
GLMAP2(3G) OpenGL Manual GLMAP2(3G)
NAME
glMap2  define a twodimensional evaluator
C SPECIFICATION
void glMap2f(GLenum target, GLfloat u1, GLfloat u2, GLint ustride, GLint uorder,
GLfloat v1, GLfloat v2, GLint vstride, GLint vorder, const GLfloat * points);
void glMap2d(GLenum target, GLdouble u1, GLdouble u2, GLint ustride, GLint uorder,
GLdouble v1, GLdouble v2, GLint vstride, GLint vorder,
const GLdouble * points);
PARAMETERS
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 are evaluated by the equations specified by this command. Initially, u1
is 0 and u2 is 1.
ustride
Specifies 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 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. The initial value of ustride is 0.
uorder
Specifies the dimension of the control point array in the u axis. Must be positive.
The initial value is 1.
v1, v2
Specify a linear mapping of v, as presented to glEvalCoord2(), to v^, one of the two
variables that are evaluated by the equations specified by this command. Initially, v1
is 0 and v2 is 1.
vstride
Specifies 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 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. The initial value of vstride is 0.
vorder
Specifies the dimension of the control point array in the v axis. Must be positive.
The initial value is 1.
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 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 Bspline surfaces, NURBS
surfaces, Bezier surfaces, and so on.
Evaluators define surfaces based on bivariate Bernstein polynomials. Define p u^ v^ as
_ _
p u^ v^ = > i = 0 n > j = 0 m B i n u^ B j m v^ R ij
where R ij is a control point, B i n u^ is the ith Bernstein polynomial of degree n
(uorder = n + 1)
B i n u^ = n i u^ i 1  u^ n  i
and B j m v^ is the jth Bernstein polynomial of degree m (vorder = m + 1)
B j m v^ = m j v^ j 1  v^ m  j
Recall that 0 0 == 1 and n 0 == 1
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
u^ = u  u1 u2  u1
v^ = v  v1 v2  v1
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 floatingpoint 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 floatingpoint 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 floatingpoint 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_MAP2_COLOR_4
Each control point is four floatingpoint 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_MAP2_NORMAL
Each control point is three floatingpoint 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_MAP2_TEXTURE_COORD_1
Each control point is a single floatingpoint 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_MAP2_TEXTURE_COORD_2
Each control point is two floatingpoint 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_MAP2_TEXTURE_COORD_3
Each control point is three floatingpoint 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_MAP2_TEXTURE_COORD_4
Each control point is four floatingpoint 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.
ustride, uorder, vstride, vorder, 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.
There are uorder x vorder control points in the array. ustride specifies how many float
or double locations are skipped to advance the internal memory pointer from control point
R i j to control point R i + 1 j. vstride specifies how many float or double locations
are skipped to advance the internal memory pointer from control point R i j to control
point R i j + 1.
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 glMap2 before glMap2 returns. Changes to the contents of points
have no effect after glMap2 is called.
Initially, GL_AUTO_NORMAL is enabled. If GL_AUTO_NORMAL is enabled, normal vectors are
generated when either GL_MAP2_VERTEX_3 or GL_MAP2_VERTEX_4 is used to generate vertices.
ERRORS
GL_INVALID_ENUM is generated if target is not an accepted value.
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 1 or greater than
the return value of GL_MAX_EVAL_ORDER.
GL_INVALID_OPERATION is generated if glMap2 is executed between the execution of glBegin()
and the corresponding execution of glEnd().
GL_INVALID_OPERATION is generated if glMap2 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_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
SEE ALSO
glBegin(), glColor(), glEnable(), glEvalCoord(), glEvalMesh(), glEvalPoint(), glMap1(),
glMapGrid(), glNormal(), glTexCoord(), glVertex()
COPYRIGHT
Copyright (C) 19912006 Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 06/10/2014 GLMAP2(3G) 
