<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><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"><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><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"><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"><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"><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"><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"><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"><span class="citerefentry"><span class="refentrytitle">glEndQuery</span></span></a> is executed between the execution of

<a class="citerefentry" href="glBegin"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a> and the corresponding execution of

<a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

</p></div>

{$pipelinestall}{$examples}

<div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>

<a class="citerefentry" href="glDeleteQueries"><span class="citerefentry"><span class="refentrytitle">glDeleteQueries</span></span></a>,

<a class="citerefentry" href="glGenQueries"><span class="citerefentry"><span class="refentrytitle">glGenQueries</span></span></a>,

<a class="citerefentry" href="glGetQueryiv"><span class="citerefentry"><span class="refentrytitle">glGetQueryiv</span></span></a>,

<a class="citerefentry" href="glGetQueryObject"><span class="citerefentry"><span class="refentrytitle">glGetQueryObject</span></span></a>,

<a class="citerefentry" href="glIsQuery"><span class="citerefentry"><span class="refentrytitle">glIsQuery</span></span></a>

</p></div><div class="refsect1" lang="en" xml:lang="en"><div id="Copyright"><h2>Copyright</h2><p>

Copyright © 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="https://opencontent.org/openpub/" target="_top">https://opencontent.org/openpub/</a>.

</p></div></div></div>