voidglMap2d(GLenumtarget, GLdoubleu1, GLdoubleu2, GLintustride, GLintuorder, GLdoublev1, GLdoublev2, GLintvstride, GLintvorder, const GLdouble *points) voidglMap2f(GLenumtarget, GLdoubleu1, GLdoubleu2, GLintustride, GLintuorder, GLdoublev1, GLdoublev2, GLintvstride, GLintvorder, const GLfloat *points)

*target*-
Specifies the kind of values that are generated by the evaluator.
Symbolic constants
**GL_MAP2_VERTEX_3**,**GL_MAP2_VERTEX_4**,**GL_MAP2_INDEX**,**GL_MAP2_COLOR_4**,**GL_MAP2_NORMAL**,**GL_MAP2_TEXTURE_COORD_1**,**GL_MAP2_TEXTURE_COORD_2**,**GL_MAP2_TEXTURE_COORD_3**, and**GL_MAP2_TEXTURE_COORD_4**are accepted. *u1*,*u2*-
Specify a linear mapping of
*u*, as presented to**glEvalCoord2**, to*u^*, one of the two variables that is evaluated by the equations specified by this command. *ustride*-
Specifies the number of floats or doubles between the beginning
of control point
*Rij*and the beginning of control point*R*(*i*+1)*j*, where*i*and*j*are the*u*and*v*control point indices, respectively. 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. *uorder*-
Specifies the dimension of the control point array in the
*u*axis. Must be positive. *v1*,*v2*-
Specify a linear mapping of
*v*, as presented to**glEvalCoord2**, to*v^*, one of the two variables that is evaluated by the equations specified by this command. *vstride*-
Specifies the number of floats or doubles between the beginning
of control point
*Rij*and the beginning of control point*Ri*(*j*+1), where*i*and*j*are the*u*and*v*control point indices, respectively. 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. *vorder*-
Specifies the dimension of the control point array in the
*v*axis. Must be positive. *points*- Specifies a pointer to the array of control points.

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 surfaces used in computer graphics, including B-spline surfaces, NURBS surfaces, Bezier surfaces, and so on.

Evaluators define surfaces based on bivariate Bernstein polynomials. Define
*p*(*u^*,*v^*) as

where *Rij* is a control point, *Bni*(*u^*) is the
*i*th Bernstein polynomial of degree *n*
(*uorder* = *n* + 1)

and *Bmj*(*v^*) is the *j*th Bernstein polynomial of degree
*m* (*vorder* = *m* + 1)

Recall that

**glMap2** 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. When
**glEvalCoord2** presents values
*u* and *v*, the bivariate Bernstein polynomials are evaluated
using *u^* and *v^*, where

*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_MAP2_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_MAP2_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_MAP2_INDEX**-
Each control point is a single floating-point value representing a
color index. Internal
**glIndex**commands are generated when the map is evaluated. The current index is not updated with the value of these**glIndex**commands, however. **GL_MAP2_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. The current color is not updated with the value of these**glColor4**commands however. **GL_MAP2_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. The current normal is not updated with the value of these**glNormal**commands, however. **GL_MAP2_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. The current texture coordinates are not updated with the value of these**glTexCoord1**commands, however. **GL_MAP2_TEXTURE_COORD_2**-
Each control point is a single floating-point value representing the
*s*and*t*texture coordinates. Internal**glTexCoord2**commands are generated when the map is evaluated. The current texture coordinates are not updated with the value of these**glTexCoord**commands, however. **GL_MAP2_TEXTURE_COORD_3**-
Each control point is a single floating-point value representing the
*s*,*t*and*r*texture coordinates. Internal**glTexCoord3**commands are generated when the map is evaluated. The current texture coordinates are not updated with the value of these**glTexCoord**commands, however. **GL_MAP2_TEXTURE_COORD_4**-
Each control point is a single floating-point value representing the
*s*,*t*,*r*and*q*texture coordinates. Internal**glTexCoord4**commands are generated when the map is evaluated. The current texture coordinates are not updated with the value of these**glTexCoord**commands, however.

**GL_INVALID_VALUE** is generated if *u1* is equal to *u2*, or
if *v1*is equal to *v2*.

**GL_INVALID_VALUE** is generated if either *ustride* or *vstride*
is less than the number of values in a control point.

**GL_INVALID_VALUE** is generated if either *uorder* or *vorder*
is less than one or greater than **GL_MAX_VAL_ORDER**.

**GL_INVALID_OPERATION** is generated if **glMap2** is called between
a call to **glBegin** and the corresponding
call to **glEnd**.

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© *1995 Uwe Behrens. All rights reserved.*