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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="glStencilOpSeparate">
+ <refmeta>
+ <refmetainfo>
+ <copyright>
+ <year>1991-2006</year>
+ <holder>Silicon Graphics, Inc.</holder>
+ </copyright>
+ </refmetainfo>
+ <refentrytitle>glStencilOpSeparate</refentrytitle>
+ <manvolnum>3G</manvolnum>
+ </refmeta>
+ <refnamediv>
+ <refname>glStencilOpSeparate</refname>
+ <refpurpose>set front and/or back stencil test actions</refpurpose>
+ </refnamediv>
+ <!-- eqn: ignoring delim $$ -->
+ <refsynopsisdiv><title>C Specification</title>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>void <function>glStencilOpSeparate</function></funcdef>
+ <paramdef>GLenum <parameter>face</parameter></paramdef>
+ <paramdef>GLenum <parameter>sfail</parameter></paramdef>
+ <paramdef>GLenum <parameter>dpfail</parameter></paramdef>
+ <paramdef>GLenum <parameter>dppass</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+ <refsect1 id="parameters"><title>Parameters</title>
+ <variablelist>
+ <varlistentry>
+ <term><parameter>face</parameter></term>
+ <listitem>
+ <para>
+ Specifies whether front and/or back stencil state is updated.
+ Three symbolic constants are valid:
+ <constant>GL_FRONT</constant>,
+ <constant>GL_BACK</constant>, and
+ <constant>GL_FRONT_AND_BACK</constant>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>sfail</parameter></term>
+ <listitem>
+ <para>
+ Specifies the action to take when the stencil test fails.
+ Eight symbolic constants are accepted:
+ <constant>GL_KEEP</constant>,
+ <constant>GL_ZERO</constant>,
+ <constant>GL_REPLACE</constant>,
+ <constant>GL_INCR</constant>,
+ <constant>GL_INCR_WRAP</constant>,
+ <constant>GL_DECR</constant>,
+ <constant>GL_DECR_WRAP</constant>, and
+ <constant>GL_INVERT</constant>. The initial value is <constant>GL_KEEP</constant>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>dpfail</parameter></term>
+ <listitem>
+ <para>
+ Specifies the stencil action when the stencil test passes,
+ but the depth test fails.
+ <parameter>dpfail</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
+ is <constant>GL_KEEP</constant>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>dppass</parameter></term>
+ <listitem>
+ <para>
+ Specifies the stencil action when both the stencil test and the depth
+ test pass, or when the stencil test passes and either there is no
+ depth buffer or depth testing is not enabled.
+ <parameter>dppass</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
+ is <constant>GL_KEEP</constant>.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+ <refsect1 id="description"><title>Description</title>
+ <para>
+ Stenciling,
+ like depth-buffering,
+ enables and disables drawing on a per-pixel basis.
+ You draw into the stencil planes using GL drawing primitives,
+ then render geometry and images,
+ using the stencil planes to mask out portions of the screen.
+ Stenciling is typically used in multipass rendering algorithms
+ to achieve special effects,
+ such as decals,
+ outlining,
+ and constructive solid geometry rendering.
+ </para>
+ <para>
+ The stencil test conditionally eliminates a pixel based on the outcome
+ of a comparison between the value in the stencil buffer and a
+ reference value. To enable and disable the test, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>
+ and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument
+ <constant>GL_STENCIL_TEST</constant>; to control it, call
+ <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> or
+ <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>.
+ </para>
+ <para>
+ There can be two separate sets of <parameter>sfail</parameter>, <parameter>dpfail</parameter>, and
+ <parameter>dppass</parameter> parameters; one affects back-facing polygons, and the other
+ affects front-facing polygons as well as other non-polygon primitives.
+ <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> sets both front
+ and back stencil state to the same values, as if
+ <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry> were called
+ with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>.
+ </para>
+ <para>
+ <function>glStencilOpSeparate</function> takes three arguments that indicate what happens
+ to the stored stencil value while stenciling is enabled.
+ If the stencil test fails,
+ no change is made to the pixel's color or depth buffers,
+ and <parameter>sfail</parameter> specifies what happens to the stencil buffer contents.
+ The following eight actions are possible.
