gluNurbsProperty

gluNurbsProperty: set a NURBS property.

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, or GLU_V_STEP.
value: Specifies the value of the indicated property. It may be a numeric value, or one of GLU_PATH_LENGTH, GLU_PARAMETRIC_ERROR, or GLU_DOMAIN_DISTANCE.

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_SAMPLING_METHOD: Specifies how a NURBS surface should be tessellated. value may be one of GLU_PATH_LENGTH, GLU_PARAMETRIC_ERROR, or GLU_DOMAIN_DISTANCE. 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. The initial value of GLU_SAMPLING_METHOD is GLU_PATH_LENGTH.
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_SAMPLING_TOLERANCE: Specifies the maximum length, in pixels to use when the sampling method is set to GLU_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, to use when the sampling method is GLU_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 defines how a NURBS surface should be rendered. value can be set to GLU_OUTLINE_POLYGON, GLU_FILL, or GLU_OUTLINE_PATCH. 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. 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 tesselation 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.