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185 lines
8 KiB
XML
185 lines
8 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glDrawBuffers">
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<refmeta>
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<refentrytitle>glDrawBuffers</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glDrawBuffers</refname>
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<refpurpose>Specifies a list of color buffers to be drawn into</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glDrawBuffers</function></funcdef>
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<paramdef>GLsizei <parameter>n</parameter></paramdef>
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<paramdef>const GLenum *<parameter>bufs</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>n</parameter></term>
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<listitem>
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<para>Specifies the number of buffers in
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<parameter>bufs</parameter>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>bufs</parameter></term>
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<listitem>
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<para>Points to an array of symbolic constants
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specifying the buffers into which fragment colors or
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data values will be written.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para><function>glDrawBuffers</function> defines an array of
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buffers into which outputs from the fragment shader data will
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be written. If a fragment shader writes a value
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to one or more user defined output
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variables, then the value of each variable will be written into the
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buffer specified at a location within <parameter>bufs</parameter>
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corresponding to the location assigned to that user defined output.
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The draw buffer used for user defined outputs assigned to locations
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greater than or equal to <parameter>n</parameter> is implicitly set
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to <constant>GL_NONE</constant> and any data written to such an output
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is discarded.</para>
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<para>The symbolic constants contained in
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<parameter>bufs</parameter> may be any of the following:</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_NONE</constant></term>
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<listitem>
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<para>The fragment shader output value is not written into
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any color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_FRONT_LEFT</constant></term>
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<listitem>
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<para>The fragment shader output value is written into the
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front left color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_FRONT_RIGHT</constant></term>
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<listitem>
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<para>The fragment shader output value is written into the
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front right color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_BACK_LEFT</constant></term>
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<listitem>
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<para>The fragment shader output value is written into the
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back left color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_BACK_RIGHT</constant></term>
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<listitem>
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<para>The fragment shader output value is written into the
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back right color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_COLOR_ATTACHMENT<emphasis>n</emphasis></constant></term>
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<listitem>
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<para>The fragment shader output value is written into the
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<emphasis>n</emphasis>th color attachment of the current framebuffer.
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<emphasis>n</emphasis> may range from 0 to the value of
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<constant>GL_MAX_COLOR_ATTACHMENTS</constant>.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Except for <constant>GL_NONE</constant>, the preceding
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symbolic constants may not appear more than once in
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<parameter>bufs</parameter>. The maximum number of draw buffers
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supported is implementation dependent and can be queried by
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calling
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with the argument <constant>GL_MAX_DRAW_BUFFERS</constant>.</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>The symbolic constants <constant>GL_FRONT</constant>,
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<constant>GL_BACK</constant>, <constant>GL_LEFT</constant>,
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<constant>GL_RIGHT</constant>, and
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<constant>GL_FRONT_AND_BACK</constant> are not allowed in the
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<parameter>bufs</parameter> array since they may refer to
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multiple buffers.</para>
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<para>If a fragment shader does not write to a user defined output variable,
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the values of the fragment
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colors following shader execution are undefined. For each
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fragment generated in this situation, a different value may be
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written into each of the buffers specified by
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<parameter>bufs</parameter>.</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para><constant>GL_INVALID_ENUM</constant> is generated if one of the
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values in <parameter>bufs</parameter> is not an accepted
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value.</para>
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<para><constant>GL_INVALID_ENUM</constant> is generated if the GL is bound
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to the default framebuffer and one or more of the values in
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<parameter>bufs</parameter> is one of the <constant>GL_COLOR_ATTACHMENT<emphasis>n</emphasis></constant>
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tokens.</para>
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<para><constant>GL_INVALID_ENUM</constant> is generated if the GL is bound
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to a framebuffer object and one or more of the values in <parameter>bufs</parameter>
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is anything other than <constant>GL_NONE</constant> or one of the
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<constant>GL_COLOR_ATTACHMENT<emphasis>n</emphasis></constant> tokens.</para>
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<para><constant>GL_INVALID_ENUM</constant> is generated if
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<parameter>n</parameter> is less than 0.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if a
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symbolic constant other than <constant>GL_NONE</constant>
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appears more than once in <parameter>bufs</parameter>.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if any of
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the entries in <parameter>bufs</parameter> (other than
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<constant>GL_NONE</constant> ) indicates a color buffer that
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does not exist in the current GL context.</para>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>n</parameter> is greater than
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<constant>GL_MAX_DRAW_BUFFERS</constant>.</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with argument <constant>GL_MAX_DRAW_BUFFERS</constant></para>
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<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with argument <constant>GL_DRAW_BUFFER<emphasis>i</emphasis></constant> where
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<code><emphasis>i</emphasis></code> indicates the number of the draw buffer
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whose value is to be queried</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para> <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glColorMask</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawBuffers</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry></para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd.
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This material may be distributed subject to the terms and conditions set forth in
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the Open Publication License, v 1.0, 8 June 1999.
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<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
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</para>
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</refsect1>
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</refentry>
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