# glEvalPoint

## Name

glEvalPoint — generate and evaluate a single point in a mesh

## C Specification

 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 $j$ (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 $j · Δ v + v 1$ 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