NAMEgluNurbsProperty- set a NURBS propertyCSPECIFICATIONvoidgluNurbsProperty( GLUnurbs*nurb, GLenumproperty, GLfloatvalue)PARAMETERSnurbSpecifies the NURBS object (created withgluNewNurbsRenderer).propertySpecifies the property to be set. Valid values areGLU_SAMPLING_TOLERANCE,GLU_DISPLAY_MODE,GLU_CULLING,GLU_AUTO_LOAD_MATRIX,GLU_PARAMETRIC_TOLERANCE,GLU_SAMPLING_METHOD,GLU_U_STEP,GLU_V_STEP, orGLU_NURBS_MODE_EXT.valueSpecifies the value of the indicated property. It may be a numeric value, or one ofGLU_OUTLINE_POLYGON,GLU_FILL,GLU_OUTLINE_PATCH,GL_TRUE,GL_FALSE,GLU_PATH_LENGTH,GLU_PARAMETRIC_ERROR,GLU_DOMAIN_DISTANCE,GLU_NURBS_RENDERER_EXT, orGLU_NURBS_TESSELLATOR_EXT.DESCRIPTIONgluNurbsPropertyis used to control properties stored in a NURBS object. These properties affect the way that a NURBS curve is rendered. The accepted values forpropertyare as follows:GLU_NURBS_MODE_EXTvalueshould be set to be eitherGLU_NURBS_RENDERER_EXTorGLU_NURBS_TESSELLATOR_EXT. When set toGLU_NURBS_RENDERER_EXT, NURBS objects are tessellated into openGL primitives and sent to the pipeline for rendering. When set toGLU_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 (seegluNurbsCallback). This allows the user to cache the tessellated results for further processing.GLU_SAMPLING_METHODSpecifies how a NURBS surface should be tessellated.valuemay be one ofGLU_PATH_LENGTH,GLU_PARAMETRIC_ERROR,GLU_DOMAIN_DISTANCE,GLU_OBJECT_PATH_LENGTH_EXT, orGLU_OBJECT_PARAMETRIC_ERROR_EXT. When set toGLU_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 byGLU_SAMPLING_TOLERANCE.GLU_PARAMETRIC_ERRORspecifies that the surface is rendered in such a way that the value specified byGLU_PARAMETRIC_TOLERANCEdescribes the maximum distance, in pixels, between the tessellation polygons and the surfaces they approximate.GLU_DOMAIN_DISTANCEallows users to specify, in parametric coordinates, how many sample points per unit length are taken inu,vdirection.GLU_OBJECT_PATH_LENGTH_EXTis similar toGLU_PATH_LENGTHexcept 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 byGLU_SAMPLING_TOLERANCE.GLU_OBJECT_PARAMETRIC_ERROR_EXTis similar toGLU_PARAMETRIC_ERRORexcept that it is view independent, that is, the surface is rendered in such a way that the value specified byGLU_PARAMETRIC_TOLERANCEdescribes the maximum distance, in object space, between the tessellation polygons and the surfaces they approximate. The initial value ofGLU_SAMPLING_METHODisGLU_PATH_LENGTH.GLU_SAMPLING_TOLERANCESpecifies the maximum length, in pixels or in object space length unit, to use when the sampling method is set toGLU_PATH_LENGTHorGLU_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_TOLERANCESpecifies the maximum distance, in pixels or in object space length unit, to use when the sampling method isGLU_PARAMETRIC_ERRORorGLU_OBJECT_PARAMETRIC_ERROR_EXT. The initial value is 0.5.GLU_U_STEPSpecifies the number of sample points per unit length taken along theuaxis in parametric coordinates. It is needed whenGLU_SAMPLING_METHODis set toGLU_DOMAIN_DISTANCE. The initial value is 100.GLU_V_STEPSpecifies the number of sample points per unit length taken along thevaxis in parametric coordinate. It is needed whenGLU_SAMPLING_METHODis set toGLU_DOMAIN_DISTANCE. The initial value is 100.GLU_DISPLAY_MODEvaluecan be set toGLU_OUTLINE_POLYGON,GLU_FILL, orGLU_OUTLINE_PATCH. WhenGLU_NURBS_MODE_EXTis set to beGLU_NURBS_RENDERER_EXT,valuedefines how a NURBS surface should be rendered. Whenvalueis set toGLU_FILL, the surface is rendered as a set of polygons. Whenvalueis set toGLU_OUTLINE_POLYGON, the NURBS library draws only the outlines of the polygons created by tessellation. Whenvalueis set toGLU_OUTLINE_PATCHjust the outlines of patches and trim curves defined by the user are drawn. WhenGLU_NURBS_MODE_EXTis set to beGLU_NURBS_TESSELLATOR_EXT,valuedefines how a NURBS surface should be tessellated. WhenGLU_DISPLAY_MODEis set toGLU_FILLorGLU_OUTLINE_POLY, the NURBS surface is tessellated into openGL triangle primitives which can be retrieved back through callback functions. IfGLU_DISPLAY_MODEis set toGLU_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 isGLU_FILL.GLU_CULLINGvalueis a boolean value that, when set toGL_TRUE, indicates that a NURBS curve should be discarded prior to tessellation if its control points lie outside the current viewport. The initial value isGL_FALSE.GLU_AUTO_LOAD_MATRIXvalueis a boolean value. When set toGL_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 toGL_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 thegluLoadSamplingMatricesfunction. This mode is initially set toGL_TRUE. Changing it fromGL_TRUEtoGL_FALSEdoes not affect the sampling and culling matrices untilgluLoadSamplingMatricesis called.NOTESIfGLU_AUTO_LOAD_MATRIXis true, sampling and culling may be executed incorrectly if NURBS routines are compiled into a display list. ApropertyofGLU_PARAMETRIC_TOLERANCE,GLU_SAMPLING_METHOD,GLU_U_STEP, orGLU_V_STEP, or avalueofGLU_PATH_LENGTH,GLU_PARAMETRIC_ERROR,GLU_DOMAIN_DISTANCEare only available if the GLU version is 1.1 or greater. They are not valid parameters in GLU 1.0.gluGetStringcan be used to determine the GLU version.SEEALSOgluGetNurbsProperty,gluLoadSamplingMatrices,gluNewNurbsRenderer,gluGetString,gluNurbsCallback