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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd">
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+<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><link rel="stylesheet" type="text/css" href="opengl-man.css" /><title>glStencilFunc - OpenGL 4 Reference Pages</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glStencilFunc"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glStencilFunc — set front and back function and reference value for stencil testing</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glStencilFunc</b>(</code></td><td>GLenum </td><td><var class="pdparam">func</var>, </td></tr><tr><td> </td><td>GLint </td><td><var class="pdparam">ref</var>, </td></tr><tr><td> </td><td>GLuint </td><td><var class="pdparam">mask</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>func</code></em></span></dt><dd><p>
+ Specifies the test function.
+ Eight symbolic constants are valid:
+ <code class="constant">GL_NEVER</code>,
+ <code class="constant">GL_LESS</code>,
+ <code class="constant">GL_LEQUAL</code>,
+ <code class="constant">GL_GREATER</code>,
+ <code class="constant">GL_GEQUAL</code>,
+ <code class="constant">GL_EQUAL</code>,
+ <code class="constant">GL_NOTEQUAL</code>, and
+ <code class="constant">GL_ALWAYS</code>. The initial value is <code class="constant">GL_ALWAYS</code>.
+ </p></dd><dt><span class="term"><em class="parameter"><code>ref</code></em></span></dt><dd><p>
+ Specifies the reference value for the stencil test.
+ <em class="parameter"><code>ref</code></em> is clamped to the range
+ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
+
+ <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>,
+ where
+ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math>
+ is the number of bitplanes in the stencil buffer. The
+ initial value is 0.
+ </p></dd><dt><span class="term"><em class="parameter"><code>mask</code></em></span></dt><dd><p>
+ 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.
+ </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
+ 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.
+ </p><p>
+ 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 <a href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and <a href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a>
+ with argument <code class="constant">GL_STENCIL_TEST</code>.
+ To specify actions based on the outcome of the stencil test, call
+ <a href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> or
+ <a href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a>.
+ </p><p>
+ There can be two separate sets of <em class="parameter"><code>func</code></em>, <em class="parameter"><code>ref</code></em>, and
+ <em class="parameter"><code>mask</code></em> parameters; one affects back-facing polygons, and the other
+ affects front-facing polygons as well as other non-polygon primitives.
+ <a href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> sets both front
+ and back stencil state to the same values. Use <a href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>
+ to set front and back stencil state to different values.
+ </p><p>
+ <em class="parameter"><code>func</code></em> is a symbolic constant that determines the stencil comparison function.
+ It accepts one of eight values,
+ shown in the following list.
+ <em class="parameter"><code>ref</code></em> is an integer reference value that is used in the stencil comparison.
+ It is clamped to the range
+ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
+
+ <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>,
+ where
+ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math>
+ is the number of bitplanes in the stencil buffer.
+ <em class="parameter"><code>mask</code></em> is bitwise ANDed with both the reference value
+ and the stored stencil value,
+ with the ANDed values participating in the comparison.
+ </p><p>
+ If <span class="emphasis"><em>stencil</em></span> 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 <em class="parameter"><code>func</code></em>.
+ Only if the comparison succeeds is the pixel passed through
+ to the next stage in the rasterization process
+ (see <a href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a>).
+ All tests treat <span class="emphasis"><em>stencil</em></span> values as unsigned integers in the range
+ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
+
+ <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>,
+ where
+ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math>
+ is the number of bitplanes in the stencil buffer.
+ </p><p>
+ The following values are accepted by <em class="parameter"><code>func</code></em>:
+ </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_NEVER</code></span></dt><dd><p>
+ Always fails.
+ </p></dd><dt><span class="term"><code class="constant">GL_LESS</code></span></dt><dd><p>
+ Passes if ( <em class="parameter"><code>ref</code></em> & <em class="parameter"><code>mask</code></em> ) < ( <span class="emphasis"><em>stencil</em></span> & <em class="parameter"><code>mask</code></em> ).
+ </p></dd><dt><span class="term"><code class="constant">GL_LEQUAL</code></span></dt><dd><p>
+ Passes if ( <em class="parameter"><code>ref</code></em> & <em class="parameter"><code>mask</code></em> ) <= ( <span class="emphasis"><em>stencil</em></span> & <em class="parameter"><code>mask</code></em> ).
+ </p></dd><dt><span class="term"><code class="constant">GL_GREATER</code></span></dt><dd><p>
+ Passes if ( <em class="parameter"><code>ref</code></em> & <em class="parameter"><code>mask</code></em> ) > ( <span class="emphasis"><em>stencil</em></span> & <em class="parameter"><code>mask</code></em> ).
+ </p></dd><dt><span class="term"><code class="constant">GL_GEQUAL</code></span></dt><dd><p>
+ Passes if ( <em class="parameter"><code>ref</code></em> & <em class="parameter"><code>mask</code></em> ) >= ( <span class="emphasis"><em>stencil</em></span> & <em class="parameter"><code>mask</code></em> ).
+ </p></dd><dt><span class="term"><code class="constant">GL_EQUAL</code></span></dt><dd><p>
+ Passes if ( <em class="parameter"><code>ref</code></em> & <em class="parameter"><code>mask</code></em> ) = ( <span class="emphasis"><em>stencil</em></span> & <em class="parameter"><code>mask</code></em> ).
+ </p></dd><dt><span class="term"><code class="constant">GL_NOTEQUAL</code></span></dt><dd><p>
+ Passes if ( <em class="parameter"><code>ref</code></em> & <em class="parameter"><code>mask</code></em> ) != ( <span class="emphasis"><em>stencil</em></span> & <em class="parameter"><code>mask</code></em> ).
+ </p></dd><dt><span class="term"><code class="constant">GL_ALWAYS</code></span></dt><dd><p>
+ Always passes.
+ </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
+ 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.
+ </p><p>
+ <a href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> is the same as
+ calling <a href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>
+ with <em class="parameter"><code>face</code></em> set to <code class="constant">GL_FRONT_AND_BACK</code>.
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>
+ <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>func</code></em> is not one of the eight
+ accepted values.
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
+ <a href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument
+ <code class="constant">GL_STENCIL_FUNC</code>, <code class="constant">GL_STENCIL_VALUE_MASK</code>,
+ <code class="constant">GL_STENCIL_REF</code>, <code class="constant">GL_STENCIL_BACK_FUNC</code>,
+ <code class="constant">GL_STENCIL_BACK_VALUE_MASK</code>, <code class="constant">GL_STENCIL_BACK_REF</code>,
+ or <code class="constant">GL_STENCIL_BITS</code>
+ </p><p>
+ <a href="glIsEnabled.xml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument <code class="constant">GL_STENCIL_TEST</code>
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
+ <a href="glBlendFunc.xml"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a>,
+ <a href="glDepthFunc.xml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>,
+ <a href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
+ <a href="glLogicOp.xml"><span class="citerefentry"><span class="refentrytitle">glLogicOp</span></span></a>,
+ <a href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>,
+ <a href="glStencilMask.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMask</span></span></a>,
+ <a href="glStencilMaskSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMaskSeparate</span></span></a>,
+ <a href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a>,
+ <a href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a>
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
+ Copyright <span class="trademark"></span>© 1991-2006
+ Silicon Graphics, Inc. This document is licensed under the SGI
+ Free Software B License. For details, see
+ <a href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
+ </p></div></div></body></html>
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