GLUNURBSPROPERTY(3G) GLUNURBSPROPERTY(3G)
NAME
gluNurbsProperty - set a NURBS property
C SPECIFICATION
void gluNurbsProperty( GLUnurbs* nurb,
GLenum property,
GLfloat value )
PARAMETERS
nurb Specifies the NURBS object (created with
gluNewNurbsRenderer).
property Specifies the property to be set. Valid values are
GLUSAMPLINGTOLERANCE, GLUDISPLAYMODE, GLUCULING,
GLUAUTOLOADMATRIX, GLUPARAMETRICTOLERANCE,
GLUSAMPLINGMETHOD, GLUSTEP, GLUVSTEP, or
GLUNURBSMODE.
value Specifies the value of the indicated property. It may be a
numeric value, or one of GLUOUTLINEPOLYGON, GLUFIL,
GLUOUTLINEPATCH, GLTRUE, GLFALSE, GLUPATHLENGTH,
GLUPARAMETRICEROR, GLUDOMAINDISTANCE,
GLUNURBSRENDERER, or GLUNURBSTESELATOR.
DESCRIPTION
gluNurbsProperty is used to control properties stored in a NURBS
object. These properties affect the way that a NURBS curve is rendered.
The accepted values for property are as follows:
GLUNURBSMODE value should be set to be either GLUNURBSRENDERER or
GLUNURBSTESELATOR. When set to GLUNURBSRENDERER,
NURBS objects are tessellated into OpenGL primitives and
sent to the pipeline for rendering. When set to
GLUNURBSTESELATOR, NURBS objects are tessellated
into OpenGL primitives but the vertices, normals, col-
ors, and/or textures are retrieved back through a call-
back interface (see gluNurbsCallback). This allows the
user to cache the tessellated results for further pro-
cessing. The initial value is GLUNURBSRENDERER.
GLUSAMPLINGMETHOD
Specifies how a NURBS surface should be tessellated.
value may be one of GLUPATHLENGTH,
GLUPARAMETRICEROR, GLUDOMAINDISTANCE,
GLUOBJECTPATHLENGTH, or GLUOBJECTPARAMETRICEROR.
When set to GLUPATHLENGTH, the surface is rendered so
that the maximum length, in pixels, of the edges of the
tessellation polygons is no greater than what is speci-
fied by GLUSAMPLINGTOLERANCE.
GLUPARAMETRICEROR specifies that the surface is ren-
dered in such a way that the value specified by
GLUPARAMETRICTOLERANCE describes the maximum distance,
in pixels, between the tessellation polygons and the
surfaces they approximate.
GLUDOMAINDISTANCE allows users to specify, in paramet-
ric coordinates, how many sample points per unit length
are taken in u, v direction.
GLUOBJECTPATHLENGTH is similar to GLUPATHLENGTH
except that it is view independent, that is, the surface
is rendered so that the maximum length, in object space,
of edges of the tessellation polygons is no greater than
what is specified by GLUSAMPLINGTOLERANCE.
GLUOBJECTPARAMETRICEROR is similar to
GLUPARAMETRICEROR except that it is view independent,
that is, the surface is rendered in such a way that the
value specified by GLUPARAMETRICTOLERANCE describes
the maximum distance, in object space, between the tes-
sellation polygons and the surfaces they approximate.
The initial value of GLUSAMPLINGMETHOD is
GLUPATHLENGTH.
GLUSAMPLINGTOLERANCE
Specifies the maximum length, in pixels or in object
space length unit, to use when the sampling method is
set to GLUPATHLENGTH or GLUOBJECTPATHLENGTH. The
NURBS code is conservative when rendering a curve or
surface, so the actual length can be somewhat shorter.
The initial value is 50.0 pixels.
GLUPARAMETRICTOLERANCE
Specifies the maximum distance, in pixels or in object
space length unit, to use when the sampling method is
GLUPARAMETRICEROR or GLUOBJECTPARAMETRICEROR.
The initial value is 0.5.
GLUSTEP Specifies the number of sample points per unit length
taken along the u axis in parametric coordinates. It is
needed when GLUSAMPLINGMETHOD is set to
GLUDOMAINDISTANCE. The initial value is 100.
GLUVSTEP Specifies the number of sample points per unit length
taken along the v axis in parametric coordinate. It is
needed when GLUSAMPLINGMETHOD is set to
GLUDOMAINDISTANCE. The initial value is 100.
GLUDISPLAYMODE
value can be set to GLUOUTLINEPOLYGON, GLUFIL, or
GLUOUTLINEPATCH. When GLUNURBSMODE is set to be
GLUNURBSRENDERER, value defines how a NURBS surface
should be rendered. When value is set to GLUFIL, the
surface is rendered as a set of polygons. When value is
set to GLUOUTLINEPOLYGON, the NURBS library draws only
the outlines of the polygons created by tessellation.
When value is set to GLUOUTLINEPATCH just the outlines
of patches and trim curves defined by the user are
drawn.
When GLUNURBSMODE is set to be GLUNURBSTESELATOR,
value defines how a NURBS surface should be tessellated.
When GLUDISPLAYMODE is set to GLUFIL or
GLUOUTLINEPOLYGON, the NURBS surface is tessellated
into OpenGL triangle primitives which can be retrieved
back through callback functions. If GLUDISPLAYMODE is
set to GLUOUTLINEPATCH, only the outlines of the
patches and trim curves are generated as a sequence of
line strips which can be retrieved back through callback
functions.
The initial value is GLUFIL.
GLUCULING value is a boolean value that, when set to GLTRUE,
indicates that a NURBS curve should be discarded prior
to tessellation if its control points lie outside the
current viewport. The initial value is GLFALSE.
GLUAUTOLOADMATRIX
value is a boolean value. When set to GLTRUE, the NURBS
code downloads the projection matrix, the modelview
matrix, and the viewport from the GL 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 the viewport.
If this mode is set to GLFALSE, then the program needs
to provide a projection matrix, a modelview matrix, and
a viewport for the NURBS renderer to use to construct
sampling and culling matrices. This can be done with
the gluLoadSamplingatrices function. This mode is ini-
tially set to GLTRUE. Changing it from GLTRUE to
GLFALSE does not affect the sampling and culling matri-
ces until gluLoadSamplingatrices is called.
NOTES
If GLUAUTOLOADMATRIX is true, sampling and culling may be executed
incorrectly if NURBS routines are compiled into a display list.
A property of GLUPARAMETRICTOLERANCE, GLUSAMPLINGMETHOD,
GLUSTEP, or GLUVSTEP, or a value of GLUPATHLENGTH,
GLUPARAMETRICEROR, GLUDOMAINDISTANCE are only available if the GLU
version is 1.1 or greater. They are not valid parameters in GLU 1.0.
gluGetString can be used to determine the GLU version.
GLUNURBSMODE is only availble if the GLU version is 1.3 or greater.
The GLUOBJECTPATHLENGTH and GLUOBJECTPARAMETRICEROR values for
the GLUSAMPLINGMETHOD property are only available if the GLU version
is 1.3 or greater.
SEE ALSO
gluGetNurbsProperty, gluLoadSamplingatrices, gluNewNurbsRenderer,
gluGetString, gluNurbsCallback
GLUNURBSPROPERTY(3G)
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