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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>glBeginQuery</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glBeginQuery"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glBeginQuery — delimit the boundaries of a query object</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">glBeginQuery</b>(</code></td><td>GLenum  </td><td><var class="pdparam">target</var>, </td></tr><tr><td> </td><td>GLuint  </td><td><var class="pdparam">id</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>target</code></em></span></dt><dd><p>
                    Specifies the target type of query object established between
                    <code class="function">glBeginQuery</code> and the subsequent <a class="citerefentry" href="glEndQuery.xml"><span class="citerefentry"><span class="refentrytitle">glEndQuery</span></span></a>.
                    The symbolic constant must be <code class="constant">GL_SAMPLES_PASSED</code>.
                </p></dd><dt><span class="term"><em class="parameter"><code>id</code></em></span></dt><dd><p>
                    Specifies the name of a query object.
                </p></dd></dl></div></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">glEndQuery</b>(</code></td><td>GLenum  </td><td><var class="pdparam">target</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters2"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>target</code></em></span></dt><dd><p>
                    Specifies the target type of query object to be concluded.
                    The symbolic constant must be <code class="constant">GL_SAMPLES_PASSED</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">glBeginQuery</code> and <a class="citerefentry" href="glEndQuery.xml"><span class="citerefentry"><span class="refentrytitle">glEndQuery</span></span></a> delimit the
            boundaries of a query object.  If a query object with name <em class="parameter"><code>id</code></em> does not yet exist it is created.
        </p><p>
            When <code class="function">glBeginQuery</code> is executed, the query object's samples-passed counter is reset to 0.  Subsequent
            rendering will increment the counter once for every sample that passes the depth test.  When <code class="function">glEndQuery</code>
            is executed, the samples-passed counter is assigned to the query object's result value.  This value can be queried by
            calling <a class="citerefentry" href="glGetQueryObject.xml"><span class="citerefentry"><span class="refentrytitle">glGetQueryObject</span></span></a> with <em class="parameter"><code>pname</code></em>
            <code class="constant">GL_QUERY_RESULT</code>.
        </p><p>
            Querying the <code class="constant">GL_QUERY_RESULT</code> implicitly flushes the GL pipeline until the rendering delimited by the
            query object has completed and the result is available.  <code class="constant">GL_QUERY_RESULT_AVAILABLE</code> can be queried to
            determine if the result is immediately available or if the rendering is not yet complete.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
            If the samples-passed count exceeds the maximum value representable in the number of available bits, as reported by
            <a class="citerefentry" href="glGetQueryiv.xml"><span class="citerefentry"><span class="refentrytitle">glGetQueryiv</span></span></a> with <em class="parameter"><code>pname</code></em>
            <code class="constant">GL_QUERY_COUNTER_BITS</code>, the count becomes undefined.
        </p><p>
            An implementation may support 0 bits in its samples-passed counter, in which case query results are always undefined
            and essentially useless.
        </p><p>
            When <code class="constant">GL_SAMPLE_BUFFERS</code> is 0, the samples-passed counter will increment once for each fragment that passes
            the depth test.  When <code class="constant">GL_SAMPLE_BUFFERS</code> is 1, an implementation may either increment the samples-passed
            counter individually for each sample of a fragment that passes the depth test, or it may choose to increment the counter for
            all samples of a fragment if any one of them passes the depth test.
        </p><p>
            <code class="function">glBeginQuery</code> and <a class="citerefentry" href="glEndQuery.xml"><span class="citerefentry"><span class="refentrytitle">glEndQuery</span></span></a>
            are available only if the GL version is 1.5 or greater.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>
            <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>target</code></em> is not <code class="constant">GL_SAMPLES_PASSED</code>.
        </p><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glBeginQuery</code> is executed while
            a query object of the same <em class="parameter"><code>target</code></em> is already active.
        </p><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <a class="citerefentry" href="glEndQuery.xml"><span class="citerefentry"><span class="refentrytitle">glEndQuery</span></span></a>
            is executed when a query object of the same <em class="parameter"><code>target</code></em> is not active.
        </p><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>id</code></em> is 0.
        </p><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>id</code></em> is the name of an already active query object.
        </p><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glBeginQuery</code> or
            <a class="citerefentry" href="glEndQuery.xml"><span class="citerefentry"><span class="refentrytitle">glEndQuery</span></span></a> is executed between the execution of
            <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a> and the corresponding execution of
            <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a class="citerefentry" href="glDeleteQueries.xml"><span class="citerefentry"><span class="refentrytitle">glDeleteQueries</span></span></a>,
            <a class="citerefentry" href="glGenQueries.xml"><span class="citerefentry"><span class="refentrytitle">glGenQueries</span></span></a>,
            <a class="citerefentry" href="glGetQueryiv.xml"><span class="citerefentry"><span class="refentrytitle">glGetQueryiv</span></span></a>,
            <a class="citerefentry" href="glGetQueryObject.xml"><span class="citerefentry"><span class="refentrytitle">glGetQueryObject</span></span></a>,
            <a class="citerefentry" href="glIsQuery.xml"><span class="citerefentry"><span class="refentrytitle">glIsQuery</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>© 2005 Addison-Wesley. 
            This material may be distributed subject to the terms and conditions set forth in 
            the Open Publication License, v 1.0, 8 June 1999.
            <a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
        </p></div></div></body></html>
