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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="glStencilFunc">
+ <refmeta>
+ <refmetainfo>
+ <copyright>
+ <year>1991-2006</year>
+ <holder>Silicon Graphics, Inc.</holder>
+ </copyright>
+ </refmetainfo>
+ <refentrytitle>glStencilFunc</refentrytitle>
+ <manvolnum>3G</manvolnum>
+ </refmeta>
+ <refnamediv>
+ <refname>glStencilFunc</refname>
+ <refpurpose>set front and back function and reference value for stencil testing</refpurpose>
+ </refnamediv>
+ <!-- eqn: ignoring delim $$ -->
+ <refsynopsisdiv><title>C Specification</title>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>void <function>glStencilFunc</function></funcdef>
+ <paramdef>GLenum <parameter>func</parameter></paramdef>
+ <paramdef>GLint <parameter>ref</parameter></paramdef>
+ <paramdef>GLuint <parameter>mask</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+ <refsect1 id="parameters"><title>Parameters</title>
+ <variablelist>
+ <varlistentry>
+ <term><parameter>func</parameter></term>
+ <listitem>
+ <para>
+ Specifies the test function.
+ Eight symbolic constants are valid:
+ <constant>GL_NEVER</constant>,
+ <constant>GL_LESS</constant>,
+ <constant>GL_LEQUAL</constant>,
+ <constant>GL_GREATER</constant>,
+ <constant>GL_GEQUAL</constant>,
+ <constant>GL_EQUAL</constant>,
+ <constant>GL_NOTEQUAL</constant>, and
+ <constant>GL_ALWAYS</constant>. The initial value is <constant>GL_ALWAYS</constant>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>ref</parameter></term>
+ <listitem>
+ <para>
+ Specifies the reference value for the stencil test.
+ <parameter>ref</parameter> is clamped to the range
+ <inlineequation><mml:math>
+ <!-- eqn: [0, 2 sup n - 1]:-->
+ <mml:mfenced open="[" close="]">
+ <mml:mn>0</mml:mn>
+ <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:mfenced>
+ </mml:math></inlineequation>,
+ where
+ <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
+ is the number of bitplanes in the stencil buffer. The
+ initial value is 0.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>mask</parameter></term>
+ <listitem>
+ <para>
+ Specifies a mask that is ANDed with both the reference value
+ and the stored stencil value when the test is done. The initial value
+ is all 1's.
+ </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.
+ Stencil planes are first drawn into using GL drawing primitives, then
+ geometry and images are rendered 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 reference value
+ and the value in the stencil buffer.
+ 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 specify actions based on the outcome of the stencil test, call
+ <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> or
+ <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>.
+ </para>
+ <para>
+ There can be two separate sets of <parameter>func</parameter>, <parameter>ref</parameter>, and
+ <parameter>mask</parameter> parameters; one affects back-facing polygons, and the other
+ affects front-facing polygons as well as other non-polygon primitives.
+ <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> sets both front
+ and back stencil state to the same values. Use <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>
+ to set front and back stencil state to different values.
+ </para>
+ <para>
+ <parameter>func</parameter> is a symbolic constant that determines the stencil comparison function.
+ It accepts one of eight values,
+ shown in the following list.
+ <parameter>ref</parameter> is an integer reference value that is used in the stencil comparison.
+ It is clamped to the range
+ <inlineequation><mml:math>
+ <!-- eqn: [0, 2 sup n - 1]:-->
+ <mml:mfenced open="[" close="]">
+ <mml:mn>0</mml:mn>
+ <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:mfenced>
+ </mml:math></inlineequation>,
+ where
+ <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
+ is the number of bitplanes in the stencil buffer.
+ <parameter>mask</parameter> is bitwise ANDed with both the reference value
+ and the stored stencil value,
+ with the ANDed values participating in the comparison.
+ </para>
+ <para>
+ If <emphasis>stencil</emphasis> represents the value stored in the corresponding
+ stencil buffer location,
+ the following list shows the effect of each comparison function
+ that can be specified by <parameter>func</parameter>.
+ Only if the comparison succeeds is the pixel passed through
+ to the next stage in the rasterization process
+ (see <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>).
+ All tests treat <emphasis>stencil</emphasis> values as unsigned integers in the range
+ <inlineequation><mml:math>
+ <!-- eqn: [0, 2 sup n - 1]:-->
+ <mml:mfenced open="[" close="]">
+ <mml:mn>0</mml:mn>
+ <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:mfenced>
+ </mml:math></inlineequation>,
+ where
+ <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
+ is the number of bitplanes in the stencil buffer.
+ </para>
+ <para>
+ The following values are accepted by <parameter>func</parameter>:
+ </para>
+ <variablelist>
+ <varlistentry>
+ <term><constant>GL_NEVER</constant></term>
+ <listitem>
+ <para>
+ Always fails.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_LESS</constant></term>
+ <listitem>
+ <para>
+ Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) < ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_LEQUAL</constant></term>
+ <listitem>
+ <para>
+ Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) <= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_GREATER</constant></term>
+ <listitem>
+ <para>
+ Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) > ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_GEQUAL</constant></term>
+ <listitem>
+ <para>
+ Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) >= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_EQUAL</constant></term>
+ <listitem>
+ <para>
+ Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) = ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_NOTEQUAL</constant></term>
+ <listitem>
+ <para>
+ Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) != ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GL_ALWAYS</constant></term>
+ <listitem>
+ <para>
+ Always passes.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </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>
+ <para>
+ <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> is the same as
+ calling <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>
+ with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>.
+ </para>
+ </refsect1>
+ <refsect1 id="errors"><title>Errors</title>
+ <para>
+ <constant>GL_INVALID_ENUM</constant> is generated if <parameter>func</parameter> is not one of the eight
+ accepted values.
+ </para>
+ <para>
+ <constant>GL_INVALID_OPERATION</constant> is generated if <function>glStencilFunc</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_STENCIL_FUNC</constant>, <constant>GL_STENCIL_VALUE_MASK</constant>,
+ <constant>GL_STENCIL_REF</constant>, <constant>GL_STENCIL_BACK_FUNC</constant>,
+ <constant>GL_STENCIL_BACK_VALUE_MASK</constant>, <constant>GL_STENCIL_BACK_REF</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>glAlphaFunc</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glStencilOpSeparate</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>
HCoop / clinton / guile-figl.git / blobdiff