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_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
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_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 fgluNurbsCallback). 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 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.
fgluGetString can be used to determine the GLU version.
SEE ALSO
fgluGetNurbsProperty, fgluLoadSamplingMatrices,
fgluNewNurbsRenderer, fgluGetString, fgluNurbsCallback