

 
Manual Reference Pages  GLUNURBSPROPERTY (3)
NAME
gluNurbsProperty  set a NURBS property
CONTENTS
C Specification
Parameters
Description
Notes
See Also
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_EXT.

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_EXT, or
GLU_NURBS_TESSELLATOR_EXT.


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_EXT
 
value should be set to be either GLU_NURBS_RENDERER_EXT or
GLU_NURBS_TESSELLATOR_EXT. When set to GLU_NURBS_RENDERER_EXT, NURBS objects
are tessellated into openGL primitives and sent to the pipeline for
rendering. When set to GLU_NURBS_TESSELLATOR_EXT, 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.

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_EXT, or
GLU_OBJECT_PARAMETRIC_ERROR_EXT.
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 sample points per unit length are taken in u, v
direction.


GLU_OBJECT_PATH_LENGTH_EXT is similar to GLU_PATH_LENGTH
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 GLU_SAMPLING_TOLERANCE.


GLU_OBJECT_PARAMETRIC_ERROR_EXT 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_EXT.
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_EXT.
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_EXT is set to be GLU_NURBS_RENDERER_EXT,
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_EXT is set to be GLU_NURBS_TESSELLATOR_EXT,
value defines how a NURBS surface should be tessellated.
When GLU_DISPLAY_MODE is set to GLU_FILL or GLU_OUTLINE_POLY,
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 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 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 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.
SEE ALSO
gluGetNurbsProperty,
gluLoadSamplingMatrices,
gluNewNurbsRenderer,
gluGetString,
gluNurbsCallback
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