fgluNurbsProperty(3G) OpenGL Reference fgluNurbsProperty(3G)NAME
fgluNurbsProperty - set a NURBS property
FORTRAN SPECIFICATION
SUBROUTINE fgluNurbsProperty( CHARACTER*8 nurb,
INTEGER*4 property,
REAL*4 value )
PARAMETERS
nurb Specifies the NURBS object (created with fgluNewNurbsRenderer).
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
fgluNurbsProperty 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 fgluNurbsCallback). 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,
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fgluNurbsProperty(3G) OpenGL Reference fgluNurbsProperty(3G)
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 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 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
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
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fgluNurbsProperty(3G) OpenGL Reference fgluNurbsProperty(3G)
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 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 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
fgluLoadSamplingMatrices 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
fgluLoadSamplingMatrices 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.
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fgluNurbsProperty(3G) OpenGL Reference fgluNurbsProperty(3G)
fgluGetString 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
fgluGetNurbsProperty, fgluLoadSamplingMatrices, fgluNewNurbsRenderer,
fgluGetString, fgluNurbsCallback
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