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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glDrawBuffers">
    <info>
        <copyright>
            <year>2003-2005</year>
            <holder>3Dlabs Inc. Ltd.</holder>
        </copyright>
        <copyright>
            <year>2010-2014</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glDrawBuffers</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glDrawBuffers</refname>
        <refpurpose>Specifies a list of color buffers to be drawn into</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
    <funcsynopsis>
        <funcprototype>
        <funcdef>void <function>glDrawBuffers</function></funcdef>
        <paramdef>GLsizei <parameter>n</parameter></paramdef>
        <paramdef>const GLenum *<parameter>bufs</parameter></paramdef>
        </funcprototype>
    </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
    <variablelist>
        <varlistentry>
        <term><parameter>n</parameter></term>
        <listitem>
            <para>Specifies the number of buffers in
            <parameter>bufs</parameter>.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>bufs</parameter></term>
        <listitem>
            <para>Points to an array of symbolic constants
            specifying the buffers into which fragment colors or
            data values will be written.</para>
        </listitem>
        </varlistentry>
    </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
    <para><function>glDrawBuffers</function> defines an array of
    buffers into which outputs from the fragment shader data will
    be written. If a fragment shader writes a value
    to one or more user defined output
    variables, then the value of each variable will be written into the
    buffer specified at a location within <parameter>bufs</parameter>
    corresponding to the location assigned to that user defined output.
    The draw buffer used for user defined outputs assigned to locations
    greater than or equal to <parameter>n</parameter> is implicitly set
    to <constant>GL_NONE</constant> and any data written to such an output
    is discarded.</para>

    <para>The symbolic constants contained in
    <parameter>bufs</parameter> must be one of the following, depending on
        whether GL is bound to the default framebuffer or not:</para>

    <variablelist>
        <varlistentry>
        <term><constant>GL_NONE</constant></term>
        <listitem>
            <para>The fragment shader output value is not written into
            any color buffer.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><constant>GL_BACK</constant></term>
        <listitem>
            <para>The fragment shader output value is written into the
            back color buffer.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><constant>GL_COLOR_ATTACHMENT</constant><emphasis>n</emphasis></term>
        <listitem>
            <para>The fragment shader output value is written into the
            <emphasis>n</emphasis>th color attachment of the current framebuffer.
            <emphasis>n</emphasis> may range from zero to the value of
            <constant>GL_MAX_COLOR_ATTACHMENTS</constant>.</para>
        </listitem>
        </varlistentry>
    </variablelist>

    <para>Except for <constant>GL_NONE</constant>, the preceding
    symbolic constants may not appear more than once in
    <parameter>bufs</parameter>. The maximum number of draw buffers
    supported is implementation dependent and can be queried by
    calling
    <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
    with the argument <constant>GL_MAX_DRAW_BUFFERS</constant>.</para>
    </refsect1>
    <refsect1 xml:id="notes"><title>Notes</title>

    <para>If a fragment shader does not write to a user defined output variable,
    the values of the fragment
    colors following shader execution are undefined. For each
    fragment generated in this situation, a different value may be
    written into each of the buffers specified by
    <parameter>bufs</parameter>.</para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
    <para><constant>GL_INVALID_ENUM</constant> is generated if one of the
    values in <parameter>bufs</parameter> is not an accepted
    value.</para>
    
    <para><constant>GL_INVALID_OPERATION</constant> is generated if the GL is bound
    to the default framebuffer and <parameter>n</parameter> is not 1, or if the value in
    <parameter>bufs</parameter> is one of the <constant>GL_COLOR_ATTACHMENT</constant><emphasis>n</emphasis>
    tokens.</para>

    <para><constant>GL_INVALID_OPERATION</constant> is generated if the GL is bound
    to a framebuffer object and the ith buffer listed in <parameter>bufs</parameter>
    is anything other than <constant>GL_NONE</constant> or 
    <constant>GL_COLOR_ATTACHMENTS</constant><emphasis>i</emphasis>.</para>

    <para><constant>GL_INVALID_VALUE</constant> is generated if
    <parameter>n</parameter> is less than 0 or greater than
    <constant>GL_MAX_DRAW_BUFFERS</constant>.</para>

    </refsect1>
    <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
    <para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
    with argument <constant>GL_MAX_DRAW_BUFFERS</constant></para>

    <para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
    with argument <constant>GL_DRAW_BUFFER</constant><emphasis>i</emphasis> where
    <emphasis>i</emphasis> indicates the number of the draw buffer
    whose value is to be queried.</para>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="3" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry>glDrawBuffers</entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es30']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2003-2005 3Dlabs Inc. Ltd.
            Copyright <trademark class="copyright"/> 2010-2014 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>
