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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glBeginQuery">
    <info>
        <copyright>
            <year>2005</year>
            <holder>Sams Publishing</holder>
        </copyright>
        <copyright>
            <year>2010-2013</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glBeginQuery</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glBeginQuery</refname>
        <refpurpose>delimit the boundaries of a query object</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glBeginQuery</function></funcdef>
                <paramdef>GLenum <parameter>target</parameter></paramdef>
                <paramdef>GLuint <parameter>id</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glEndQuery</function></funcdef>
                <paramdef>GLenum <parameter>target</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters for <function>glBeginQuery</function></title>
        <variablelist>
        <varlistentry>
            <term><parameter>target</parameter></term>
            <listitem>
                <para>
                    Specifies the target type of query object established between
                    <function>glBeginQuery</function> and the subsequent <citerefentry><refentrytitle>glEndQuery</refentrytitle></citerefentry>.
                    The symbolic constant must be one of <constant>GL_SAMPLES_PASSED</constant>, <constant>GL_ANY_SAMPLES_PASSED</constant>,
                    <constant>GL_ANY_SAMPLES_PASSED_CONSERVATIVE</constant>,
                    <constant>GL_PRIMITIVES_GENERATED</constant>, <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, or
                    <constant>GL_TIME_ELAPSED</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>id</parameter></term>
            <listitem>
                <para>
                    Specifies the name of a query object.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="parameters2"><title>Parameters for <function>glEndQuery</function></title>
        <variablelist>
        <varlistentry>
            <term><parameter>target</parameter></term>
            <listitem>
                <para>
                    Specifies the target type of query object to be concluded.
                    The symbolic constant must be one of <constant>GL_SAMPLES_PASSED</constant>, <constant>GL_ANY_SAMPLES_PASSED</constant>,
                    <constant>GL_ANY_SAMPLES_PASSED_CONSERVATIVE</constant>,
                    <constant>GL_PRIMITIVES_GENERATED</constant>, <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, or
                    <constant>GL_TIME_ELAPSED</constant>.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            <function>glBeginQuery</function> and <citerefentry><refentrytitle>glEndQuery</refentrytitle></citerefentry> delimit the
            boundaries of a query object.  <parameter>query</parameter> must be a name previously returned from a call to
            <citerefentry><refentrytitle>glGenQueries</refentrytitle></citerefentry>. If a query object with name <parameter>id</parameter>
            does not yet exist it is created with the type determined by <parameter>target</parameter>. <parameter>target</parameter> must
            be one of <constant>GL_SAMPLES_PASSED</constant>, <constant>GL_ANY_SAMPLES_PASSED</constant>, <constant>GL_PRIMITIVES_GENERATED</constant>,
            <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, or <constant>GL_TIME_ELAPSED</constant>. The behavior of the query
            object depends on its type and is as follows.
        </para>
        <para>
            If <parameter>target</parameter> is <constant>GL_SAMPLES_PASSED</constant>, <parameter>id</parameter> must be an unused name,
            or the name of an existing occlusion query object.
            When <function>glBeginQuery</function> is executed, the query object's samples-passed counter is reset to 0.  Subsequent
            rendering will increment the counter for every sample that passes the depth test.  If the value of <constant>GL_SAMPLE_BUFFERS</constant>
            is 0, then the samples-passed count is incremented by 1 for each fragment. If the value of <constant>GL_SAMPLE_BUFFERS</constant>
            is 1, then the samples-passed count is incremented by the number of samples whose coverage bit is set. However, implementations, at their
            discression may instead increase the samples-passed count by the value of <constant>GL_SAMPLES</constant> if any sample in the fragment
            is covered. When <function>glEndQuery</function>
            is executed, the samples-passed counter is assigned to the query object's result value.  This value can be queried by
            calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
            <constant>GL_QUERY_RESULT</constant>.
        </para>
        <para>
            If <parameter>target</parameter> is <constant>GL_ANY_SAMPLES_PASSED</constant> or <constant>GL_ANY_SAMPLES_PASSED_CONSERVATIVE</constant>,
            <parameter>id</parameter> must be an unused name, or the name of an existing boolean occlusion query object.
            When <function>glBeginQuery</function> is executed, the query object's samples-passed flag is reset to <constant>GL_FALSE</constant>.
            Subsequent rendering causes the flag to be set to <constant>GL_TRUE</constant> if any sample passes the depth test in the case of <constant>GL_ANY_SAMPLES_PASSED</constant>,
            or if the implementation determines that any sample might pass the depth test in the case of <constant>GL_ANY_SAMPLES_PASSED_CONSERVATIVE</constant>.
