1991-2006 Silicon Graphics, Inc.

glEvalCoord

3G

glEvalCoord

evaluate enabled one- and two-dimensional maps

# C Specification

                    void glEvalCoord1f
                    GLfloat u

                    void glEvalCoord1d
                    GLdouble u

                    void glEvalCoord2f
                    GLfloat u
                    GLfloat v

                    void glEvalCoord2d
                    GLdouble u
                    GLdouble v

## Parameters

`u`

- Specifies a value that is the domain coordinate u to the basis function defined in a previous

  glMap1

  or

  glMap2

  command.

`v`

- Specifies a value that is the domain coordinate v to the basis function defined in a previous

  glMap2

  command. This argument is not present in a `glEvalCoord1` command.

## C Specification

                    void glEvalCoord1fv
                    const GLfloat * u

                    void glEvalCoord1dv
                    const GLdouble * u

                    void glEvalCoord2fv
                    const GLfloat * u

                    void glEvalCoord2dv
                    const GLdouble * u

## Parameters

`u`

- Specifies a pointer to an array containing either one or two domain coordinates. The first coordinate is u. The second coordinate is v, which is present only in `glEvalCoord2` versions.

## Description

`glEvalCoord1` evaluates enabled one-dimensional maps at argument `u`. `glEvalCoord2` does the same for two-dimensional maps using two domain values, `u` and `v`. To define a map, call

glMap1

and

glMap2

; to enable and disable it, call

glEnable

and

glDisable

.

When one of the `glEvalCoord` commands is issued, all currently enabled maps of the indicated dimension are evaluated. Then, for each enabled map, it is as if the corresponding GL command had been issued with the computed value. That is, if `GL_MAP1_INDEX` or `GL_MAP2_INDEX` is enabled, a

glIndex

command is simulated. If `GL_MAP1_COLOR_4` or `GL_MAP2_COLOR_4` is enabled, a

glColor

command is simulated. If `GL_MAP1_NORMAL` or `GL_MAP2_NORMAL` is enabled, a normal vector is produced, and if any of `GL_MAP1_TEXTURE_COORD_1`, `GL_MAP1_TEXTURE_COORD_2`, `GL_MAP1_TEXTURE_COORD_3`, `GL_MAP1_TEXTURE_COORD_4`, `GL_MAP2_TEXTURE_COORD_1`, `GL_MAP2_TEXTURE_COORD_2`, `GL_MAP2_TEXTURE_COORD_3`, or `GL_MAP2_TEXTURE_COORD_4` is enabled, then an appropriate

glTexCoord

command is simulated.

For color, color index, normal, and texture coordinates the GL uses evaluated values instead of current values for those evaluations that are enabled, and current values otherwise, However, the evaluated values do not update the current values. Thus, if

glVertex

commands are interspersed with `glEvalCoord` commands, the color, normal, and texture coordinates associated with the

glVertex

commands are not affected by the values generated by the `glEvalCoord` commands, but only by the most recent

glColor

,

glIndex

,

glNormal

, and

glTexCoord

commands.

No commands are issued for maps that are not enabled. If more than one texture evaluation is enabled for a particular dimension (for example, `GL_MAP2_TEXTURE_COORD_1` and `GL_MAP2_TEXTURE_COORD_2`), then only the evaluation of the map that produces the larger number of coordinates (in this case, `GL_MAP2_TEXTURE_COORD_2`) is carried out. `GL_MAP1_VERTEX_4` overrides `GL_MAP1_VERTEX_3`, and `GL_MAP2_VERTEX_4` overrides `GL_MAP2_VERTEX_3`, in the same manner. If neither a three- nor a four-component vertex map is enabled for the specified dimension, the `glEvalCoord` command is ignored.

If you have enabled automatic normal generation, by calling

glEnable

with argument `GL_AUTO_NORMAL`, `glEvalCoord2` generates surface normals analytically, regardless of the contents or enabling of the `GL_MAP2_NORMAL` map. Let

m = ∂ p ∂ u × ∂ p ∂ v

Then the generated normal n is n = m m

If automatic normal generation is disabled, the corresponding normal map `GL_MAP2_NORMAL`, if enabled, is used to produce a normal. If neither automatic normal generation nor a normal map is enabled, no normal is generated for `glEvalCoord2` commands.

## Associated Gets

glIsEnabled

with argument `GL_MAP1_VERTEX_3`

glIsEnabled

with argument `GL_MAP1_VERTEX_4`

glIsEnabled

with argument `GL_MAP1_INDEX`

glIsEnabled

with argument `GL_MAP1_COLOR_4`

glIsEnabled

with argument `GL_MAP1_NORMAL`

glIsEnabled

with argument `GL_MAP1_TEXTURE_COORD_1`

glIsEnabled

with argument `GL_MAP1_TEXTURE_COORD_2`

glIsEnabled

with argument `GL_MAP1_TEXTURE_COORD_3`

glIsEnabled

with argument `GL_MAP1_TEXTURE_COORD_4`

glIsEnabled

with argument `GL_MAP2_VERTEX_3`

glIsEnabled

with argument `GL_MAP2_VERTEX_4`

glIsEnabled

with argument `GL_MAP2_INDEX`

glIsEnabled

with argument `GL_MAP2_COLOR_4`

glIsEnabled

with argument `GL_MAP2_NORMAL`

glIsEnabled

with argument `GL_MAP2_TEXTURE_COORD_1`

glIsEnabled

with argument `GL_MAP2_TEXTURE_COORD_2`

glIsEnabled

with argument `GL_MAP2_TEXTURE_COORD_3`

glIsEnabled

with argument `GL_MAP2_TEXTURE_COORD_4`

glIsEnabled

with argument `GL_AUTO_NORMAL`

glGetMap

## See Also

glBegin

,

glColor

,

glEnable

,

glEvalMesh

,

glEvalPoint

,

glIndex

,

glMap1

,

glMap2

,

glMapGrid

,

glNormal

,

glTexCoord

,

glVertex

## Copyright

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