1991-2006 Silicon Graphics, Inc.

glMap1

3G

glMap1

define a one-dimensional evaluator

# C Specification

                    void glMap1f
                    GLenum target
                    GLfloat u1
                    GLfloat u2
                    GLint stride
                    GLint order
                    const GLfloat * points

                    void glMap1d
                    GLenum target
                    GLdouble u1
                    GLdouble u2
                    GLint stride
                    GLint order
                    const GLdouble * points

## Parameters

`target`

- Specifies the kind of values that are generated by the evaluator. Symbolic constants `GL_MAP1_VERTEX_3`, `GL_MAP1_VERTEX_4`, `GL_MAP1_INDEX`, `GL_MAP1_COLOR_4`, `GL_MAP1_NORMAL`, `GL_MAP1_TEXTURE_COORD_1`, `GL_MAP1_TEXTURE_COORD_2`, `GL_MAP1_TEXTURE_COORD_3`, and `GL_MAP1_TEXTURE_COORD_4` are accepted.

`u1`

`u2`

- Specify a linear mapping of u, as presented to

  glEvalCoord1

  , to u^ , the variable that is evaluated by the equations specified by this command.

`stride`

- Specifies the number of floats or doubles between the beginning of one control point and the beginning of the next one in the data structure referenced in `points`. This allows control points to be embedded in arbitrary data structures. The only constraint is that the values for a particular control point must occupy contiguous memory locations.

`order`

- Specifies the number of control points. Must be positive.

`points`

- Specifies a pointer to the array of control points.

## Description

Evaluators provide a way to use polynomial or rational polynomial mapping to produce vertices, normals, texture coordinates, and colors. The values produced by an evaluator are sent to further stages of GL processing just as if they had been presented using

glVertex

,

glNormal

,

glTexCoord

, and

glColor

commands, except that the generated values do not update the current normal, texture coordinates, or color.

All polynomial or rational polynomial splines of any degree (up to the maximum degree supported by the GL implementation) can be described using evaluators. These include almost all splines used in computer graphics: B-splines, Bezier curves, Hermite splines, and so on.

Evaluators define curves based on Bernstein polynomials. Define p ⁡ u^ as

p ⁡ u^ = Σ i = 0 n B i n ⁡ u^ ⁢ R i

where R i is a control point and B i n ⁡ u^ is the ith Bernstein polynomial of degree n (`order` = n + 1 ):

B i n ⁡ u^ = n i ⁢ u^ i ⁢ 1 - u^ n - i

Recall that

0 0 == 1 and n 0 == 1

`glMap1` is used to define the basis and to specify what kind of values are produced. Once defined, a map can be enabled and disabled by calling

glEnable

and

glDisable

with the map name, one of the nine predefined values for `target` described below.

glEvalCoord1

evaluates the one-dimensional maps that are enabled. When

glEvalCoord1

presents a value u, the Bernstein functions are evaluated using u^ , where u^ = u - u1 u2 - u1

`target` is a symbolic constant that indicates what kind of control points are provided in `points`, and what output is generated when the map is evaluated. It can assume one of nine predefined values:

`GL_MAP1_VERTEX_3`

- Each control point is three floating-point values representing x, y, and z. Internal

  glVertex3

  commands are generated when the map is evaluated.

`GL_MAP1_VERTEX_4`

- Each control point is four floating-point values representing x, y, z, and w. Internal

  glVertex4

  commands are generated when the map is evaluated.

`GL_MAP1_INDEX`

- Each control point is a single floating-point value representing a color index. Internal

  glIndex

  commands are generated when the map is evaluated but the current index is not updated with the value of these

  glIndex

  commands.

`GL_MAP1_COLOR_4`

- Each control point is four floating-point values representing red, green, blue, and alpha. Internal

  glColor4

  commands are generated when the map is evaluated but the current color is not updated with the value of these

  glColor4

  commands.

`GL_MAP1_NORMAL`

- Each control point is three floating-point values representing the x, y, and z components of a normal vector. Internal

  glNormal

  commands are generated when the map is evaluated but the current normal is not updated with the value of these

  glNormal

  commands.

`GL_MAP1_TEXTURE_COORD_1`

- Each control point is a single floating-point value representing the s texture coordinate. Internal

  glTexCoord1

  commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these

  glTexCoord

  commands.

`GL_MAP1_TEXTURE_COORD_2`

- Each control point is two floating-point values representing the s and t texture coordinates. Internal

  glTexCoord2

  commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these

  glTexCoord

  commands.

`GL_MAP1_TEXTURE_COORD_3`

- Each control point is three floating-point values representing the s, t, and r texture coordinates. Internal

  glTexCoord3

  commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these

  glTexCoord

  commands.

`GL_MAP1_TEXTURE_COORD_4`

- Each control point is four floating-point values representing the s, t, r, and q texture coordinates. Internal

  glTexCoord4

  commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these

  glTexCoord

  commands.

`stride`, `order`, and `points` define the array addressing for accessing the control points. `points` is the location of the first control point, which occupies one, two, three, or four contiguous memory locations, depending on which map is being defined. `order` is the number of control points in the array. `stride` specifies how many float or double locations to advance the internal memory pointer to reach the next control point.

## Notes

As is the case with all GL commands that accept pointers to data, it is as if the contents of `points` were copied by `glMap1` before `glMap1` returns. Changes to the contents of `points` have no effect after `glMap1` is called.

## Errors

`GL_INVALID_ENUM` is generated if `target` is not an accepted value.

`GL_INVALID_VALUE` is generated if `u1` is equal to `u2`.

`GL_INVALID_VALUE` is generated if `stride` is less than the number of values in a control point.

`GL_INVALID_VALUE` is generated if `order` is less than 1 or greater than the return value of `GL_MAX_EVAL_ORDER`.

`GL_INVALID_OPERATION` is generated if `glMap1` is executed between the execution of

glBegin

and the corresponding execution of

glEnd

.

`GL_INVALID_OPERATION` is generated if `glMap1` is called and the value of `GL_ACTIVE_TEXTURE` is not `GL_TEXTURE0`.

## Associated Gets

glGetMap

glGet

with argument `GL_MAX_EVAL_ORDER`

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`

## See Also

glBegin

,

glColor

,

glEnable

,

glEvalCoord

,

glEvalMesh

,

glEvalPoint

,

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/.