fglMap1(3G) OpenGL Reference fglMap1(3G)NAME
fglMap1d, fglMap1f - define a one-dimensional evaluator
FORTRAN SPECIFICATION
SUBROUTINE fglMap1d( INTEGER*4 target,
REAL*4 u1,
REAL*4 u2,
INTEGER*4 stride,
INTEGER*4 order,
CHARACTER*8 points )
SUBROUTINE fglMap1f( INTEGER*4 target,
REAL*4 u1,
REAL*4 u2,
INTEGER*4 stride,
INTEGER*4 order,
CHARACTER*8 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 fglEvalCoord1, to
^, 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 fglVertex, fglNormal,
fglTexCoord, and fglColor commands, except that the generated values do
not update the current normal, texture coordinates, or color.
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fglMap1(3G) OpenGL Reference fglMap1(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:
B-splines, Bezier curves, Hermite splines, and so on.
Evaluators define curves based on Bernstein polynomials. Define p(^) as
n
R n
p(^) = B (^)R
i=0 i i
n
where R is a control point and B (^) is the ith Bernstein polynomial of
i i
degree n (order = n + 1):
( )
n n i n-i
B (^) = | |^ (1-^)
i
(i )
Recall that
( )
0 n
0 = 1 and | | = 1
( 0 )
fglMap1 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
fglEnable and fglDisable with the map name, one of the nine predefined
values for target described below. fglEvalCoord1 evaluates the one-
dimensional maps that are enabled. When fglEvalCoord1 presents a value
u, the Bernstein functions are evaluated using ^, where
_______
^ =
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
fglVertex3 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
fglVertex4 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
fglIndex commands are generated when the map is
evaluated but the current index is not updated
with the value of these fglIndex commands.
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fglMap1(3G) OpenGL Reference fglMap1(3G)
GL_MAP1_COLOR_4 Each control point is four floating-point values
representing red, green, blue, and alpha.
Internal fglColor4 commands are generated when
the map is evaluated but the current color is
not updated with the value of these fglColor4
commands.
GL_MAP1_NORMAL Each control point is three floating-point
values representing the x, y, and z components
of a normal vector. Internal fglNormal commands
are generated when the map is evaluated but the
current normal is not updated with the value of
these fglNormal commands.
GL_MAP1_TEXTURE_COORD_1 Each control point is a single floating-point
value representing the s texture coordinate.
Internal fglTexCoord1 commands are generated
when the map is evaluated but the current
texture coordinates are not updated with the
value of these fglTexCoord commands.
GL_MAP1_TEXTURE_COORD_2 Each control point is two floating-point values
representing the s and t texture coordinates.
Internal fglTexCoord2 commands are generated
when the map is evaluated but the current
texture coordinates are not updated with the
value of these fglTexCoord commands.
GL_MAP1_TEXTURE_COORD_3 Each control point is three floating-point
values representing the s, t, and r texture
coordinates. Internal fglTexCoord3 commands are
generated when the map is evaluated but the
current texture coordinates are not updated with
the value of these fglTexCoord commands.
GL_MAP1_TEXTURE_COORD_4 Each control point is four floating-point values
representing the s, t, r, and q texture
coordinates. Internal fglTexCoord4 commands are
generated when the map is evaluated but the
current texture coordinates are not updated with
the value of these fglTexCoord 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.
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fglMap1(3G) OpenGL Reference fglMap1(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 fglMap1 before fglMap1
returns. Changes to the contents of points have no effect after fglMap1
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 fglMap1 is executed between the
execution of fglBegin and the corresponding execution of fglEnd.
ASSOCIATED GETS
fglGetMap
fglGet with argument GL_MAX_EVAL_ORDER
fglIsEnabled with argument GL_MAP1_VERTEX_3
fglIsEnabled with argument GL_MAP1_VERTEX_4
fglIsEnabled with argument GL_MAP1_INDEX
fglIsEnabled with argument GL_MAP1_COLOR_4
fglIsEnabled with argument GL_MAP1_NORMAL
fglIsEnabled with argument GL_MAP1_TEXTURE_COORD_1
fglIsEnabled with argument GL_MAP1_TEXTURE_COORD_2
fglIsEnabled with argument GL_MAP1_TEXTURE_COORD_3
fglIsEnabled with argument GL_MAP1_TEXTURE_COORD_4
SEE ALSO
fglBegin, fglColor, fglEnable, fglEvalCoord, fglEvalMesh, fglEvalPoint,
fglMap2, fglMapGrid, fglNormal, fglTexCoord, fglVertex
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