+ </para>
+ <variablelist>
+ <varlistentry>
+ <term><constant>GL_KEEP</constant></term>
+ <listitem>
+ <para>
+ Keeps the current value.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_ZERO</constant></term>
+ <listitem>
+ <para>
+ Sets the stencil buffer value to 0.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_REPLACE</constant></term>
+ <listitem>
+ <para>
+ Sets the stencil buffer value to <emphasis>ref</emphasis>,
+ as specified by <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_INCR</constant></term>
+ <listitem>
+ <para>
+ Increments the current stencil buffer value.
+ Clamps to the maximum representable unsigned value.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_INCR_WRAP</constant></term>
+ <listitem>
+ <para>
+ Increments the current stencil buffer value.
+ Wraps stencil buffer value to zero when incrementing the maximum
+ representable unsigned value.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_DECR</constant></term>
+ <listitem>
+ <para>
+ Decrements the current stencil buffer value.
+ Clamps to 0.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_DECR_WRAP</constant></term>
+ <listitem>
+ <para>
+ Decrements the current stencil buffer value.
+ Wraps stencil buffer value to the maximum representable unsigned value when
+ decrementing a stencil buffer value of zero.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_INVERT</constant></term>
+ <listitem>
+ <para>
+ Bitwise inverts the current stencil buffer value.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ <para>
+ Stencil buffer values are treated as unsigned integers.
+ When incremented and decremented,
+ values are clamped to 0 and
+ <inlineequation><mml:math>
+ <!-- eqn: 2 sup n - 1:-->
+ <mml:mrow>
+ <mml:msup><mml:mn>2</mml:mn>
+ <mml:mi mathvariant="italic">n</mml:mi>
+ </mml:msup>
+ <mml:mo>-</mml:mo>
+ <mml:mn>1</mml:mn>
+ </mml:mrow>
+ </mml:math></inlineequation>,
+ where
+ <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
+ is the value returned by querying <constant>GL_STENCIL_BITS</constant>.
+ </para>
+ <para>
+ The other two arguments to <function>glStencilOpSeparate</function> specify stencil buffer actions
+ that depend on whether subsequent depth buffer tests succeed (<parameter>dppass</parameter>)
+ or fail (<parameter>dpfail</parameter>) (see
+ <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>).
+ The actions are specified using the same eight symbolic constants as <parameter>sfail</parameter>.
+ Note that <parameter>dpfail</parameter> is ignored when there is no depth buffer,
+ or when the depth buffer is not enabled.
+ In these cases, <parameter>sfail</parameter> and <parameter>dppass</parameter> specify stencil action when the
+ stencil test fails and passes,
+ respectively.
+ </para>
+ </refsect1>
+ <refsect1 id="notes"><title>Notes</title>
+ <para>
+ Initially the stencil test is disabled.
+ If there is no stencil buffer,
+ no stencil modification can occur
+ and it is as if the stencil test always passes.
+ </para>
+ </refsect1>
+ <refsect1 id="errors"><title>Errors</title>
+ <para>
+ <constant>GL_INVALID_ENUM</constant> is generated if <parameter>face</parameter> is any value
+ other than <constant>GL_FRONT</constant>, <constant>GL_BACK</constant>, or <constant>GL_FRONT_AND_BACK</constant>.
+ </para>
+ <para>
+ <constant>GL_INVALID_ENUM</constant> is generated if <parameter>sfail</parameter>,
+ <parameter>dpfail</parameter>, or <parameter>dppass</parameter> is any value other than the eight defined constant values.
+ </para>
+ </refsect1>
+ <refsect1 id="associatedgets"><title>Associated Gets</title>
+ <para>
+ <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument
+ <constant>GL_STENCIL_FAIL</constant>, <constant>GL_STENCIL_PASS_DEPTH_PASS</constant>,
+ <constant>GL_STENCIL_PASS_DEPTH_FAIL</constant>, <constant>GL_STENCIL_BACK_FAIL</constant>,
+ <constant>GL_STENCIL_BACK_PASS_DEPTH_PASS</constant>, <constant>GL_STENCIL_BACK_PASS_DEPTH_FAIL</constant>,
+ or <constant>GL_STENCIL_BITS</constant>
+ </para>
+ <para>
+ <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_TEST</constant>
+ </para>
+ </refsect1>
+ <refsect1 id="seealso"><title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>
+ </para>
+ </refsect1>
+ <refsect1 id="Copyright"><title>Copyright</title>
+ <para>
+ Copyright <trademark class="copyright"></trademark> 2006 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.
+ <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
+ </para>
+ </refsect1>
+</refentry>
HCoop / clinton / guile-figl.git / blobdiff