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 tes-
sellated 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 ini-
tial 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,
surfaces they approximate.
GLU_DOMAIN_DISTANCE allows users to spec-
ify, in parametric coordinates, how many
sample 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
independent, that is, the surface is ren-
dered so that the maximum length, in object
space, of edges of the tessellation poly-
gons 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 ren-
dered in such a way that the value speci-
fied 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 render-
ing 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 value is 0.5.
GLU_U_STEP Specifies the number of sample points per
unit length taken along the u axis in para-
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
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 surface 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 call-
back 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 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 pro-
jection 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 view-
port.
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 func-
tion. This mode is initially set to
GL_TRUE. Changing it from GL_TRUE to
GL_FALSE does not affect the sampling and
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 property are only
available if the GLU version is 1.3 or greater.
SEE ALSO
gluGetNurbsProperty, gluLoadSamplingMatrices,
gluNewNurbsRenderer, gluGetString, gluNurbsCallback
1