Light | Dark

# docs.GL

OpenGL 3
OpenGL 2

# 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`

## See Also

glEvalCoord, glEvalMesh, glMap1, glMap2, glMapGrid

## Copyright

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/.

Think you can improve this page? Edit this page on GitHub.