            The implementation may be able to provide a more efficient test in the case of <constant>GL_ANY_SAMPLES_PASSED_CONSERVATIVE</constant>
            if some false positives are acceptable to the application.  When
            <function>glEndQuery</function> is executed, the samples-passed flag is assigned to the query object's result value.  This value can
            be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
            <constant>GL_QUERY_RESULT</constant>.
        </para>
        <para>
            If <parameter>target</parameter> is <constant>GL_PRIMITIVES_GENERATED</constant>, <parameter>id</parameter> must be an unused
            name, or the name of an existing primitive query object previously bound to the <constant>GL_PRIMITIVES_GENERATED</constant> query binding.
            When <function>glBeginQuery</function> is executed, the query object's primitives-generated counter is reset to 0.  Subsequent
            rendering will increment the counter once for every vertex that is emitted from the geometry shader, or from the vertex shader if
            no geometry shader is present.  When <function>glEndQuery</function> is executed, the primitives-generated counter is assigned to
            the query object's result value.  This value can be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
            <constant>GL_QUERY_RESULT</constant>.
        </para>
        <para>
            If <parameter>target</parameter> is <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>, <parameter>id</parameter> must be
            an unused name, or the name of an existing primitive query object previously bound to the <constant>GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN</constant>
            query binding. When <function>glBeginQuery</function> is executed, the query object's primitives-written counter is reset to 0.  Subsequent
            rendering will increment the counter once for every vertex that is written into the bound transform feedback buffer(s).  If transform feedback
            mode is not activated between the call to <function>glBeginQuery</function> and <function>glEndQuery</function>, the counter will not be
            incremented.  When <function>glEndQuery</function> is executed, the primitives-written counter is assigned to
            the query object's result value.  This value can be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
            <constant>GL_QUERY_RESULT</constant>.
        </para>
        <para>
            If <parameter>target</parameter> is <constant>GL_TIME_ELAPSED</constant>, <parameter>id</parameter> must be
            an unused name, or the name of an existing timer query object previously bound to the <constant>GL_TIME_ELAPSED</constant>
            query binding. When <function>glBeginQuery</function> is executed, the query object's time counter is reset to 0.  When <function>glEndQuery</function>
            is executed, the elapsed server time that has passed since the call to <function>glBeginQuery</function> is written into the query object's
            time counter.  This value can be queried by calling <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry> with <parameter>pname</parameter>
            <constant>GL_QUERY_RESULT</constant>.
        </para>
        <para>
            Querying the <constant>GL_QUERY_RESULT</constant> implicitly flushes the GL pipeline until the rendering delimited by the
            query object has completed and the result is available.  <constant>GL_QUERY_RESULT_AVAILABLE</constant> can be queried to
            determine if the result is immediately available or if the rendering is not yet complete.
        </para>
    </refsect1>
    <refsect1 xml:id="notes"><title>Notes</title>
        <para>
            If the query target's count exceeds the maximum value representable in the number of available bits, as reported by
            <citerefentry><refentrytitle>glGetQueryiv</refentrytitle></citerefentry> with <parameter>target</parameter> set to the
            appropriate query target and <parameter>pname</parameter>
            <constant>GL_QUERY_COUNTER_BITS</constant>, the count becomes undefined.
        </para>
        <para>
            An implementation may support 0 bits in its counter, in which case query results are always undefined
            and essentially useless.
        </para>
        <para>
            When <constant>GL_SAMPLE_BUFFERS</constant> is 0, the samples-passed counter of an occlusion query will increment once for each
            fragment that passes the depth test.  When <constant>GL_SAMPLE_BUFFERS</constant> 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.
        </para>
        <para>
            The query targets <constant>GL_ANY_SAMPLES_PASSED</constant>, and <constant>GL_TIME_ELAPSED</constant> are availale only if
            the GL version is 3.3 or higher.
        </para>
        <para>
            The query target <constant>GL_ANY_SAMPLES_PASSED_CONSERVATIVE</constant> is available only of the GL version is 4.3 or higher.
        </para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter> is not one of the accepted tokens.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glBeginQuery</function> is executed while
            a query object of the same <parameter>target</parameter> is already active.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <citerefentry><refentrytitle>glEndQuery</refentrytitle></citerefentry>
            is executed when a query object of the same <parameter>target</parameter> is not active.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>id</parameter> is 0.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>id</parameter> is the name of an already active query object.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>id</parameter> refers to an existing query object whose type
            does not does not match <parameter>target</parameter>.
        </para>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glDeleteQueries</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGenQueries</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGetQueryiv</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGetQueryObject</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glIsQuery</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2005 Addison-Wesley.
            Copyright <trademark class="copyright"/> 2010-2013 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.
            <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
        </para>
    </refsect1>
</refentry>
