glMap1, glMap1d, glMap1f - define a one-dimensional evaluator
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 );
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. Specify a linear mapping of u,
as presented to glEvalCoord1(), to u hat, the variable
that is evaluated by the equations specified by this command.
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. Specifies the number of control points.
Must be positive. 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 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: Bsplines,
Bezier curves, Hermite splines, and so on.
Evaluators define curves based on Bernstein polynomials.
Define p ( u hat ) as p ( u hat ) { sum from i=0 to n }
B[i] sup n ( u hat ) R[i]
where R[i] is a control point and B[i] sup n ( u hat ) is
the ith Bernstein polynomial of degree n (order = n + 1):
B[i] sup n ( u hat ) { n above i }} u hat sup i ( 1 - u
hat ) sup { n - i }
Recall that 0 sup 0 == 1 { n above 0 }} right ) == 1
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 onedimensional
maps that are enabled. When glEvalCoord1()
presents a value u, the Bernstein functions are evaluated
using u hat, where u hat = {u - "u1"} over {"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: Each control point is three floating-point
values representing x, y, and z. Internal glVertex3()
commands are generated when the map is evaluated.
Each control point is four floating-point values representing
x, y, z, and w. Internal glVertex4() commands are
generated when the map is evaluated. 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. 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.
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. 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. 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. 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. 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.
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.
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().
When the GL_ARB_multitexture extension is supported,
GL_INVALID_OPERATION is generated if glMap1() is called
and the value of GL_ACTIVE_TEXTURE_ARB is not GL_TEXTURE0_ARB.
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
glBegin(3), glColor(3), glEnable(3), glEvalCoord(3), glEvalMesh(3), glEvalPoint(3), glMap2(3), glMapGrid(3),
glNormal(3), glTexCoord(3), glVertex(3)
glMap1(3G)
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