upstream-man-pages/man2/xhtml/glStencilOp.xml

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   3 <?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>glStencilOp</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glStencilOp"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glStencilOp — set front and back stencil test actions</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">glStencilOp</b>(</code></td><td>GLenum  </td><td><var class="pdparam">sfail</var>, </td></tr><tr><td> </td><td>GLenum  </td><td><var class="pdparam">dpfail</var>, </td></tr><tr><td> </td><td>GLenum  </td><td><var class="pdparam">dppass</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>sfail</code></em></span></dt><dd><p>
   4                     Specifies the action to take when the stencil test fails.
   5                     Eight symbolic constants are accepted:
   6                     <code class="constant">GL_KEEP</code>,
   7                     <code class="constant">GL_ZERO</code>,
   8                     <code class="constant">GL_REPLACE</code>,
   9                     <code class="constant">GL_INCR</code>,
  10                     <code class="constant">GL_INCR_WRAP</code>,
  11                     <code class="constant">GL_DECR</code>,
  12                     <code class="constant">GL_DECR_WRAP</code>, and
  13                     <code class="constant">GL_INVERT</code>. The initial value is <code class="constant">GL_KEEP</code>.
  14                 </p></dd><dt><span class="term"><em class="parameter"><code>dpfail</code></em></span></dt><dd><p>
  15                     Specifies the stencil action when the stencil test passes,
  16                     but the depth test fails.
  17                     <em class="parameter"><code>dpfail</code></em> accepts the same symbolic constants as <em class="parameter"><code>sfail</code></em>. The initial value
  18                     is <code class="constant">GL_KEEP</code>.
  19                 </p></dd><dt><span class="term"><em class="parameter"><code>dppass</code></em></span></dt><dd><p>
  20                     Specifies the stencil action when both the stencil test and the depth
  21                     test pass, or when the stencil test passes and either there is no
  22                     depth buffer or depth testing is not enabled.
  23                     <em class="parameter"><code>dppass</code></em> accepts the same symbolic constants as <em class="parameter"><code>sfail</code></em>. The initial value
  24                     is <code class="constant">GL_KEEP</code>.
  25                 </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
  26             Stenciling,
  27             like depth-buffering,
  28             enables and disables drawing on a per-pixel basis.
  29             You draw into the stencil planes using GL drawing primitives,
  30             then render geometry and images,
  31             using the stencil planes to mask out portions of the screen.
  32             Stenciling is typically used in multipass rendering algorithms
  33             to achieve special effects,
  34             such as decals,
  35             outlining,
  36             and constructive solid geometry rendering.
  37         </p><p>
  38             The stencil test conditionally eliminates a pixel based on the outcome
  39             of a comparison between the value in the stencil buffer and a
  40             reference value. To enable and disable the test, call <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>
  41             and <a class="citerefentry" href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> with argument
  42             <code class="constant">GL_STENCIL_TEST</code>; to control it, call
  43             <a class="citerefentry" href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> or
  44             <a class="citerefentry" href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>.
  45         </p><p>
  46             There can be two separate sets of <em class="parameter"><code>sfail</code></em>, <em class="parameter"><code>dpfail</code></em>, and
  47             <em class="parameter"><code>dppass</code></em> parameters; one affects back-facing polygons, and the other
  48             affects front-facing polygons as well as other non-polygon primitives.
  49             <a class="citerefentry" href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> sets both front
  50             and back stencil state to the same values. Use <a class="citerefentry" href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a>
  51             to set front and back stencil state to different values.
  52         </p><p>
  53             <code class="function">glStencilOp</code> takes three arguments that indicate what happens
  54             to the stored stencil value while stenciling is enabled.
  55             If the stencil test fails,
  56             no change is made to the pixel's color or depth buffers,
  57             and <em class="parameter"><code>sfail</code></em> specifies what happens to the stencil buffer contents.
  58             The following eight actions are possible.
  59         </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_KEEP</code></span></dt><dd><p>
  60                         Keeps the current value.
  61                     </p></dd><dt><span class="term"><code class="constant">GL_ZERO</code></span></dt><dd><p>
  62                         Sets the stencil buffer value to 0.
  63                     </p></dd><dt><span class="term"><code class="constant">GL_REPLACE</code></span></dt><dd><p>
  64                         Sets the stencil buffer value to <span class="emphasis"><em>ref</em></span>,
  65                         as specified by <a class="citerefentry" href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>.
  66                     </p></dd><dt><span class="term"><code class="constant">GL_INCR</code></span></dt><dd><p>
  67                         Increments the current stencil buffer value.
  68                         Clamps to the maximum representable unsigned value.
  69                     </p></dd><dt><span class="term"><code class="constant">GL_INCR_WRAP</code></span></dt><dd><p>
  70                         Increments the current stencil buffer value.
  71                         Wraps stencil buffer value to zero when incrementing the maximum
  72                         representable unsigned value.
