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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="4" 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']/*)"/>
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</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>