glMap2 — define a two-dimensional evaluator
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) ; |
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
u1
is 0 and u2
is 1.
ustride
Specifies the number of floats or doubles between
the beginning of control point
ustride
is 0.
uorder
Specifies the dimension of the control point array in the
v1
, v2
Specify a linear mapping of
v1
is 0 and v2
is 1.
vstride
Specifies the number of floats or doubles between
the beginning of control point
vstride
is 0.
vorder
Specifies the dimension of the control point array in the
points
Specifies 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
where
uorder
=
and
vorder
=
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
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
GL_MAP2_VERTEX_4
Each control point is four floating-point values representing
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 but the current index is not updated with the value of these glIndex commands.
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 but the current color is not updated with the value of these glColor4 commands.
GL_MAP2_NORMAL
Each control point is three floating-point values representing
the
GL_MAP2_TEXTURE_COORD_1
Each control point is a single floating-point value representing
the
GL_MAP2_TEXTURE_COORD_2
Each control point is two floating-point values representing
the
GL_MAP2_TEXTURE_COORD_3
Each control point is three floating-point values representing
the
GL_MAP2_TEXTURE_COORD_4
Each control point is four floating-point values representing
the
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
ustride
specifies how many float or double locations are skipped to advance
the internal memory pointer from control point
vstride
specifies how many float or double locations are skipped to advance
the internal memory pointer from control point
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.
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
.
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
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/.