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, GLU_TRUE, GLU_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 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 gluNurbsCallback()). 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, 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 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 that 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 that can be retrieved back through callback functions.

    The initial value is GLU_FILL.

GLU_CULLING
    value is a boolean value that, when set to GLU_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 GLU_FALSE.

GLU_AUTO_LOAD_MATRIX
    value is a boolean value. When set to GLU_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 GLU_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 GLU_TRUE. Changing it from GLU_TRUE to GLU_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 available 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(), gluGetString(), gluLoadSamplingMatrices(), gluNewNurbsRenderer(), gluNurbsCallback()

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.