  73                     </p></dd><dt><span class="term"><code class="constant">GL_DECR</code></span></dt><dd><p>
  74                         Decrements the current stencil buffer value.
  75                         Clamps to 0.
  76                     </p></dd><dt><span class="term"><code class="constant">GL_DECR_WRAP</code></span></dt><dd><p>
  77                         Decrements the current stencil buffer value.
  78                         Wraps stencil buffer value to the maximum representable unsigned value when
  79                         decrementing a stencil buffer value of zero.
  80                     </p></dd><dt><span class="term"><code class="constant">GL_INVERT</code></span></dt><dd><p>
  81                         Bitwise inverts the current stencil buffer value.
  82                     </p></dd></dl></div><p>
  83             Stencil buffer values are treated as unsigned integers.
  84             When incremented and decremented,
  85             values are clamped to 0 and
  86             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
  87
  88                 <mml:mrow>
  89                     <mml:msup><mml:mn>2</mml:mn>
  90                     <mml:mi mathvariant="italic">n</mml:mi>
  91                     </mml:msup>
  92                     <mml:mo>-</mml:mo>
  93                     <mml:mn>1</mml:mn>
  94                 </mml:mrow>
  95             </mml:math>,
  96             where
  97             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math>
  98             is the value returned by querying <code class="constant">GL_STENCIL_BITS</code>.
  99         </p><p>
 100             The other two arguments to <code class="function">glStencilOp</code> specify stencil buffer actions
 101             that depend on whether subsequent depth buffer tests succeed (<em class="parameter"><code>dppass</code></em>)
 102             or fail (<em class="parameter"><code>dpfail</code></em>) (see
 103             <a class="citerefentry" href="glDepthFunc.xml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>).
 104             The actions are specified using the same eight symbolic constants as <em class="parameter"><code>sfail</code></em>.
 105             Note that <em class="parameter"><code>dpfail</code></em> is ignored when there is no depth buffer,
 106             or when the depth buffer is not enabled.
 107             In these cases, <em class="parameter"><code>sfail</code></em> and <em class="parameter"><code>dppass</code></em> specify stencil action when the
 108             stencil test fails and passes,
 109             respectively.
 110         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
 111             <code class="constant">GL_DECR_WRAP</code> and <code class="constant">GL_INCR_WRAP</code> are available only if the GL
 112             version is 1.4 or greater.
 113         </p><p>
 114             Initially the stencil test is disabled.
 115             If there is no stencil buffer,
 116             no stencil modification can occur
 117             and it is as if the stencil tests always pass,
 118             regardless of any call to <code class="function">glStencilOp</code>.
 119         </p><p>
 120             <a class="citerefentry" href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> is the same as
 121             calling <a class="citerefentry" href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a>
 122             with <em class="parameter"><code>face</code></em> set to <code class="constant">GL_FRONT_AND_BACK</code>.
 123         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>
 124             <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>sfail</code></em>,
 125             <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.
 126         </p><p>
 127             <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glStencilOp</code>
 128             is executed between the execution of <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>
 129             and the corresponding execution of <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.
 130         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
 131             <a class="citerefentry" href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument
 132             <code class="constant">GL_STENCIL_FAIL</code>, <code class="constant">GL_STENCIL_PASS_DEPTH_PASS</code>,
 133             <code class="constant">GL_STENCIL_PASS_DEPTH_FAIL</code>, <code class="constant">GL_STENCIL_BACK_FAIL</code>,
 134             <code class="constant">GL_STENCIL_BACK_PASS_DEPTH_PASS</code>, <code class="constant">GL_STENCIL_BACK_PASS_DEPTH_FAIL</code>,
 135             or <code class="constant">GL_STENCIL_BITS</code>
 136         </p><p>
 137             <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>
 138         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
 139             <a class="citerefentry" href="glAlphaFunc.xml"><span class="citerefentry"><span class="refentrytitle">glAlphaFunc</span></span></a>,
 140             <a class="citerefentry" href="glBlendFunc.xml"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a>,
 141             <a class="citerefentry" href="glDepthFunc.xml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>,
 142             <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
 143             <a class="citerefentry" href="glLogicOp.xml"><span class="citerefentry"><span class="refentrytitle">glLogicOp</span></span></a>,
 144             <a class="citerefentry" href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>,
 145             <a class="citerefentry" href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>,
 146             <a class="citerefentry" href="glStencilMask.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMask</span></span></a>,
 147             <a class="citerefentry" href="glStencilMaskSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMaskSeparate</span></span></a>,
 148             <a class="citerefentry" href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a>
 149         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
 150             Copyright <span class="trademark"></span>© 1991-2006
 151             Silicon Graphics, Inc. This document is licensed under the SGI
 152             Free Software B License. For details, see
 153             <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
 154         </p></div></div></body></html>