gluNurbsProperty
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 ren-
dered. 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, 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 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 speci-
fied by GLU_SAMPLING_TOLERANCE.
GLU_PARAMETRIC_ERROR specifies that the surface is ren-
dered in such a way that the value specified by
GLU_PARAMETRIC_TOLERANCE describes the maximum dis-
tance, in pixels, between the tessellation polygons and
the surfaces they approximate.
GLU_DOMAIN_DISTANCE allows users to specify, in para-
metric 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 sur-
face 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 indepen-
dent, 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 initial value is 0.5.
GLU_U_STEP Specifies the number of sample points per unit length
taken along the u axis in parametric 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 parametric 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 tessella-
tion. 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 tessel-
lated. 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 call-
back 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
current 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 mod-
elview 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 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 property 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)
