<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>

<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glDebugMessageCallback">
    <info>
        <copyright>
            <year>2013-2014</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glDebugMessageCallback</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glDebugMessageCallback</refname>
        <refpurpose>specify a callback to receive debugging messages from the GL</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glDebugMessageCallback</function></funcdef>
                <paramdef>DEBUGPROC <parameter>callback</parameter></paramdef>
                <paramdef>const void * <parameter>userParam</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>callback</parameter></term>
            <listitem>
                <para>
                    The address of a callback function that will be called when a debug message is generated.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>userParam</parameter></term>
            <listitem>
                <para>
                    A user supplied pointer that will be passed on each invocation of <parameter>callback</parameter>.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            <function>glDebugMessageCallback</function> sets the current debug output callback function to
            the function whose address is given in <parameter>callback</parameter>. The callback function
            should have the following prototype (in C), or be otherwise compatible with such a prototype:
        </para>
<programlisting>        typedef void (APIENTRY *DEBUGPROC)(GLenum source,
            GLenum type,
            GLuint id,
            GLenum severity,
            GLsizei length,
            const GLchar *message,
            const void *userParam);</programlisting>
        <para>
            This function is defined to have the same calling convention as
            the GL API functions. In most cases this is defined as
            <code>APIENTRY</code>, although it will vary depending on
            platform, language and compiler.
        </para>
        <para>
            Each time a debug message is generated the debug callback
            function will be invoked with <parameter>source</parameter>,
            <parameter>type</parameter>, <parameter>id</parameter>, and
            <parameter>severity</parameter> associated with the message, and
            <parameter>length</parameter> set to the length of debug message
            whose character string is in the array pointed to by
            <parameter>message</parameter> <parameter>userParam</parameter>
            will be set to the value passed in the
            <parameter>userParam</parameter> parameter to the most recent
            call to <function>glDebugMessageCallback</function>.
        </para>
    </refsect1>
    <refsect1 xml:id="notes"><title>Notes</title>
        <para>
            When the GL is in use remotely, the server may not be able to
            call functions in the client's address space. In such cases, the
            callback function may not be invoked and the user should
            retrieve debug messages from the context's debug message log by
            calling
            <citerefentry><refentrytitle>glGetDebugMessageLog</refentrytitle></citerefentry>.
        </para>
    </refsect1>
    <refsect1 xml:id="versions"><title>Version Support</title>
        <informaltable>
            <tgroup cols="13" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry><function>glDebugMessageCallback</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='43']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glDebugMessageControl</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDebugMessageInsert</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGetDebugMessageLog</refentrytitle></citerefentry>.
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2013-2014 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>
