gluNurbsProperty - set a NURBS property

void gluNurbsProperty( GLUnurbsObj *nobj, GLenumproperty, GLfloatvalue)

nobjSpecifies the NURBS object (created with gluNewNurbsRenderer).propertySpecifies 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.valueSpecifies 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.

gluNurbsProperty is used to control properties stored in a NURBS object. These properties affect the way that a NURBS curve is rendered. The legal values forpropertyare as follows: GLU_SAMPLING_METHOD specifies how a NURBS surface should be tessellated.valuemay be set to 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. 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. The default value of GLU_SAMPLING_METHOD is GLU_PATH_LENGTH. 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 default value is 50.0 pixels. GLU_PARAMETRIC_TOLERANCE specifies the maximum distance, in pixels, to use when the sampling method is set to GLU_PARAMETRIC_ERROR. The default value for GLU_PARAMETRIC_TOLERANCE 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 default 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 default value is 100. GLU_DISPLAY_MODEvaluedefines how a NURBS surface should be rendered.valuecan be set to GLU_FILL, GLU_OUTLINE_POLYGON, or GLU_OUTLINE_PATCH. When set to GLU_FILL, the surface is rendered as a set of polygons. GLU_OUTLINE_POLYGON instructs the NURBS library to draw only the outlines of the polygons created by tessellation. GLU_OUTLINE_PATCH causes just the outlines of patches and trim curves defined by the user to be drawn. The default value is GLU_FILL. GLU_CULLINGvalueis 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 default is GL_FALSE (because a NURBS curve cannot fall entirely within the convex hull of its control points). GLU_AUTO_LOAD_MATRIXvalueis a Boolean value. When set to GL_TRUE, the NURBS code downloads the projection matrix, the modelview matrix, and the viewport from the OpenGL 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 of the viewport. If this mode is set to GL_FALSE, then the user 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. The default for this mode is GL_TRUE. Changing this mode from GL_TRUE to GL_FALSE does not affect the sampling and culling matrices until gluLoadSamplingMatrices is called.

Apropertyof GLU_PARAMETRIC_TOLERANCE, GLU_SAMPLING_METHOD, GLU_U_STEP, or GLU_V_STEP, or avalueof GLU_PATH_LENGTH, GLU_PARAMETRIC_ERROR, GLU_DOMAIN_DISTANCE will only be supported in GLU version number 1.1. They are not valid parameters in GLU 1.0. gluGetString can be used to determine the GLU version.

gluGetNurbsProperty, gluLoadSamplingMatrices, gluNewNurbsRenderer, gluGetString.

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Fri Dec 6 11:18:03 EST 1996
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