GLMAP2(3G) GLMAP2(3G)
NAME
glMap2d, glMap2f - define a two-dimensional evaluator
C SPECIFICATION
void glMap2d( GLenum target,
GLdouble u1,
GLdouble u2,
GLint ustride,
GLint uorder,
GLdouble v1,
GLdouble v2,
GLint vstride,
GLint vorder,
const GLdouble *points )
void glMap2f( GLenum target,
GLfloat u1,
GLfloat u2,
GLint ustride,
GLint uorder,
GLfloat v1,
GLfloat v2,
GLint vstride,
GLint vorder,
const GLfloat *points )
PARAMETERS
target Specifies the kind of values that are generated by the evaluator. Symbolic constants
GL_MAP2_VERTEX_3, GL_MAP2_VERTEX_4, GL_MAP2_INDEX, GL_MAP2_COLOR_4, GL_MAP2_NORMAL,
GL_MAP2_TEXTURE_COORD_1, GL_MAP2_TEXTURE_COORD_2, GL_MAP2_TEXTURE_COORD_3, and
GL_MAP2_TEXTURE_COORD_4 are accepted.
u1, u2 Specify a linear mapping of u, as presented to glEvalCoord2, to u hat, one of the two vari-ables variables
ables that are evaluated by the equations specified by this command. Initially, u1 is 0 and
u2 is 1.
ustride Specifies the number of floats or doubles between the beginning of control point Rij and the
beginning of control point R(i+1)j , where i and j are the u and v control point indices,
respectively. 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. The initial value of ustride is 0.
uorder Specifies the dimension of the control point array in the u axis. Must be positive. The
initial value is 1.
v1, v2 Specify a linear mapping of v, as presented to glEvalCoord2, to v hat, one of the two vari-ables variables
ables that are evaluated by the equations specified by this command. Initially, v1 is 0 and
v2 is 1.
vstride Specifies the number of floats or doubles between the beginning of control point Rij and the
beginning of control point Ri(j+1), where i and j are the u and v control point indices,
respectively. 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. The initial value of vstride is 0.
vorder Specifies the dimension of the control point array in the v axis. Must be positive. The
initial value is 1.
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 on 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 surfaces used in
computer graphics, including B-spline surfaces, NURBS surfaces, Bezier surfaces, and so on.
Evaluators define surfaces based on bivariate Bernstein polynomials. Define p ( u hat , v hat ) as
p(u hat, v hat) = Sum(i=0 to n) Sum(j=0 to n) Bi^n (u hat) Bj^m (v hat) Rij
where Rij is a control point, Bi^n(u hat) is the ith Bernstein polynomial of degree
n (uorder = n + 1)
Bi^n ( u hat ) = (n,i) (u hat)^i (1 - u hat) ^ (n-1)
and Bj^m ( v hat ) is the jth Bernstein polynomial of degree m (vorder = m + 1)
Bj^m ( u hat ) = (m,j) (v hat)^j (1 - b hat) ^ (m-j)
Recall that
0^0 == 1 and (0,n) == 1
glMap2 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. When glEvalCoord2 presents values u and v, the
bivariate Bernstein polynomials are evaluated using u hat and v hat, where
u hat = (u-u1)/(u2-u1)
v hat = (v-v1)/(v2-v1)
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_MAP2_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_MAP2_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_MAP2_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_MAP2_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_MAP2_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_MAP2_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_MAP2_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_MAP2_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_MAP2_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.
ustride, uorder, vstride, vorder, 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. There are uorder*vorder con-trol control
trol points in the array. ustride specifies how many float or double locations are skipped to
advance the internal memory pointer from control point Rij to control point R(i+1)j. vstride speci-fies specifies
fies how many float or double locations are skipped to advance the internal memory pointer from con-trol control
trol point Rij to control point Ri(j+1).
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 glMap2 before glMap2 returns. Changes to the contents of points have no effect after
glMap2 is called.
Initially, GL_AUTO_NORMAL is enabled. If GL_AUTO_NORMAL is enabled, normal vectors are generated when
either GL_MAP2_VERTEX_3 or GL_MAP2_VERTEX_4 is used to generate vertices.
ERRORS
GL_INVALID_ENUM is generated if target is not an accepted value.
GL_INVALID_VALUE is generated if u1 is equal to u2, or if v1 is equal to v2.
GL_INVALID_VALUE is generated if either ustride or vstride is less than the number of values in a
control point.
GL_INVALID_VALUE is generated if either uorder or vorder is less than 1 or greater than the return
value of GL_MAX_EVAL_ORDER.
GL_INVALID_OPERATION is generated if glMap2 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 glMap2 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_MAP2_VERTEX_3
glIsEnabled with argument GL_MAP2_VERTEX_4
glIsEnabled with argument GL_MAP2_INDEX
glIsEnabled with argument GL_MAP2_COLOR_4
glIsEnabled with argument GL_MAP2_NORMAL
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_1
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_2
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_3
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_4
SEE ALSO
glBegin(3G), glColor(3G), glEnable(3G), glEvalCoord(3G), glEvalMesh(3G), glEvalPoint(3G), glMap1(3G), glMapGrid(3G), glNormal(3G),
glTexCoord(3G), glVertex(3G)
GLMAP2(3G)
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