gluNurbsProperty
[New
- Windows 95, OEM Service Release 2]
The gluNurbsProperty function sets a NURBS
property.
void gluNurbsProperty(
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GLUnurbsObj * nobj, |
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GLenum property,
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GLfloat value |
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); |
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Parameters
nobj
The NURBS object
(created with gluNewNurbsRenderer).
property
The property
to be set. The following values are valid: GLU_SAMPLING_TOLERANCE,
GLU_DISPLAY_MODE, GLU_CULLING, GLU_AUTO_LOAD_MATRIX, GLU_PARAMETRIC_TOLERANCE,
GLU_SAMPLING_METHOD, GLU_U_STEP, and GLU_V_STEP. For the meaning of these
values, see the following Remarks section.
value
The value to
which to set the indicated property. The value parameter can be a
numeric value or one of the following three values: GLU_PATH_LENGTH,
GLU_PARAMETRIC_ERROR, or GLU_DOMAIN_DISTANCE. For the meaning of these values,
see the following Remarks section.
Remarks
Use gluNurbsProperty to control properties stored
in a NURBS object. These properties affect the way a NURBS curve is rendered.
The valid values for property are as follows:
GLU_SAMPLING_TOLERANCE
Specifies the
maximum length, in pixels, to use when the sampling method is set to
GLU_PATH_LENGTH. The default value is 50.0 pixels.
GLU_DISPLAY_MODE
The value
parameter defines how a NURBS surface is to be rendered. You can set value
to GLU_FILL, GLU_OUTLINE_POLYGON, or GLU_OUTLINE_PATCH. The following table
describes the results of these constants.
|
Constant |
Result |
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GLU_FILL |
The surface
is rendered as a set of polygons. This is the default value. |
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GLU_OUTLINE_POLYGON
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The NURBS
library draws only the outlines of the polygons created by tessellation. |
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GLU_OUTLINE_PATCH
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Only the
outlines of patches and trim curves defined by the user are drawn. |
GLU_CULLING
The value
parameter is a Boolean value. When value is set to GL_TRUE, NURBS curves
whose control points lie outside the current viewport are discarded prior to
tessellation. The default is GL_FALSE (because a NURBS curve cannot fall
entirely within the convex hull of its control points).
GLU_PARAMETRIC_TOLERANCE
Specifies the
maximum distance, in pixels, to use when the sampling method is set to
GLU_PARAMETRIC_ERROR. The default value is 0.5.
GLU_SAMPLING_METHOD
Specifies how
to tessallate a NURBS surface. GLU_SAMPLING_METHOD can have one of the
following three values.
|
Value |
Meaning |
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GLU_PATH_LENGTH |
The default
value. Specifies that surfaces rendered with the maximum length, in pixels,
of the edges of the tessellation polygons are no greater than the value
specified by GLU_SAMPLING_TOLERANCE. |
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GLU_PARAMETRIC_ERROR |
Specifies
that in rendering the surface, the value of GLU_PARAMETRIC_TOLERANCE
specifies the maximum distance, in pixels, between the tessellation polygons
and the surfaces they approximate. |
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GLU_DOMAIN_DISTANCE |
Specifies,
in parametric coordinates, how many sample points per unit length to take in
the u and v dimensions. |
GLU_U_STEP
Specifies the
number of sample points per unit length taken along the u dimension in
parametric coordinates. The value of GLU_U_STEP is used when
GLU_SAMPLING_METHOD is set to GLU_DOMAIN_DISTANCE. The default value is 100.
GLU_V_STEP
Specifies the
number of sample points per unit length taken along the v dimension in
parametric coordinates. The value of GLU_V_STEP is used when
GLU_SAMPLING_METHOD is set to GLU_DOMAIN_DISTANCE. The default value is 100.
GLU_AUTO_LOAD_MATRIX
The value
parameter is a Boolean value. When set to GL_TRUE, the NURBS code downloads the
projection matrix, modelview matrix, and viewport from the OpenGL server to
compute sampling and culling matrices for each NURBS curve that is rendered.
Sampling and culling matrices are required to determine the tessellation of a
NURBS surface into line segments or polygons and to cull a NURBS surface if it
lies outside of the viewport. If this mode is set to GL_FALSE, you must provide
a projection matrix, modelview matrix, and viewport for the NURBS renderer to
use to construct sampling and culling matrices. You can do this with the gluLoadSamplingMatrices function. The default for
this mode is GL_TRUE. Changing this mode from GL_TRUE to GL_FALSE does not
affect the sampling and culling matrices until you call gluLoadSamplingMatrices.
Note The following property
parameters are supported in GLU version 1.1 or later and are not valid for GLU
version 1.0:
GLU_PARAMETRIC_TOLERANCE,
GLU_SAMPLING_METHOD, GLU_U_STEP, and GLU_V_STEP.
The following
value parameters are supported in GLU version 1.1 or later and are not
valid for GLU version 1.0:
GLU_PATH_LENGTH,
GLU_PARAMETRIC_ERROR, and GLU_DOMAIN_DISTANCE.
See Also
gluGetNurbsProperty, gluGetString, gluLoadSamplingMatrices, gluNewNurbsRenderer