NAME
glMap1d, glMap1f - 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,
GLfloat u1,
GLfloat 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 ^, 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: B-
splines, Bezier curves, Hermite splines, and so on.
Evaluators define curves based on Bernstein polynomials.
Define p(^) as
n
R n
p(^) = i=0Bi(^)Ri
where R is a control point and Bn(^) is the ith Bernstein
polynomial of degree n (order = n+1):
n (n ) i n-i
Bi(^) = | |^ (1-^)
(i )
Recall that
0 (n )
0 = 1 and | | = 1
( 0 )
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 ^, where
^ = _______
u2 - u1
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 but the current index
is not updated with the value of
these glIndex commands.
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
but the current color is not
updated with the value of these
glColor4 commands.
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 but the current normal
is not updated with the value of
these glNormal commands.
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 but the
current texture coordinates are not
updated with the value of these
glTexCoord commands.
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 but the
current texture coordinates are not
updated with the value of these
glTexCoord commands.
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 but the current
texture coordinates are not updated
with the value of these glTexCoord
commands.
GL_MAP1_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 but the
current texture coordinates are not
updated with the value of these
glTexCoord commands.
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 specifies 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 glMap1 returns. 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 1 or
greater than the return value of GL_MAX_EVAL_ORDER.
GL_INVALID_OPERATION is generated if glMap1 is executed
between the execution of glBegin and the corresponding
execution of 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