glEvalPoint.3G - Man Page

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$\text{}·\text{}\Delta u\text{ }+\text{ }{u}_{1}$ );`

where

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

and $n$, ${u}_{1}$, and ${u}_{2}$ are the arguments to the most recent glMapGrid1 command. The one absolute numeric requirement is that if $i\text{ }=\text{ }n$, then the value computed from  $i\text{}·\text{}\Delta u\text{ }+\text{ }{u}_{1}$ is exactly ${u}_{2}$.

In the two-dimensional case, glEvalPoint2, let

```$\Delta u\text{ }=\text{ }\left({u}_{2}-{u}_{1}\right)\text{}/\text{}n$

$\Delta v\text{ }=\text{ }\left({v}_{2}-{v}_{1}\right)\text{}/\text{}m,$```

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$\text{}·\text{}\Delta u\text{ }+\text{ }{u}_{1}$, j$\text{}·\text{}\Delta v\text{ }+\text{ }{v}_{1}$ );`

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