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<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>gluNurbsProperty</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="gluNurbsProperty"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gluNurbsProperty — set a NURBS property</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">gluNurbsProperty</b>(</code></td><td>GLUnurbs*  </td><td><var class="pdparam">nurb</var>, </td></tr><tr><td> </td><td>GLenum  </td><td><var class="pdparam">property</var>, </td></tr><tr><td> </td><td>GLfloat  </td><td><var class="pdparam">value</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>nurb</code></em></span></dt><dd><p>
                    Specifies the NURBS object (created with <a class="citerefentry" href="gluNewNurbsRenderer.xml"><span class="citerefentry"><span class="refentrytitle">gluNewNurbsRenderer</span></span></a>).
                </p></dd><dt><span class="term"><em class="parameter"><code>property</code></em></span></dt><dd><p>
                    Specifies the property to be set. Valid values are
                    <code class="constant">GLU_SAMPLING_TOLERANCE</code>,
                    <code class="constant">GLU_DISPLAY_MODE</code>, 
                    <code class="constant">GLU_CULLING</code>,
                    <code class="constant">GLU_AUTO_LOAD_MATRIX</code>,
                    <code class="constant">GLU_PARAMETRIC_TOLERANCE</code>,
                    <code class="constant">GLU_SAMPLING_METHOD</code>,
                    <code class="constant">GLU_U_STEP</code>,
                    <code class="constant">GLU_V_STEP</code>, or
                    <code class="constant">GLU_NURBS_MODE</code>.
                </p></dd><dt><span class="term"><em class="parameter"><code>value</code></em></span></dt><dd><p>
                    Specifies the value of the indicated property.
                    It may be a numeric value or one of 
                    <code class="constant">GLU_OUTLINE_POLYGON</code>,
                    <code class="constant">GLU_FILL</code>,
                    <code class="constant">GLU_OUTLINE_PATCH</code>,
                    <code class="constant">GLU_TRUE</code>,
                    <code class="constant">GLU_FALSE</code>,
                    <code class="constant">GLU_PATH_LENGTH</code>,
                    <code class="constant">GLU_PARAMETRIC_ERROR</code>,
                    <code class="constant">GLU_DOMAIN_DISTANCE</code>,
                    <code class="constant">GLU_NURBS_RENDERER</code>, or
                    <code class="constant">GLU_NURBS_TESSELLATOR</code>.
                </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            <code class="function">gluNurbsProperty</code> 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 <em class="parameter"><code>property</code></em> are as follows:
        </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GLU_NURBS_MODE</code></span></dt><dd><p>
                        <em class="parameter"><code>value</code></em> should be set to be either <code class="constant">GLU_NURBS_RENDERER</code> or
                        <code class="constant">GLU_NURBS_TESSELLATOR</code>. When set to <code class="constant">GLU_NURBS_RENDERER</code>, NURBS objects
                        are tessellated into OpenGL primitives and sent to the pipeline for
                        rendering. When set to <code class="constant">GLU_NURBS_TESSELLATOR</code>, NURBS objects are
                        tessellated into OpenGL primitives but the vertices, normals, colors, and/or textures are 
                        retrieved back through a callback interface (see <a class="citerefentry" href="gluNurbsCallback.xml"><span class="citerefentry"><span class="refentrytitle">gluNurbsCallback</span></span></a>). This allows the user to cache the
                        tessellated results for further processing.
                        The initial value is <code class="constant">GLU_NURBS_RENDERER</code>.
                    </p></dd><dt><span class="term"><code class="constant">GLU_SAMPLING_METHOD</code> </span></dt><dd><p>
                        Specifies how a NURBS surface should be
                        tessellated.
                        <em class="parameter"><code>value</code></em> may be one of <code class="constant">GLU_PATH_LENGTH</code>,
                        <code class="constant">GLU_PARAMETRIC_ERROR</code>,  <code class="constant">GLU_DOMAIN_DISTANCE</code>,
                        <code class="constant">GLU_OBJECT_PATH_LENGTH</code>, or
                        <code class="constant">GLU_OBJECT_PARAMETRIC_ERROR</code>.
                        When set to <code class="constant">GLU_PATH_LENGTH</code>, 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 <code class="constant">GLU_SAMPLING_TOLERANCE</code>. 
