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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
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<!-- Converted by db4-upgrade version 1.1 -->
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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glStencilOpSeparate">
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<info>
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2013-11-03 11:43:50 +00:00
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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2014-03-28 19:06:55 +00:00
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<copyright>
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<year>2010-2014</year>
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<holder>Khronos Group</holder>
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</copyright>
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</info>
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2009-03-08 00:46:58 +00:00
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<refmeta>
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<refentrytitle>glStencilOpSeparate</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glStencilOpSeparate</refname>
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<refpurpose>set front and/or back stencil test actions</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<title>C Specification</title>
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2009-03-08 00:46:58 +00:00
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glStencilOpSeparate</function></funcdef>
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<paramdef>GLenum <parameter>face</parameter></paramdef>
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<paramdef>GLenum <parameter>sfail</parameter></paramdef>
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<paramdef>GLenum <parameter>dpfail</parameter></paramdef>
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<paramdef>GLenum <parameter>dppass</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 xml:id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>face</parameter></term>
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<listitem>
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<para>
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Specifies whether front and/or back stencil state is updated.
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Three symbolic constants are valid:
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<constant>GL_FRONT</constant>,
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<constant>GL_BACK</constant>, and
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<constant>GL_FRONT_AND_BACK</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>sfail</parameter></term>
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<listitem>
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<para>
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Specifies the action to take when the stencil test fails.
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Eight symbolic constants are accepted:
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<constant>GL_KEEP</constant>,
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<constant>GL_ZERO</constant>,
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<constant>GL_REPLACE</constant>,
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<constant>GL_INCR</constant>,
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<constant>GL_INCR_WRAP</constant>,
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<constant>GL_DECR</constant>,
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<constant>GL_DECR_WRAP</constant>, and
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<constant>GL_INVERT</constant>. The initial value is <constant>GL_KEEP</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>dpfail</parameter></term>
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<listitem>
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<para>
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Specifies the stencil action when the stencil test passes,
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but the depth test fails.
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<parameter>dpfail</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
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is <constant>GL_KEEP</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>dppass</parameter></term>
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<listitem>
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<para>
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Specifies the stencil action when both the stencil test and the depth
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test pass, or when the stencil test passes and either there is no
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depth buffer or depth testing is not enabled.
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<parameter>dppass</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
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is <constant>GL_KEEP</constant>.
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</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 xml:id="description"><title>Description</title>
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<para>
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Stenciling,
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like depth-buffering,
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enables and disables drawing on a per-pixel basis.
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You draw into the stencil planes using GL drawing primitives,
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then render geometry and images,
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using the stencil planes to mask out portions of the screen.
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Stenciling is typically used in multipass rendering algorithms
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to achieve special effects,
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such as decals,
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outlining,
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and constructive solid geometry rendering.
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</para>
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<para>
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The stencil test conditionally eliminates a pixel based on the outcome
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of a comparison between the value in the stencil buffer and a
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reference value. To enable and disable the test, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>
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and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument
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<constant>GL_STENCIL_TEST</constant>; to control it, call
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<citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> or
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<citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>.
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</para>
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<para>
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There can be two separate sets of <parameter>sfail</parameter>, <parameter>dpfail</parameter>, and
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<parameter>dppass</parameter> parameters; one affects back-facing polygons, and the other
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affects front-facing polygons as well as other non-polygon primitives.
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<citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> sets both front
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and back stencil state to the same values, as if
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<function>glStencilOpSeparate</function> were called
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with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>.
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</para>
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<para>
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<function>glStencilOpSeparate</function> takes three arguments that indicate what happens
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to the stored stencil value while stenciling is enabled.
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If the stencil test fails,
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no change is made to the pixel's color or depth buffers,
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and <parameter>sfail</parameter> specifies what happens to the stencil buffer contents.
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The following eight actions are possible.
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</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_KEEP</constant></term>
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<listitem>
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<para>
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Keeps the current value.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_ZERO</constant></term>
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<listitem>
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<para>
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Sets the stencil buffer value to 0.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_REPLACE</constant></term>
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<listitem>
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<para>
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Sets the stencil buffer value to <emphasis>ref</emphasis>,
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as specified by <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_INCR</constant></term>
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<listitem>
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<para>
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Increments the current stencil buffer value.
