glMap2d, glMap2f - define a two-dimensional evaluator

void glMap2d( GLenumtarget, GLdoubleu1, GLdoubleu2, GLintustride, GLintuorder, GLdoublev1, GLdoublev2, GLintvstride, GLintvorder, const GLdouble *points) void glMap2f( GLenumtarget, GLfloatu1, GLfloatu2, GLintustride, GLintuorder, GLfloatv1, GLfloatv2, GLintvstride, GLintvorder, const GLfloat *points)

targetSpecifies 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,u2Specify a linear mapping of u, as presented to glEvalCoord2, tou, one of the two variables that is evaluated by the equations specified by this command.ustrideSpecifies the number of floats or doubles between the beginning of control point R and the beginning of control point R , ij (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.uorderSpecifies the dimension of the control point array in the u axis. Must be positive.v1,v2Specify a linear mapping of v, as presented to glEvalCoord2, tov, one of the two variables that is evaluated by the equations specified by this command.vstrideSpecifies the number of floats or doubles between the beginning of control point R and the beginning of control point R , ij (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.vorderSpecifies the dimension of the control point array in the v axis. Must be positive.pointsSpecifies a pointer to the array of control points.

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 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 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 n m --- --- \ \ n m p(u,v) = \ \ B (u)B (v) R / / i j ij / / --- --- i=0 j=0 n where R is a control point, B (u) is the ith Bernstein polynomial of ij i degree n (uorder= n+1) n |n| i n-i B (u) = | |u(1-u) i |i| m and B (v') is the jth Bernstein polynomial of degree m (vorder= m+1) j m |m| j m-j B (v) = | |v(1-v) j |j| Recall that 0 |n| 0 = 1 and | | = 1 |0| 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 fortarget, described below. When glEvalCoord2 presents values u and v, the bivariate Bernstein polynomials are evaluated usinguandv, where u - u1u= ------- u2 - u1 v - v1v= ------- v2 - v1targetis a symbolic constant that indicates what kind of control points are provided inpoints, 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 glTexCoord commands, however. GL_MAP2_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. 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 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 four floating-point values 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.ustride,uorder,vstride,vorder, andpointsdefine the array addressing for accessing the control points.pointsis 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.ustridetells how many float or double locations are skipped to advance the internal memory pointer from control point R to control point R .vstridetells how many float ij (i+1)j or double locations are skipped to advance the internal memory pointer from control point R to control point R . ij i(j+1)

As is the case with all GL commands that accept pointers to data, it is as if the contents ofpointswere copied by glMap2 before it returned. Changes to the contents ofpointshave no effect after glMap2 is called.

GL_INVALID_ENUM is generated iftargetis not an accepted value. GL_INVALID_VALUE is generated ifu1is equal tou2, or ifv1is equal tov2. GL_INVALID_VALUE is generated if eitherustrideorvstrideis less than the number of values in a control point. GL_INVALID_VALUE is generated if eitheruorderorvorderis less than one or greater than GL_MAX_EVAL_ORDER. GL_INVALID_OPERATION is generated if glMap2 is executed between the execution of glBegin and the corresponding execution of glEnd.

glGetMap glGet with argument GL_MAX_EVAL_ORDER 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

glBegin, glColor, glEnable, glEvalCoord, glEvalMesh, glEvalPoint, glMap1, glMapGrid, glNormal, glTexCoord, glVertex

Introduction | Alphabetic | Specification

Last Edited: *
Fri Dec 6 11:18:03 EST 1996
*
by
*AFV*

Look here for legal stuff: Legal