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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" /><title>glStencilFuncSeparate</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glStencilFuncSeparate"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glStencilFuncSeparate — set front and/or 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">glStencilFuncSeparate</b>(</code></td><td>GLenum  </td><td><var class="pdparam">face</var>, </td></tr><tr><td> </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>face</code></em></span></dt><dd><p>
                    Specifies whether front and/or back stencil state is updated.
                    Three symbolic constants are valid:
                    <code class="constant">GL_FRONT</code>,
                    <code class="constant">GL_BACK</code>, and
                    <code class="constant">GL_FRONT_AND_BACK</code>.
                </p></dd><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.
            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.
        </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 class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and <a class="citerefentry" 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 class="citerefentry" href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> or 
            <a class="citerefentry" 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 class="citerefentry" href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> sets both front
            and back stencil state to the same values, as if 
            <a class="citerefentry" href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a> were called
            with <em class="parameter"><code>face</code></em> set to <code class="constant">GL_FRONT_AND_BACK</code>.
        </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 class="citerefentry" 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> &amp; <em class="parameter"><code>mask</code></em> ) &lt; ( <span class="emphasis"><em>stencil</em></span> &amp; <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> &amp; <em class="parameter"><code>mask</code></em> ) &lt;= ( <span class="emphasis"><em>stencil</em></span> &amp; <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> &amp; <em class="parameter"><code>mask</code></em> ) &gt; ( <span class="emphasis"><em>stencil</em></span> &amp; <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> &amp; <em class="parameter"><code>mask</code></em> ) &gt;= ( <span class="emphasis"><em>stencil</em></span> &amp; <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> &amp; <em class="parameter"><code>mask</code></em> ) = ( <span class="emphasis"><em>stencil</em></span> &amp; <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> &amp; <em class="parameter"><code>mask</code></em> ) != ( <span class="emphasis"><em>stencil</em></span> &amp; <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>
            <code class="function">glStencilFuncSeparate</code> is available only if
            the GL version is 2.0 or greater.
        </p><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></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><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glStencilFuncSeparate</code>
            is executed between the execution of <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>
            and the corresponding execution of <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
            <a class="citerefentry" 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 class="citerefentry" 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 class="citerefentry" href="glAlphaFunc.xml"><span class="citerefentry"><span class="refentrytitle">glAlphaFunc</span></span></a>,
            <a class="citerefentry" href="glBlendFunc.xml"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a>,
            <a class="citerefentry" href="glDepthFunc.xml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>,
            <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
            <a class="citerefentry" href="glLogicOp.xml"><span class="citerefentry"><span class="refentrytitle">glLogicOp</span></span></a>,
            <a class="citerefentry" href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>,
            <a class="citerefentry" href="glStencilMask.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMask</span></span></a>,
            <a class="citerefentry" href="glStencilMaskSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMaskSeparate</span></span></a>,
            <a class="citerefentry" href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a>,
            <a class="citerefentry" 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>© 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.
            <a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
        </p></div></div></body></html>
