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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 GLU_SAMPLING_TOLERANCE,
GLU_DISPLAY_MODE, GLU_CULLING, GLU_AUTO_LOAD_MATRIX, GLU_PARAMETRIC_TOLERANCE,
GLU_SAMPLING_METHOD, GLU_U_STEP, GLU_V_STEP, or GLU_NURBS_MODE.
value Specifies the value of the indicated property. It may be a numeric value, or one of
GLU_OUTLINE_POLYGON, GLU_FILL, GLU_OUTLINE_PATCH, GL_TRUE, GL_FALSE, GLU_PATH_LENGTH,
GLU_PARAMETRIC_ERROR, GLU_DOMAIN_DISTANCE, GLU_NURBS_RENDERER, or GLU_NURBS_TESSELLATOR.
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:
GLU_NURBS_MODE value should be set to be either GLU_NURBS_RENDERER or GLU_NURBS_TESSELLATOR. When set
to GLU_NURBS_RENDERER, NURBS objects are tessellated into OpenGL primitives and sent
to the pipeline for rendering. When set to GLU_NURBS_TESSELLATOR, NURBS objects are
tessellated into OpenGL primitives but the vertices, normals, colors, and/or textures
are retrieved back through a callback interface (see gluNurbsCallback). This allows
the user to cache the tessellated results for further processing. The initial value
is GLU_NURBS_RENDERER.
GLU_SAMPLING_METHOD
Specifies how a NURBS surface should be tessellated. value may be one of
GLU_PATH_LENGTH, GLU_PARAMETRIC_ERROR, GLU_DOMAIN_DISTANCE, GLU_OBJECT_PATH_LENGTH,
or GLU_OBJECT_PARAMETRIC_ERROR. When set to GLU_PATH_LENGTH, the surface is rendered
so that the maximum length, in pixels, of the edges of the tessellation polygons is no
greater than what is specified by GLU_SAMPLING_TOLERANCE.
GLU_PARAMETRIC_ERROR specifies that the surface is rendered in such a way that the
value specified by GLU_PARAMETRIC_TOLERANCE describes the maximum distance, in pixels,
between the tessellation polygons and the surfaces they approximate.
GLU_DOMAIN_DISTANCE allows users to specify, in parametric coordinates, how many sam-ple sample
ple points per unit length are taken in u, v direction.
GLU_OBJECT_PATH_LENGTH is similar to GLU_PATH_LENGTH except that it is view indepen-dent, independent,
dent, 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
GLU_SAMPLING_TOLERANCE.
GLU_OBJECT_PARAMETRIC_ERROR is similar to GLU_PARAMETRIC_ERROR except that it is view
independent, that is, the surface is rendered in such a way that the value specified
by GLU_PARAMETRIC_TOLERANCE describes the maximum distance, in object space, between
the tessellation polygons and the surfaces they approximate.
The initial value of GLU_SAMPLING_METHOD is GLU_PATH_LENGTH.
GLU_SAMPLING_TOLERANCE
Specifies the maximum length, in pixels or in object space length unit, to use when
the sampling method is set to GLU_PATH_LENGTH or GLU_OBJECT_PATH_LENGTH. 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.
GLU_PARAMETRIC_TOLERANCE
Specifies the maximum distance, in pixels or in object space length unit, to use when
the sampling method is GLU_PARAMETRIC_ERROR or GLU_OBJECT_PARAMETRIC_ERROR. The ini-tial initial
tial value is 0.5.
GLU_U_STEP Specifies the number of sample points per unit length taken along the u axis in para-metric parametric
metric coordinates. It is needed when GLU_SAMPLING_METHOD is set to
GLU_DOMAIN_DISTANCE. The initial value is 100.
GLU_V_STEP Specifies the number of sample points per unit length taken along the v axis in para-metric parametric
metric coordinate. It is needed when GLU_SAMPLING_METHOD is set to
GLU_DOMAIN_DISTANCE. The initial value is 100.
GLU_DISPLAY_MODE
value can be set to GLU_OUTLINE_POLYGON, GLU_FILL, or GLU_OUTLINE_PATCH. When
GLU_NURBS_MODE is set to be GLU_NURBS_RENDERER, value defines how a NURBS surface
should be rendered. When value is set to GLU_FILL, the surface is rendered as a set
of polygons. When value is set to GLU_OUTLINE_POLYGON, the NURBS library draws only
the outlines of the polygons created by tessellation. When value is set to
GLU_OUTLINE_PATCH just the outlines of patches and trim curves defined by the user are
drawn.
When GLU_NURBS_MODE is set to be GLU_NURBS_TESSELLATOR, value defines how a NURBS sur-face surface
face should be tessellated. When GLU_DISPLAY_MODE is set to GLU_FILL or
GLU_OUTLINE_POLYGON, the NURBS surface is tessellated into OpenGL triangle primitives
which can be retrieved back through callback functions. If GLU_DISPLAY_MODE is set to
GLU_OUTLINE_PATCH, 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 GLU_FILL.
GLU_CULLING value is a boolean value that, when set to GL_TRUE, indicates that a NURBS curve
should be discarded prior to tessellation if its control points lie outside the cur-rent current
rent viewport. The initial value is GL_FALSE.
GLU_AUTO_LOAD_MATRIX
value is a boolean value. When set to GL_TRUE, 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 seg-ments segments
ments or polygons and to cull a NURBS surface if it lies outside the viewport.
If this mode is set to GL_FALSE, 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 gluLoadSamplingMatrices
function. This mode is initially set to GL_TRUE. Changing it from GL_TRUE to
GL_FALSE does not affect the sampling and culling matrices until
gluLoadSamplingMatrices is called.
NOTES
If GLU_AUTO_LOAD_MATRIX is true, sampling and culling may be executed incorrectly if NURBS routines
are compiled into a display list.
A property of GLU_PARAMETRIC_TOLERANCE, GLU_SAMPLING_METHOD, GLU_U_STEP, or GLU_V_STEP, or a value of
GLU_PATH_LENGTH, GLU_PARAMETRIC_ERROR, GLU_DOMAIN_DISTANCE 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.
GLU_NURBS_MODE is only availble if the GLU version is 1.3 or greater.
The GLU_OBJECT_PATH_LENGTH and GLU_OBJECT_PARAMETRIC_ERROR values for the GLU_SAMPLING_METHOD prop-erty property
erty are only available if the GLU version is 1.3 or greater.
SEE ALSO
gluGetNurbsProperty(3G), gluLoadSamplingMatrices(3G), gluNewNurbsRenderer(3G), gluGetString(3G), gluNurbsCallback(3G)
GLUNURBSPROPERTY(3G)
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