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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<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 fragment color values or fragment data will
be written. If no fragment shader is active, rendering
operations will generate only one fragment color per fragment
and it will be written into each of the buffers specified by
<parameter>bufs</parameter>. If a fragment shader is active and
it writes a value to the output variable
<code>gl_FragColor</code>, then that value will be
written into each of the buffers specified by
<parameter>bufs</parameter>. If a fragment shader is active and
it writes a value to one or more elements of the output array
variable <code>gl_FragData[]</code>, then the value of
<code>gl_FragData[0] </code> will be written into the
first buffer specified by <parameter>bufs</parameter>, the value
of <code>gl_FragData[1] </code> will be written into the
second buffer specified by <parameter>bufs</parameter>, and so
on up to <code>gl_FragData[n-1]</code>. The draw buffer
used for <code>gl_FragData[n]</code> and beyond is
implicitly set to be <constant>GL_NONE</constant>.</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 color/data value is not written into
any color buffer.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_FRONT_LEFT</constant></term>
<listitem>
<para>The fragment color/data value is written into the
front left color buffer.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_FRONT_RIGHT</constant></term>
<listitem>
<para>The fragment color/data value is written into the
front right color buffer.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_BACK_LEFT</constant></term>
<listitem>
<para>The fragment color/data value is written into the
back left color buffer.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_BACK_RIGHT</constant></term>
<listitem>
<para>The fragment color/data value is written into the
back right color buffer.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_AUXi</constant></term>
<listitem>
<para>The fragment color/data value is written into
auxiliary buffer <code>i</code>.</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>. The
number of auxiliary buffers can be queried by calling
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
with the argument <constant>GL_AUX_BUFFERS</constant>.</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para><function>glDrawBuffers</function> is available only if
the GL version is 2.0 or greater.</para>
<para>It is always the case that <constant>GL_AUXi</constant> =
<constant>GL_AUX0</constant> + <code>i</code>.</para>
<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 writes to neither
<code>gl_FragColor</code> nor
<code>gl_FragData</code>, 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
<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>
<para><constant>GL_INVALID_OPERATION</constant> is generated if
<function>glDrawBuffers</function> is executed between the
execution of
<citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
and the corresponding execution of
<citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</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_BUFFERSi</constant> where
<code>i</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>glIndexMask</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>