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1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> | |
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4 | <?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>glStencilOp - 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="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> | |
5 | Specifies the action to take when the stencil test fails. | |
6 | Eight symbolic constants are accepted: | |
7 | <code class="constant">GL_KEEP</code>, | |
8 | <code class="constant">GL_ZERO</code>, | |
9 | <code class="constant">GL_REPLACE</code>, | |
10 | <code class="constant">GL_INCR</code>, | |
11 | <code class="constant">GL_INCR_WRAP</code>, | |
12 | <code class="constant">GL_DECR</code>, | |
13 | <code class="constant">GL_DECR_WRAP</code>, and | |
14 | <code class="constant">GL_INVERT</code>. The initial value is <code class="constant">GL_KEEP</code>. | |
15 | </p></dd><dt><span class="term"><em class="parameter"><code>dpfail</code></em></span></dt><dd><p> | |
16 | Specifies the stencil action when the stencil test passes, | |
17 | but the depth test fails. | |
18 | <em class="parameter"><code>dpfail</code></em> accepts the same symbolic constants as <em class="parameter"><code>sfail</code></em>. The initial value | |
19 | is <code class="constant">GL_KEEP</code>. | |
20 | </p></dd><dt><span class="term"><em class="parameter"><code>dppass</code></em></span></dt><dd><p> | |
21 | Specifies the stencil action when both the stencil test and the depth | |
22 | test pass, or when the stencil test passes and either there is no | |
23 | depth buffer or depth testing is not enabled. | |
24 | <em class="parameter"><code>dppass</code></em> accepts the same symbolic constants as <em class="parameter"><code>sfail</code></em>. The initial value | |
25 | is <code class="constant">GL_KEEP</code>. | |
26 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p> | |
27 | Stenciling, | |
28 | like depth-buffering, | |
29 | enables and disables drawing on a per-pixel basis. | |
30 | You draw into the stencil planes using GL drawing primitives, | |
31 | then render geometry and images, | |
32 | using the stencil planes to mask out portions of the screen. | |
33 | Stenciling is typically used in multipass rendering algorithms | |
34 | to achieve special effects, | |
35 | such as decals, | |
36 | outlining, | |
37 | and constructive solid geometry rendering. | |
38 | </p><p> | |
39 | The stencil test conditionally eliminates a pixel based on the outcome | |
40 | of a comparison between the value in the stencil buffer and a | |
41 | reference value. To enable and disable the test, call <a href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> | |
42 | and <a href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> with argument | |
43 | <code class="constant">GL_STENCIL_TEST</code>; to control it, call | |
44 | <a href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> or | |
45 | <a href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>. | |
46 | </p><p> | |
47 | There can be two separate sets of <em class="parameter"><code>sfail</code></em>, <em class="parameter"><code>dpfail</code></em>, and | |
48 | <em class="parameter"><code>dppass</code></em> parameters; one affects back-facing polygons, and the other | |
49 | affects front-facing polygons as well as other non-polygon primitives. | |
50 | <a href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> sets both front | |
51 | and back stencil state to the same values. Use <a href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a> | |
52 | to set front and back stencil state to different values. | |
53 | </p><p> | |
54 | <code class="function">glStencilOp</code> takes three arguments that indicate what happens | |
55 | to the stored stencil value while stenciling is enabled. | |
56 | If the stencil test fails, | |
57 | no change is made to the pixel's color or depth buffers, | |
58 | and <em class="parameter"><code>sfail</code></em> specifies what happens to the stencil buffer contents. | |
59 | The following eight actions are possible. | |
60 | </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_KEEP</code></span></dt><dd><p> | |
61 | Keeps the current value. | |
62 | </p></dd><dt><span class="term"><code class="constant">GL_ZERO</code></span></dt><dd><p> | |
63 | Sets the stencil buffer value to 0. | |
64 | </p></dd><dt><span class="term"><code class="constant">GL_REPLACE</code></span></dt><dd><p> | |
65 | Sets the stencil buffer value to <span class="emphasis"><em>ref</em></span>, | |
66 | as specified by <a href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>. | |
67 | </p></dd><dt><span class="term"><code class="constant">GL_INCR</code></span></dt><dd><p> | |
68 | Increments the current stencil buffer value. | |
69 | Clamps to the maximum representable unsigned value. | |
70 | </p></dd><dt><span class="term"><code class="constant">GL_INCR_WRAP</code></span></dt><dd><p> | |
71 | Increments the current stencil buffer value. | |
72 | Wraps stencil buffer value to zero when incrementing the maximum | |
