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<title>glStencilOpSeparate - OpenGL 4 Reference Pages</title>
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<div class="refentry" id="glStencilOpSeparate">
<div class="titlepage"/>
<div class="refnamediv">
<h2>Name</h2>
<p>glStencilOpSeparate — set front and/or back stencil test actions</p>
</div>
<div class="refsynopsisdiv">
<h2>C Specification</h2>
<div class="funcsynopsis">
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">void <strong class="fsfunc">glStencilOpSeparate</strong>(</code>
</td>
<td>GLenum <var class="pdparam">face</var>, </td>
</tr>
<tr>
<td> </td>
<td>GLenum <var class="pdparam">sfail</var>, </td>
</tr>
<tr>
<td> </td>
<td>GLenum <var class="pdparam">dpfail</var>, </td>
</tr>
<tr>
<td> </td>
<td>GLenum <var class="pdparam">dppass</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
</div>
</div>
<div class="refsect1" id="parameters">
<h2>Parameters</h2>
<div class="variablelist">
<dl class="variablelist">
<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>sfail</code>
</em>
</span>
</dt>
<dd>
<p>
Specifies the action to take when the stencil test fails.
Eight symbolic constants are accepted:
<code class="constant">GL_KEEP</code>,
<code class="constant">GL_ZERO</code>,
<code class="constant">GL_REPLACE</code>,
<code class="constant">GL_INCR</code>,
<code class="constant">GL_INCR_WRAP</code>,
<code class="constant">GL_DECR</code>,
<code class="constant">GL_DECR_WRAP</code>, and
<code class="constant">GL_INVERT</code>. The initial value is <code class="constant">GL_KEEP</code>.
</p>
</dd>
<dt>
<span class="term">
<em class="parameter">
<code>dpfail</code>
</em>
</span>
</dt>
<dd>
<p>
Specifies the stencil action when the stencil test passes,
but the depth test fails.
<em class="parameter"><code>dpfail</code></em> accepts the same symbolic constants as <em class="parameter"><code>sfail</code></em>. The initial value
is <code class="constant">GL_KEEP</code>.
</p>
</dd>
<dt>
<span class="term">
<em class="parameter">
<code>dppass</code>
</em>
</span>
</dt>
<dd>
<p>
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.
<em class="parameter"><code>dppass</code></em> accepts the same symbolic constants as <em class="parameter"><code>sfail</code></em>. The initial value
is <code class="constant">GL_KEEP</code>.
</p>
</dd>
</dl>
</div>
</div>
<div class="refsect1" id="description">
<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 value in the stencil buffer and a
reference value. To enable and disable the test, call <a class="citerefentry" href="glEnable.xhtml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>
and <a class="citerefentry" href="glDisable.xhtml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> with argument
<code class="constant">GL_STENCIL_TEST</code>; to control it, call
<a class="citerefentry" href="glStencilFunc.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> or
<a class="citerefentry" href="glStencilFuncSeparate.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>.
</p>
<p>
There can be two separate sets of <em class="parameter"><code>sfail</code></em>, <em class="parameter"><code>dpfail</code></em>, and
<em class="parameter"><code>dppass</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="glStencilOp.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> sets both front
and back stencil state to the same values, as if
<a class="citerefentry" href="glStencilOpSeparate.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</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>
<code class="function">glStencilOpSeparate</code> 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 <em class="parameter"><code>sfail</code></em> specifies what happens to the stencil buffer contents.
The following eight actions are possible.
</p>
<div class="variablelist">
<dl class="variablelist">
<dt>
<span class="term">
<code class="constant">GL_KEEP</code>
</span>
</dt>
<dd>
<p>
Keeps the current value.
</p>
</dd>
<dt>
<span class="term">
<code class="constant">GL_ZERO</code>
</span>
</dt>
<dd>
<p>
Sets the stencil buffer value to 0.
</p>
</dd>
<dt>
<span class="term">
<code class="constant">GL_REPLACE</code>
</span>
</dt>
<dd>
<p>
Sets the stencil buffer value to <span class="emphasis"><em>ref</em></span>,
as specified by <a class="citerefentry" href="glStencilFunc.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>.
</p>
</dd>
<dt>
<span class="term">
<code class="constant">GL_INCR</code>
</span>
</dt>
<dd>
<p>
Increments the current stencil buffer value.
Clamps to the maximum representable unsigned value.
</p>
</dd>
<dt>
<span class="term">
<code class="constant">GL_INCR_WRAP</code>
</span>
</dt>
<dd>
<p>
Increments the current stencil buffer value.
Wraps stencil buffer value to zero when incrementing the maximum
representable unsigned value.
</p>
</dd>
<dt>
<span class="term">
<code class="constant">GL_DECR</code>
</span>
</dt>
<dd>
<p>
Decrements the current stencil buffer value.
