GLUNURBSPROPERTY() GLUNURBSPROPERTY() NAME gluNurbsProperty - set a NURBS property C SPECIFICATION void gluNurbsProperty( GLUnurbs* nurb, GLenum property, GLfloat value ) delim $$ PARAMETERS nurb Specifies the NURBS object (created with gluNewNurbsRenderer). property Specifies the property to be set. Valid values are GLU_SAM- PLING_TOLERANCE, GLU_DISPLAY_MODE, GLU_CULLING, GLU_AUTO_LOAD_MA- TRIX, 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 nu- meric value, or one of GLU_OUTLINE_POLYGON, GLU_FILL, GLU_OUT- LINE_PATCH, GL_TRUE, GL_FALSE, GLU_PATH_LENGTH, GLU_PARAMET- RIC_ERROR, GLU_DOMAIN_DISTANCE, GLU_NURBS_RENDERER_EXT, or GLU_NURBS_TESSELLATOR_EXT. DESCRIPTION gluNurbsProperty is used to control properties stored in a NURBS object. These properties affect the way that a NURBS curve is rendered. The ac- cepted 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_REN- DERER_EXT, NURBS objects are tessellated into openGL primi- tives 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 inter- face (see gluNurbsCallback). 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_OB- JECT_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_PARAMET- RIC_TOLERANCE describes the maximum distance, in pixels, be- tween the tessellation polygons and the surfaces they ap- proximate. 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_PARAMET- RIC_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_PARAMET- RIC_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 ini- tial 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 sur- face is rendered as a set of polygons. When value is set to GLU_OUTLINE_POLYGON, the NURBS library draws only the out- lines 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_TESSELLA- TOR_EXT, value defines how a NURBS surface should be tessel- lated. When GLU_DISPLAY_MODE is set to GLU_FILL or GLU_OUT- LINE_POLY, the NURBS surface is tessellated into openGL tri- angle primitives which can be retrieved back through call- back functions. If GLU_DISPLAY_MODE is set to GLU_OUT- LINE_PATCH, only the outlines of the patches and trim curves are generated as a sequence of line strips which can be re- trieved back through callback functions. The initial value is GLU_FILL. GLU_CULLING value is a boolean value that, when set to GL_TRUE, indi- cates that a NURBS curve should be discarded prior to tes- sellation 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. Sam- pling and culling matrices are required to determine the tessellation of a NURBS surface into line segments or poly- gons 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 view- port for the NURBS renderer to use to construct sampling and culling matrices. This can be done with the gluLoadSam- plingMatrices function. This mode is initially set to GL_TRUE. Changing it from GL_TRUE to GL_FALSE does not af- fect the sampling and culling matrices until gluLoadSam- plingMatrices is called. NOTES If GLU_AUTO_LOAD_MATRIX is true, sampling and culling may be executed in- correctly 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_DO- MAIN_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. SEE ALSO gluGetNurbsProperty, gluLoadSamplingMatrices, gluNewNurbsRenderer, gluGet- String, gluNurbsCallback GLUNURBSPROPERTY()
NAME | C SPECIFICATION | PARAMETERS | DESCRIPTION | NOTES | SEE ALSO
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