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Clamps to the maximum representable unsigned value.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_INCR_WRAP</constant></term>
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<listitem>
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<para>
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Increments the current stencil buffer value.
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Wraps stencil buffer value to zero when incrementing the maximum
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representable unsigned value.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_DECR</constant></term>
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<listitem>
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<para>
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Decrements the current stencil buffer value.
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Clamps to 0.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_DECR_WRAP</constant></term>
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<listitem>
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<para>
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Decrements the current stencil buffer value.
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Wraps stencil buffer value to the maximum representable unsigned value when
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decrementing a stencil buffer value of zero.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_INVERT</constant></term>
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<listitem>
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<para>
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Bitwise inverts the current stencil buffer value.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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Stencil buffer values are treated as unsigned integers.
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When incremented and decremented,
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values are clamped to 0 and
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<inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
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<!-- eqn: 2 sup n - 1:-->
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<mml:mrow>
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<mml:msup><mml:mn>2</mml:mn>
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<mml:mi mathvariant="italic">n</mml:mi>
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</mml:msup>
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<mml:mo>-</mml:mo>
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<mml:mn>1</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>,
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where
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<inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
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is the value returned by querying <constant>GL_STENCIL_BITS</constant>.
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</para>
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<para>
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The other two arguments to <function>glStencilOpSeparate</function> specify stencil buffer actions
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that depend on whether subsequent depth buffer tests succeed (<parameter>dppass</parameter>)
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or fail (<parameter>dpfail</parameter>) (see
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<citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>).
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The actions are specified using the same eight symbolic constants as <parameter>sfail</parameter>.
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Note that <parameter>dpfail</parameter> is ignored when there is no depth buffer,
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or when the depth buffer is not enabled.
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In these cases, <parameter>sfail</parameter> and <parameter>dppass</parameter> specify stencil action when the
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stencil test fails and passes,
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respectively.
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</para>
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</refsect1>
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<refsect1 xml:id="notes"><title>Notes</title>
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<para>
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Initially the stencil test is disabled.
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If there is no stencil buffer,
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no stencil modification can occur
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and it is as if the stencil test always passes.
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</para>
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</refsect1>
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<refsect1 xml:id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>face</parameter> is any value
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other than <constant>GL_FRONT</constant>, <constant>GL_BACK</constant>, or <constant>GL_FRONT_AND_BACK</constant>.
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</para>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>sfail</parameter>,
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<parameter>dpfail</parameter>, or <parameter>dppass</parameter> is any value other than the eight defined constant values.
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</para>
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</refsect1>
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<refsect1 xml:id="associatedgets"><title>Associated Gets</title>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument
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<constant>GL_STENCIL_FAIL</constant>, <constant>GL_STENCIL_PASS_DEPTH_PASS</constant>,
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<constant>GL_STENCIL_PASS_DEPTH_FAIL</constant>, <constant>GL_STENCIL_BACK_FAIL</constant>,
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<constant>GL_STENCIL_BACK_PASS_DEPTH_PASS</constant>, <constant>GL_STENCIL_BACK_PASS_DEPTH_FAIL</constant>,
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or <constant>GL_STENCIL_BITS</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_TEST</constant>
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</para>
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</refsect1>
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<refsect1 xml:id="versions">
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<title>API Version Support</title>
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<informaltable>
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<tgroup cols="4" align="left">
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
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<tbody>
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<row>
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<entry>glStencilOpSeparate</entry>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</refsect1>
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<refsect1 xml:id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>
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</para>
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</refsect1>
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2014-03-28 19:06:55 +00:00
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<refsect1 xml:id="Copyright"><title>Copyright</title>
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2009-03-08 00:46:58 +00:00
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<para>
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2014-03-28 19:06:55 +00:00
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Copyright <trademark class="copyright"/> 1991-2006 Silicon Graphics, Inc.
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Copyright <trademark class="copyright"/> 2010-2014 Khronos Group.
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This document is licensed under the SGI Free Software B License.
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For details, see
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<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</link>.
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2009-03-08 00:46:58 +00:00
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</para>
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</refsect1>
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</refentry>
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