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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="glClear">
<refmeta>
<refmetainfo>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
</refmetainfo>
<refentrytitle>glClear</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glClear</refname>
<refpurpose>clear buffers to preset values</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glClear</function></funcdef>
<paramdef>GLbitfield <parameter>mask</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>mask</parameter></term>
<listitem>
<para>
Bitwise OR of masks that indicate the buffers to be cleared.
The four masks are
<constant>GL_COLOR_BUFFER_BIT</constant>,
<constant>GL_DEPTH_BUFFER_BIT</constant>,
<constant>GL_ACCUM_BUFFER_BIT</constant>, and
<constant>GL_STENCIL_BUFFER_BIT</constant>.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
<function>glClear</function> sets the bitplane area of the window to values previously selected
by <function>glClearColor</function>, <function>glClearIndex</function>, <function>glClearDepth</function>,
<function>glClearStencil</function>, and <function>glClearAccum</function>.
Multiple color buffers can be cleared simultaneously by selecting
more than one buffer at a time using <citerefentry><refentrytitle>glDrawBuffer</refentrytitle></citerefentry>.
</para>
<para>
The pixel ownership test,
the scissor test,
dithering, and the buffer writemasks affect the operation of <function>glClear</function>.
The scissor box bounds the cleared region.
Alpha function,
blend function,
logical operation,
stenciling,
texture mapping,
and depth-buffering are ignored by <function>glClear</function>.
</para>
<para>
<function>glClear</function> takes a single argument that is the bitwise OR of several
values indicating which buffer is to be cleared.
</para>
<para>
The values are as follows:
</para>
<variablelist>
<varlistentry>
<term><constant>GL_COLOR_BUFFER_BIT</constant></term>
<listitem>
<para>
Indicates the buffers currently enabled for color
writing.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_DEPTH_BUFFER_BIT</constant></term>
<listitem>
<para>
Indicates the depth buffer.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_ACCUM_BUFFER_BIT</constant></term>
<listitem>
<para>
Indicates the accumulation buffer.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>GL_STENCIL_BUFFER_BIT</constant></term>
<listitem>
<para>
Indicates the stencil buffer.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
The value to which each buffer is cleared depends on the setting of the
clear value for that buffer.
</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para>
If a buffer is not present,
then a <function>glClear</function> directed at that buffer has no effect.
</para>
</refsect1>
<refsect1 id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_VALUE</constant> is generated if any bit other than the four defined
bits is set in <parameter>mask</parameter>.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated if <function>glClear</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_ACCUM_CLEAR_VALUE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_DEPTH_CLEAR_VALUE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_INDEX_CLEAR_VALUE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_COLOR_CLEAR_VALUE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_CLEAR_VALUE</constant>
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<function>glClearAccum</function>,
<function>glClearColor</function>,
<function>glClearDepth</function>,
<function>glClearIndex</function>,
<function>glClearStencil</function>,
<citerefentry><refentrytitle>glColorMask</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDepthMask</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDrawBuffer</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glScissor</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 1991-2006
Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see
<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
</para>
</refsect1>
</refentry>