73 | representable unsigned value. | |
74 | </p></dd><dt><span class="term"><code class="constant">GL_DECR</code></span></dt><dd><p> | |
75 | Decrements the current stencil buffer value. | |
76 | Clamps to 0. | |
77 | </p></dd><dt><span class="term"><code class="constant">GL_DECR_WRAP</code></span></dt><dd><p> | |
78 | Decrements the current stencil buffer value. | |
79 | Wraps stencil buffer value to the maximum representable unsigned value when | |
80 | decrementing a stencil buffer value of zero. | |
81 | </p></dd><dt><span class="term"><code class="constant">GL_INVERT</code></span></dt><dd><p> | |
82 | Bitwise inverts the current stencil buffer value. | |
83 | </p></dd></dl></div><p> | |
84 | Stencil buffer values are treated as unsigned integers. | |
85 | When incremented and decremented, | |
86 | values are clamped to 0 and | |
87 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
88 | ||
89 | <mml:mrow> | |
90 | <mml:msup><mml:mn>2</mml:mn> | |
91 | <mml:mi mathvariant="italic">n</mml:mi> | |
92 | </mml:msup> | |
93 | <mml:mo>-</mml:mo> | |
94 | <mml:mn>1</mml:mn> | |
95 | </mml:mrow> | |
96 | </mml:math>, | |
97 | where | |
98 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math> | |
99 | is the value returned by querying <code class="constant">GL_STENCIL_BITS</code>. | |
100 | </p><p> | |
101 | The other two arguments to <code class="function">glStencilOp</code> specify stencil buffer actions | |
102 | that depend on whether subsequent depth buffer tests succeed (<em class="parameter"><code>dppass</code></em>) | |
103 | or fail (<em class="parameter"><code>dpfail</code></em>) (see | |
104 | <a href="glDepthFunc.xml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>). | |
105 | The actions are specified using the same eight symbolic constants as <em class="parameter"><code>sfail</code></em>. | |
106 | Note that <em class="parameter"><code>dpfail</code></em> is ignored when there is no depth buffer, | |
107 | or when the depth buffer is not enabled. | |
108 | In these cases, <em class="parameter"><code>sfail</code></em> and <em class="parameter"><code>dppass</code></em> specify stencil action when the | |
109 | stencil test fails and passes, | |
110 | respectively. | |
111 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p> | |
112 | Initially the stencil test is disabled. | |
113 | If there is no stencil buffer, | |
114 | no stencil modification can occur | |
115 | and it is as if the stencil tests always pass, | |
116 | regardless of any call to <code class="function">glStencilOp</code>. | |
117 | </p><p> | |
118 | <a href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> is the same as | |
119 | calling <a href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a> | |
120 | with <em class="parameter"><code>face</code></em> set to <code class="constant">GL_FRONT_AND_BACK</code>. | |
121 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p> | |
122 | <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>sfail</code></em>, | |
123 | <em class="parameter"><code>dpfail</code></em>, or <em class="parameter"><code>dppass</code></em> is any value other than the defined constant values. | |
124 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p> | |
125 | <a href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument | |
126 | <code class="constant">GL_STENCIL_FAIL</code>, <code class="constant">GL_STENCIL_PASS_DEPTH_PASS</code>, | |
127 | <code class="constant">GL_STENCIL_PASS_DEPTH_FAIL</code>, <code class="constant">GL_STENCIL_BACK_FAIL</code>, | |
128 | <code class="constant">GL_STENCIL_BACK_PASS_DEPTH_PASS</code>, <code class="constant">GL_STENCIL_BACK_PASS_DEPTH_FAIL</code>, | |
129 | or <code class="constant">GL_STENCIL_BITS</code> | |
130 | </p><p> | |
131 | <a href="glIsEnabled.xml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument <code class="constant">GL_STENCIL_TEST</code> | |
132 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p> | |
133 | <a href="glBlendFunc.xml"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a>, | |
134 | <a href="glDepthFunc.xml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>, | |
135 | <a href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>, | |
136 | <a href="glLogicOp.xml"><span class="citerefentry"><span class="refentrytitle">glLogicOp</span></span></a>, | |
137 | <a href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>, | |
138 | <a href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>, | |
139 | <a href="glStencilMask.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMask</span></span></a>, | |
140 | <a href="glStencilMaskSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMaskSeparate</span></span></a>, | |
141 | <a href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a> | |
142 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p> | |
143 | Copyright <span class="trademark"></span>© 1991-2006 | |
144 | Silicon Graphics, Inc. This document is licensed under the SGI | |
145 | Free Software B License. For details, see | |
146 | <a href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>. | |
147 | </p></div></div></body></html> |