                    </p><p>
                        <code class="constant">GLU_PARAMETRIC_ERROR</code> specifies that the surface is rendered in such a 
                        way that the value specified by <code class="constant">GLU_PARAMETRIC_TOLERANCE</code> describes the 
                        maximum distance, in pixels, between the tessellation polygons and the
                        surfaces they approximate. 
                    </p><p>
                        <code class="constant">GLU_DOMAIN_DISTANCE</code> allows users to specify, in parametric coordinates,
                        how many sample points per unit length are taken in <span class="emphasis"><em>u</em></span>, <span class="emphasis"><em>v</em></span>
                        direction.
                    </p><p>
                        <code class="constant">GLU_OBJECT_PATH_LENGTH</code>  is similar to <code class="constant">GLU_PATH_LENGTH</code>
                        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 <code class="constant">GLU_SAMPLING_TOLERANCE</code>.
                    </p><p>
                        <code class="constant">GLU_OBJECT_PARAMETRIC_ERROR</code> is similar to  <code class="constant">GLU_PARAMETRIC_ERROR</code> except that it is view independent; that is, the surface is rendered in such a way that the value specified by <code class="constant">GLU_PARAMETRIC_TOLERANCE</code> describes the maximum distance, in object space, between the tessellation polygons and the surfaces they approximate.
                    </p><p>
                        The initial value of <code class="constant">GLU_SAMPLING_METHOD</code> is <code class="constant">GLU_PATH_LENGTH</code>.
                    </p></dd><dt><span class="term"><code class="constant">GLU_SAMPLING_TOLERANCE</code></span></dt><dd><p>
                        Specifies the maximum length, in pixels or in object space length unit,
                        to use when the sampling method is set to <code class="constant">GLU_PATH_LENGTH</code> or
                        <code class="constant">GLU_OBJECT_PATH_LENGTH</code>.
                        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. 
                    </p></dd><dt><span class="term"><code class="constant">GLU_PARAMETRIC_TOLERANCE</code></span></dt><dd><p>
                        Specifies the maximum distance, in pixels or in object space length unit,
                        to use when the sampling method is <code class="constant">GLU_PARAMETRIC_ERROR</code> or
                        <code class="constant">GLU_OBJECT_PARAMETRIC_ERROR</code>.
                        The initial value is 0.5.
                    </p></dd><dt><span class="term"><code class="constant">GLU_U_STEP</code></span></dt><dd><p>
                        Specifies the number of sample points per unit length taken
                        along the <span class="emphasis"><em>u</em></span> axis in parametric coordinates. It is needed when
                        <code class="constant">GLU_SAMPLING_METHOD</code> is set to <code class="constant">GLU_DOMAIN_DISTANCE</code>.
                        The initial value is 100.
                    </p></dd><dt><span class="term"><code class="constant">GLU_V_STEP</code></span></dt><dd><p>
                        Specifies the number of sample points per unit length taken
                        along the <span class="emphasis"><em>v</em></span> axis in parametric coordinate. It is needed when
                        <code class="constant">GLU_SAMPLING_METHOD</code> is set to <code class="constant">GLU_DOMAIN_DISTANCE</code>. The initial 
                        value is 100.
                    </p></dd><dt><span class="term"><code class="constant">GLU_DISPLAY_MODE</code></span></dt><dd><p>
                        <em class="parameter"><code>value</code></em> can be set to
                        <code class="constant">GLU_OUTLINE_POLYGON</code>, <code class="constant">GLU_FILL</code>, or 
                        <code class="constant">GLU_OUTLINE_PATCH</code>.
                        When <code class="constant">GLU_NURBS_MODE</code> is set to be <code class="constant">GLU_NURBS_RENDERER</code>,
                        <em class="parameter"><code>value</code></em> defines how a NURBS surface should be rendered.
                        When <em class="parameter"><code>value</code></em> is set to <code class="constant">GLU_FILL</code>, the surface is rendered as a
                        set of polygons. When <em class="parameter"><code>value</code></em> is set to
                        <code class="constant">GLU_OUTLINE_POLYGON</code>, the NURBS library draws only the outlines
                        of the polygons created by tessellation. When <em class="parameter"><code>value</code></em> is set to
                        <code class="constant">GLU_OUTLINE_PATCH</code> just the outlines of patches and trim 
                        curves defined by the user are drawn.
                    </p><p>
                        When <code class="constant">GLU_NURBS_MODE</code> is set to be <code class="constant">GLU_NURBS_TESSELLATOR</code>,
                        <em class="parameter"><code>value</code></em> defines how a NURBS surface should be tessellated.
