glMap1
NAME
glMap1 -- define a one-dimensional evaluator
C SPECIFICATION
void glMap1d(GLenum target,
GLdouble u1,
GLdouble u2,
GLint stride,
GLint order,
const GLdouble *points)
void glMap1f(GLenum target,
GLdouble u1,
GLdouble u2,
GLint stride,
GLint order,
const GLfloat *points)
PARAMETERS
- target
-
Specifies the kind of values that are generated by the evaluator.
Symbolic constants GL_MAP1_VERTEX_3, GL_MAP1_VERTEX_4,
GL_MAP1_INDEX, GL_MAP1_COLOR_4, GL_MAP1_NORMAL,
GL_MAP1_TEXTURE_COORD_1, GL_MAP1_TEXTURE_COORD_2,
GL_MAP1_TEXTURE_COORD_3, and GL_MAP1_TEXTURE_COORD_4 are
accepted.
- u1, u2
-
Specify a linear mapping of u, as presented to
glEvalCoord1, to
u^, the variable that is evaluated by the equations
specified by this command.
- stride
-
Specifies the number of floats or doubles between the beginning of one
control point and the beginning of the next one in the data structure
referenced in points. 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.
- order
-
Specifies the number of control points. Must be positive.
- 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 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 splines used in computer graphics, including B-splines,Bezier curves, Hermite splines, and so on.
Evaluators define curves based on Bernstein polynomials. Define
p(u^) as
Where Ri is a control point and Bni(u^) is the
ith Bernstein
polynomial of degree n (order = n + 1):
Recall that
glMap1 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.
glEvalCoord1 evaluates the
one-dimensional maps that are enabled. When
glEvalCoord1 presents a value
u the Bernstein functions are evaluated using u^, 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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_TEXTURE_COORD_4
-
Each control point is three 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.
stride, order, 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. order is the number
of control points in the array. stride tells how many float or double
locations to advance the internal memory pointer to reach the next control
point.
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 glMap1 before it returned.
Changes to the contents of points have no effect after glMap1 is
called.
ERRORS
GL_INVALID_ENUM is generated if target is not an accepted
value.
GL_INVALID_VALUE is generated if u1 is equal to u2.
GL_INVALID_VALUE is generated if stride is less than the
number of values in a control point.
GL_INVALID_VALUE is generated if order is less than one or
greater than GL_MAX_EVAL_ORDER.
GL_INVALID_OPERATION is generated if glMap1 is called
between a call to glBegin and the
corresponding call to glEnd.
ASSOCIATED GETS
glGetMap
glGet with argument
GL_MAX_EVAL_ORDER
glIsEnabled with argument
GL_MAP1_VERTEX_3
glIsEnabled with argument
GL_MAP1_VERTEX_4
glIsEnabled with argument
GL_MAP1_INDEX
glIsEnabled with argument
GL_MAP1_COLOR_4
glIsEnabled with argument
GL_MAP1_NORMAL
glIsEnabled with argument
GL_MAP1_TEXTURE_COORD_1
glIsEnabled with argument
GL_MAP1_TEXTURE_COORD_2
glIsEnabled with argument
GL_MAP1_TEXTURE_COORD_3
glIsEnabled with argument
GL_MAP1_TEXTURE_COORD_4
SEE ALSO
glBegin,
glColor,
glEnable,
glEvalCoord,
glEvalMesh,
glEvalPoint,
glMap2,
glMapGrid,
glNormal,
glTexCoord,
glVertex
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© 1995 Uwe Behrens. All rights reserved.