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<refentry id="glDrawBuffers">
    <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 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 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> may be any of the following:</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_FRONT_LEFT</constant></term>
        <listitem>
            <para>The fragment shader output value is written into the
            front left color buffer.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><constant>GL_FRONT_RIGHT</constant></term>
        <listitem>
            <para>The fragment shader output value is written into the
            front right color buffer.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><constant>GL_BACK_LEFT</constant></term>
        <listitem>
            <para>The fragment shader output value is written into the
            back left color buffer.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><constant>GL_BACK_RIGHT</constant></term>
        <listitem>
            <para>The fragment shader output value is written into the
            back right color buffer.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><constant>GL_COLOR_ATTACHMENT<emphasis>n</emphasis></constant></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 0 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 id="notes"><title>Notes</title>

    <para>The symbolic constants <constant>GL_FRONT</constant>,
    <constant>GL_BACK</constant>, <constant>GL_LEFT</constant>,
    <constant>GL_RIGHT</constant>, and
    <constant>GL_FRONT_AND_BACK</constant> are not allowed in the
    <parameter>bufs</parameter> array since they may refer to
    multiple buffers.</para>

    <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 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_ENUM</constant> is generated if the GL is bound
    to the default framebuffer and one or more of the values in
    <parameter>bufs</parameter> is one of the <constant>GL_COLOR_ATTACHMENT<emphasis>n</emphasis></constant>
    tokens.</para>

    <para><constant>GL_INVALID_ENUM</constant> is generated if the GL is bound
    to a framebuffer object and one or more of the values in <parameter>bufs</parameter>
    is anything other than <constant>GL_NONE</constant> or one of the
    <constant>GL_COLOR_ATTACHMENT<emphasis>n</emphasis></constant> tokens.</para>

    <para><constant>GL_INVALID_ENUM</constant> is generated if
    <parameter>n</parameter> is less than 0.</para>

    <para><constant>GL_INVALID_OPERATION</constant> is generated if a
    symbolic constant other than <constant>GL_NONE</constant>
    appears more than once in <parameter>bufs</parameter>.</para>

    <para><constant>GL_INVALID_OPERATION</constant> is generated if any of
    the entries in <parameter>bufs</parameter> (other than
    <constant>GL_NONE</constant> ) indicates a color buffer that
    does not exist in the current GL context.</para>

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

    </refsect1>
    <refsect1 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<emphasis>i</emphasis></constant> where
    <code><emphasis>i</emphasis></code> indicates the number of the draw buffer
    whose value is to be queried</para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
    <para> <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glColorMask</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glDrawBuffers</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd. 
            This material may be distributed subject to the terms and conditions set forth in 
            the Open Publication License, v 1.0, 8 June 1999.
            <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
        </para>
    </refsect1>
</refentry>
