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/comp/gb.opengl/gl/evalpoint1

# Gl.EvalPoint1 (gb.opengl)

Static Sub EvalPoint1 ( I As Integer )

Generate and evaluate a single point in a mesh.

### Parameters

i

  Specifies the integer value for grid domain variable i.

j

  Specifies the integer value for grid domain variable 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
    ·
    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 Gl.MapGrid1 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, Gl.EvalPoint2, 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 Gl.MapGrid2 command. Then the Gl.EvalPoint2 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 j · Δ v + v 1 is exactly 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