Clamps to 0.
</p>
</dd>
<dt>
<span class="term">
<code class="constant">GL_DECR_WRAP</code>
</span>
</dt>
<dd>
<p>
Decrements the current stencil buffer value.
Wraps stencil buffer value to the maximum representable unsigned value when
decrementing a stencil buffer value of zero.
</p>
</dd>
<dt>
<span class="term">
<code class="constant">GL_INVERT</code>
</span>
</dt>
<dd>
<p>
Bitwise inverts the current stencil buffer value.
</p>
</dd>
</dl>
</div>
<p>
Stencil buffer values are treated as unsigned integers.
When incremented and decremented,
values are clamped to 0 and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<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>,
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 value returned by querying <code class="constant">GL_STENCIL_BITS</code>.
</p>
<p>
The other two arguments to <code class="function">glStencilOpSeparate</code> specify stencil buffer actions
that depend on whether subsequent depth buffer tests succeed (<em class="parameter"><code>dppass</code></em>)
or fail (<em class="parameter"><code>dpfail</code></em>) (see
<a class="citerefentry" href="glDepthFunc.xhtml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>).
The actions are specified using the same eight symbolic constants as <em class="parameter"><code>sfail</code></em>.
Note that <em class="parameter"><code>dpfail</code></em> is ignored when there is no depth buffer,
or when the depth buffer is not enabled.
In these cases, <em class="parameter"><code>sfail</code></em> and <em class="parameter"><code>dppass</code></em> specify stencil action when the
stencil test fails and passes,
respectively.
</p>
</div>
<div class="refsect1" id="notes">
<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>
</div>
<div class="refsect1" id="errors">
<h2>Errors</h2>
<p>
<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>face</code></em> is any value
other than <code class="constant">GL_FRONT</code>, <code class="constant">GL_BACK</code>, or <code class="constant">GL_FRONT_AND_BACK</code>.
</p>
<p>
<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>sfail</code></em>,
<em class="parameter"><code>dpfail</code></em>, or <em class="parameter"><code>dppass</code></em> is any value other than the eight defined constant values.
</p>
</div>
<div class="refsect1" id="associatedgets">
<h2>Associated Gets</h2>
<p>
<a class="citerefentry" href="glGet.xhtml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument
<code class="constant">GL_STENCIL_FAIL</code>, <code class="constant">GL_STENCIL_PASS_DEPTH_PASS</code>,
<code class="constant">GL_STENCIL_PASS_DEPTH_FAIL</code>, <code class="constant">GL_STENCIL_BACK_FAIL</code>,
<code class="constant">GL_STENCIL_BACK_PASS_DEPTH_PASS</code>, <code class="constant">GL_STENCIL_BACK_PASS_DEPTH_FAIL</code>,
or <code class="constant">GL_STENCIL_BITS</code>
</p>
<p>
<a class="citerefentry" href="glIsEnabled.xhtml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument <code class="constant">GL_STENCIL_TEST</code>
</p>
</div>
<div class="refsect1" id="versions">
<h2>Version Support</h2>
<div class="informaltable">
<table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">
<colgroup>
<col style="text-align: left; "/>
<col style="text-align: center; " class="firstvers"/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; " class="lastvers"/>
</colgroup>
<thead>
<tr>
<th style="text-align: left; border-right: 2px solid ; ">
</th>
<th style="text-align: center; border-bottom: 2px solid ; " colspan="12">
<span class="bold"><strong>OpenGL Version</strong></span>
</th>
</tr>
<tr>
<th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>Function / Feature Name</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>2.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>2.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.2</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.3</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.2</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.3</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.4</strong></span>
</th>
<th style="text-align: center; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.5</strong></span>
</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: left; border-right: 2px solid ; ">
<code class="function">glStencilOpSeparate</code>
</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; ">✔</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="refsect1" id="seealso">
<h2>See Also</h2>
<p>
<a class="citerefentry" href="glBlendFunc.xhtml"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a>,
<a class="citerefentry" href="glDepthFunc.xhtml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>,
<a class="citerefentry" href="glEnable.xhtml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
<a class="citerefentry" href="glLogicOp.xhtml"><span class="citerefentry"><span class="refentrytitle">glLogicOp</span></span></a>,
<a class="citerefentry" href="glStencilFunc.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>,
<a class="citerefentry" href="glStencilFuncSeparate.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>,
<a class="citerefentry" href="glStencilMask.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilMask</span></span></a>,
<a class="citerefentry" href="glStencilMaskSeparate.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilMaskSeparate</span></span></a>,
<a class="citerefentry" href="glStencilOp.xhtml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a>
</p>
</div>
<div class="refsect1" id="Copyright">
<h2>Copyright</h2>
<p>
Copyright <span class="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.
<a class="link" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
</p>
</div>
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