glMap1(3G) OpenGL Reference 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 GLMAP1VERTEX3, GLMAP1VERTEX4,
GLMAP1INDEX, GLMAP1COLOR4, GLMAP1NORMAL,
GLMAP1TEXTURECOORD1, GLMAP1TEXTURECOORD2,
GLMAP1TEXTURECOORD3, and GLMAP1TEXTURECOORD4 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.
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glMap1(3G) OpenGL Reference glMap1(3G)
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
n
p(u') = sum from i=0 to n B (u') * R
i i
n
where R is a control point and B (u') is the ith Bernstein polynomial of
i i
degree n (order = n+1):
( )
n n i n-i
B (u') = | |u' (1-u')
i
(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 u', where
u' = (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:
GLMAP1VERTEX3 Each control point is three floating-point
values representing x, y, and z. Internal
glVertex3 commands are generated when the map is
evaluated.
GLMAP1VERTEX4 Each control point is four floating-point values
representing x, y, z, and w. Internal glVertex4
commands are generated when the map is
evaluated.
GLMAP1INDEX 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,
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glMap1(3G) OpenGL Reference glMap1(3G)
however.
GLMAP1COLOR4 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.
GLMAP1NORMAL 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.
GLMAP1TEXTURECOORD1 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.
GLMAP1TEXTURECOORD2 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.
GLMAP1TEXTURECOORD3 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.
GLMAP1TEXTURECOORD4 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. 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.
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glMap1(3G) OpenGL Reference glMap1(3G)
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
GLINVALIDENUM is generated if target is not an accepted value.
GLINVALIDVALUE is generated if u1 is equal to u2.
GLINVALIDVALUE is generated if stride is less than the number of values
in a control point.
GLINVALIDVALUE is generated if order is less than one or greater than
GLMAXEVALORDER.
GLINVALIDOPERATION is generated if glMap1 is executed between the
execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGetMap
glGet with argument GLMAXEVALORDER
glIsEnabled with argument GLMAP1VERTEX3
glIsEnabled with argument GLMAP1VERTEX4
glIsEnabled with argument GLMAP1INDEX
glIsEnabled with argument GLMAP1COLOR4
glIsEnabled with argument GLMAP1NORMAL
glIsEnabled with argument GLMAP1TEXTURECOORD1
glIsEnabled with argument GLMAP1TEXTURECOORD2
glIsEnabled with argument GLMAP1TEXTURECOORD3
glIsEnabled with argument GLMAP1TEXTURECOORD4
SEE ALSO
glBegin, glColor, glEnable, glEvalCoord, glEvalMesh, glEvalPoint, glMap2,
glMapGrid, glNormal, glTexCoord, glVertex
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