                        When <code class="constant">GLU_DISPLAY_MODE</code> is set to <code class="constant">GLU_FILL</code> or
                        <code class="constant">GLU_OUTLINE_POLYGON</code>, 
                        the NURBS surface is tessellated into OpenGL triangle primitives that can be
                        retrieved back  through callback functions. If <code class="constant">GLU_DISPLAY_MODE</code> is set to 
                        <code class="constant">GLU_OUTLINE_PATCH</code>, 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.
                    </p><p>
                        The initial value is <code class="constant">GLU_FILL</code>.
                    </p></dd><dt><span class="term"><code class="constant">GLU_CULLING</code></span></dt><dd><p>
                        <em class="parameter"><code>value</code></em> is a boolean value that, when set to <code class="constant">GLU_TRUE</code>, indicates that 
                        a NURBS curve should be discarded prior to tessellation if its control points
                        lie outside the current viewport. The initial value is <code class="constant">GLU_FALSE</code>.
                    </p></dd><dt><span class="term"><code class="constant">GLU_AUTO_LOAD_MATRIX</code></span></dt><dd><p>
                        <em class="parameter"><code>value</code></em> is a boolean value. When set to <code class="constant">GLU_TRUE</code>, 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.
                    </p><p>
                        If this mode is set to <code class="constant">GLU_FALSE</code>, 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 <a class="citerefentry" href="gluLoadSamplingMatrices.xml"><span class="citerefentry"><span class="refentrytitle">gluLoadSamplingMatrices</span></span></a> function.
                        This mode is initially set to <code class="constant">GLU_TRUE</code>.
                        Changing it from <code class="constant">GLU_TRUE</code> to <code class="constant">GLU_FALSE</code> does not affect
                        the sampling and culling matrices until 
                        <a class="citerefentry" href="gluLoadSamplingMatrices.xml"><span class="citerefentry"><span class="refentrytitle">gluLoadSamplingMatrices</span></span></a>
                        is called.
                    </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
            If <code class="constant">GLU_AUTO_LOAD_MATRIX</code> is true, sampling and culling may be
            executed incorrectly if NURBS routines are compiled into a display list.
        </p><p>
            A <em class="parameter"><code>property</code></em> of 
            <code class="constant">GLU_PARAMETRIC_TOLERANCE</code>,
            <code class="constant">GLU_SAMPLING_METHOD</code>,
            <code class="constant">GLU_U_STEP</code>, or
            <code class="constant">GLU_V_STEP</code>,
            or a <em class="parameter"><code>value</code></em> of 
            <code class="constant">GLU_PATH_LENGTH</code>,
            <code class="constant">GLU_PARAMETRIC_ERROR</code>, 
            <code class="constant">GLU_DOMAIN_DISTANCE</code> 
            are only available if the GLU version is 1.1 or greater. They are not
            valid parameters in GLU 1.0. 
        </p><p>
            <a class="citerefentry" href="gluGetString.xml"><span class="citerefentry"><span class="refentrytitle">gluGetString</span></span></a> can
            be used to determine the GLU version. 
        </p><p>
            <code class="constant">GLU_NURBS_MODE</code> is only available if the GLU version is 1.3 or
            greater.
        </p><p>
            The <code class="constant">GLU_OBJECT_PATH_LENGTH</code> and <code class="constant">GLU_OBJECT_PARAMETRIC_ERROR</code> 
            values for the <code class="constant">GLU_SAMPLING_METHOD</code> property are only available if 
            the GLU version is 1.3 or greater.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a class="citerefentry" href="gluGetNurbsProperty.xml"><span class="citerefentry"><span class="refentrytitle">gluGetNurbsProperty</span></span></a>,
            <a class="citerefentry" href="gluGetString.xml"><span class="citerefentry"><span class="refentrytitle">gluGetString</span></span></a>,
            <a class="citerefentry" href="gluLoadSamplingMatrices.xml"><span class="citerefentry"><span class="refentrytitle">gluLoadSamplingMatrices</span></span></a>,
            <a class="citerefentry" href="gluNewNurbsRenderer.xml"><span class="citerefentry"><span class="refentrytitle">gluNewNurbsRenderer</span></span></a>,
            <a class="citerefentry" href="gluNurbsCallback.xml"><span class="citerefentry"><span class="refentrytitle">gluNurbsCallback</span></span></a>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
            Copyright <span class="trademark"></span>© 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
        </p></div></div></body></html>
