<div class="refentry"><a id="glBeginConditionalRender"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glBeginConditionalRender — start conditional rendering</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <strong class="fsfunc">glBeginConditionalRender</strong>(</code></td><td>GLuint <var class="pdparam">id</var>, </td></tr><tr><td> </td><td>GLenum <var class="pdparam">mode</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>id</code></em></span></dt><dd><p>

Specifies the name of an occlusion query object whose results are used to determine if the rendering commands are discarded.

</p></dd><dt><span class="term"><em class="parameter"><code>mode</code></em></span></dt><dd><p>

Specifies how <code class="function">glBeginConditionalRender</code> interprets the results of the occlusion query.

</p></dd></dl></div></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <strong class="fsfunc">glEndConditionalRender</strong>(</code></td><td><var class="pdparam">void</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a id="description"></a><h2>Description</h2><p>

Conditional rendering is started using <code class="function">glBeginConditionalRender</code> and ended using <code class="function">glEndConditionalRender</code>.

During conditional rendering, all vertex array commands, as well as <a class="citerefentry" href="glClear"><span class="citerefentry"><span class="refentrytitle">glClear</span></span></a> and

<a class="citerefentry" href="glClearBuffer"><span class="citerefentry"><span class="refentrytitle">glClearBuffer</span></span></a> have no effect if the (<code class="constant">GL_SAMPLES_PASSED</code>) result

of the query object <em class="parameter"><code>id</code></em> is zero, or if the (<code class="constant">GL_ANY_SAMPLES_PASSED</code>) result is <code class="constant">GL_FALSE</code>.

The results of commands setting the current vertex state, such as <a class="citerefentry" href="glVertexAttrib"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a> are

undefined. If the (<code class="constant">GL_SAMPLES_PASSED</code>) result is non-zero or if the (<code class="constant">GL_ANY_SAMPLES_PASSED</code>) result is

<code class="constant">GL_TRUE</code>, such commands are not discarded. The <em class="parameter"><code>id</code></em> parameter to <code class="function">glBeginConditionalRender</code>

must be the name of a query object previously returned from a call to <a class="citerefentry" href="glGenQueries"><span class="citerefentry"><span class="refentrytitle">glGenQueries</span></span></a>.

<em class="parameter"><code>mode</code></em> specifies how the results of the query object are to be interpreted. If <em class="parameter"><code>mode</code></em> is

<code class="constant">GL_QUERY_WAIT</code>, the GL waits for the results of the query to be available and then uses the results to determine if subsequent

rendering commands are discarded. If <em class="parameter"><code>mode</code></em> is <code class="constant">GL_QUERY_NO_WAIT</code>, the GL may choose to unconditionally

execute the subsequent rendering commands without waiting for the query to complete.

</p><p>

If <em class="parameter"><code>mode</code></em> is <code class="constant">GL_QUERY_BY_REGION_WAIT</code>, the GL will also wait for occlusion query results and discard

rendering commands if the result of the occlusion query is zero. If the query result is non-zero, subsequent rendering commands are executed,

but the GL may discard the results of the commands for any region of the framebuffer that did not contribute to the sample count in the specified

occlusion query. Any such discarding is done in an implementation-dependent manner, but the rendering command results may not be discarded for

any samples that contributed to the occlusion query sample count. If <em class="parameter"><code>mode</code></em> is <code class="constant">GL_QUERY_BY_REGION_NO_WAIT</code>,

the GL operates as in <code class="constant">GL_QUERY_BY_REGION_WAIT</code>, but may choose to unconditionally execute the subsequent rendering commands

without waiting for the query to complete.

</p></div><div class="refsect1"><a id="notes"></a><h2>Notes</h2><p>

<code class="function">glBeginConditionalRender</code> and <code class="function">glEndConditionalRender</code> are available only if the GL version is 3.0 or greater.

</p><p>

The <code class="constant">GL_ANY_SAMPLES_PASSED</code> query result is available only if the GL version is 3.3 or greater.

</p></div><div class="refsect1"><a id="errors"></a><h2>Errors</h2><p>

<code class="constant">GL_INVALID_VALUE</code> is generated if <em class="parameter"><code>id</code></em> is not the name of an existing query object.

</p><p>

<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>mode</code></em> is not one of the accepted tokens.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glBeginConditionalRender</code> is called while conditional rendering is active,

or if <code class="function">glEndConditionalRender</code> is called while conditional rendering is inactive.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>id</code></em> is the name of a query object with a target other than

<code class="constant">GL_SAMPLES_PASSED</code> or <code class="constant">GL_ANY_SAMPLES_PASSED</code>.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>id</code></em> is the name of a query currently in progress.

</p></div>

{$pipelinestall}{$examples}

<div class="refsect1"><a id="seealso"></a><h2>See Also</h2><p>

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

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

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

</p></div><div class="refsect1"><div id="Copyright"><h2>Copyright</h2><p>

Copyright © 2009 Khronos Group.

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>