gl.EvalCoord, Gl.EvalMesh, Gl.Map1, Gl.Map2, Gl.MapGrid

See original documentation on OpenGL website
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