GLMAP1(3G) GLMAP1(3G)
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 uh, 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, nor-mals, normals,
mals, 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 coordi-nates, coordinates,
nates, 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. (it is really difficult to show this math
in ASCII) Define p ( uh) as
p(u) = Sum(i=0)^(n) ( Bi^n (u)Ri)
where Ri is a control point and Bi^n (u) is the ith Bernstein polynomial of degree n (order = n + 1):
Bi^n(u) = (n,i) u^i (1-u)^(n-i)
Recall that
0^0 == 1 and (n,0) == 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 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)/(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 com-mands. commands.
mands.
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 tex-ture texture
ture 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 com-mands. commands.
mands.
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 com-mands. commands.
mands.
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 com-mands. commands.
mands.
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 cor-responding corresponding
responding 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.
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(3G), glColor(3G), glEnable(3G), glEvalCoord(3G), glEvalMesh(3G), glEvalPoint(3G), glMap2(3G), glMapGrid(3G), glNormal(3G),
glTexCoord(3G), glVertex(3G)
GLMAP1(3G)
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