glMap2d, glMap2f

[New - Windows 95, OEM Service Release 2]

The glMap2d and glMap2f functions define a two-dimensional evaluator.

void glMap2d(

void glMap2f(

Parameters

target

The kind of values that are generated by the evaluator. The following symbolic constants are accepted:

GL_MAP2_VERTEX_3

Each control point is three floating-point values representing x, y, and z. Internal glVertex30DHHRC 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 glVertex40DHHRC 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 glIndex45Y9.CK 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 glColor4OOTFYK 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 glNormal2NHAN7 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 glTexCoord1FFHXD1 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_2

Each control point is two floating-point values representing the s and t texture coordinates. Internal glTexCoord2FFHXD1 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 three floating-point values representing the s, t, and r texture coordinates. Internal glTexCoord3FFHXD1 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 four floating-point values representing the s, t, r, and q texture coordinates. Internal glTexCoord4FFHXD1 commands are generated when the map is evaluated. The current texture coordinates are not updated with the value of these glTexCoord commands, however.

u1, u2

A linear mapping of u, as presented to glEvalCoord2, to  , one of the two variables that is evaluated by the equations specified by this command.

ustride

The number of floats or doubles between the beginning of control point R (ij)  and the beginning of control point R ((i+1)j) , where i and j are the u and v control point indexes, 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

The dimension of the control point array in the u-axis. Must be positive.

v1, v2

A linear mapping of v, as presented to glEvalCoord2JY1DQM, to {bmc bm35.WMF}, one of the two variables that is evaluated by the equations specified by this command.

vstride

The number of floats or doubles between the beginning of control point R (ij)  and the beginning of control point R (i(j+1)) , where i and j are the u and v control point indexes, 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

The dimension of the control point array in the v-axis. Must be positive.

points

A pointer to the array of control points.

Remarks

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 on to further stages of OpenGL processing just as if they had been presented using glVertex0DHHRC, glNormal2NHAN7, glTexCoordFFHXD1, and glColorOOTFYK 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 OpenGL 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( ,{bmc bm36.WMF}) as

{bml bm37.BMP}

where R (ij)  is a control point, {bmc bm38.WMF} ( ) is the ith Bernstein polynomial of degree

n (uorder = n + 1)

{bml bm39.BMP}

and ({bmc bm40.WMF}) is the jth Bernstein polynomial of degree m (vorder = m + 1)

{bml bm41.BMP}

Recall that

{bml bm42.BMP}

The glMap2 function 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 glEnable194O61P and glDisable with the map name, one of the nine predefined values for target, described above. When glEvalCoord2JY1DQM presents values u and v, the bivariate Bernstein polynomials are evaluated using   and {bmc bm43.WMF}, where

{bml bm44.BMP}

{bml bm45.BMP}

The target parameter 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.

The ustride, uorder, vstride, vorder, and points parameters define the array addressing for accessing the control points. The points parameter 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. There are uorderxvorder control points in the array. The ustride parameter tells how many float or double locations are skipped to advance the internal memory pointer from control point R (ij)  to control point R ((i+1)j) . The vstride parameter tells how many float or double locations are skipped to advance the internal memory pointer from control point R (ij)  to control point R (i(j+1)) .

As is the case with all OpenGL commands that accept pointers to data, it is as if the contents of points were copied by glMap2 before it returned. Changes to the contents of points have no effect after glMap2 is called.

The following functions retrieve information related to glMap2:

glGet8KNKTW with argument GL_MAX_EVAL_ORDER

glGetMapHMVA0K

glIsEnabled1MZ_ZK. 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

Error Codes

The following are the error codes generated and their conditions.

See Also