glMap1(3G)glMap1(3G)NAME
glMap1, glMap1d, glMap1f - define a one-dimensional evaluator
SYNOPSIS
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
Specifies the kind of values that are generated by the evaluator. Sym‐
bolic 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_TEX‐
TURE_COORD_2, GL_MAP1_TEXTURE_COORD_3, and GL_MAP1_TEXTURE_COORD_4 are
accepted. Specify a linear mapping of u, as presented to glEvalCo‐
ord1(), to u hat, the variable that is evaluated by the equations spec‐
ified 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 con‐
trol points to be embedded in arbitrary data structures. The only con‐
straint 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.
DESCRIPTION
Evaluators provide a way to use polynomial or rational polynomial map‐
ping to produce vertices, normals, texture coordinates, and colors. The
values produced by an evaluator are sent to further stages of GL pro‐
cessing just as if they had been presented using glVertex(), glNor‐
mal(), 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 ( 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 Bern‐
stein 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 call‐
ing glEnable() and glDisable() with the map name, one of the nine pre‐
defined 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 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 repre‐
senting 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 float‐
ing-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() com‐
mands. 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 con‐
trol 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 val‐
ues 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 con‐
trol points in the array. stride specifies how many float or double
locations to advance the internal memory pointer to reach the next con‐
trol 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 val‐
ues 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_OPERA‐
TION is generated if glMap1() is called and the value of GL_ACTIVE_TEX‐
TURE_ARB is not GL_TEXTURE0_ARB.
ASSOCIATED GETSglGetMap()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 ALSOglBegin(3), glColor(3), glEnable(3), glEvalCoord(3), glEvalMesh(3),
glEvalPoint(3), glMap2(3), glMapGrid(3), glNormal(3), glTexCoord(3),
glVertex(3)glMap1(3G)