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1 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> |
2 | <!-- saved from url=(0013)about:internet --> | |
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>glStencilFunc</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></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> | |
4 | Specifies the test function. | |
5 | Eight symbolic constants are valid: | |
6 | <code class="constant">GL_NEVER</code>, | |
7 | <code class="constant">GL_LESS</code>, | |
8 | <code class="constant">GL_LEQUAL</code>, | |
9 | <code class="constant">GL_GREATER</code>, | |
10 | <code class="constant">GL_GEQUAL</code>, | |
11 | <code class="constant">GL_EQUAL</code>, | |
12 | <code class="constant">GL_NOTEQUAL</code>, and | |
13 | <code class="constant">GL_ALWAYS</code>. The initial value is <code class="constant">GL_ALWAYS</code>. | |
14 | </p></dd><dt><span class="term"><em class="parameter"><code>ref</code></em></span></dt><dd><p> | |
15 | Specifies the reference value for the stencil test. | |
16 | <em class="parameter"><code>ref</code></em> is clamped to the range | |
17 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
18 | ||
19 | <mml:mfenced open="[" close="]"> | |
20 | <mml:mn>0</mml:mn> | |
21 | <mml:mrow> | |
22 | <mml:msup><mml:mn>2</mml:mn> | |
23 | <mml:mi mathvariant="italic">n</mml:mi> | |
24 | </mml:msup> | |
25 | <mml:mo>-</mml:mo> | |
26 | <mml:mn>1</mml:mn> | |
27 | </mml:mrow> | |
28 | </mml:mfenced> | |
29 | </mml:math>, | |
30 | where | |
31 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math> | |
32 | is the number of bitplanes in the stencil buffer. The | |
33 | initial value is 0. | |
34 | </p></dd><dt><span class="term"><em class="parameter"><code>mask</code></em></span></dt><dd><p> | |
35 | Specifies a mask that is ANDed with both the reference value | |
36 | and the stored stencil value when the test is done. The initial value | |
37 | is all 1's. | |
38 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p> | |
39 | Stenciling, | |
40 | like depth-buffering, | |
41 | enables and disables drawing on a per-pixel basis. | |
42 | Stencil planes are first drawn into using GL drawing primitives, then | |
43 | geometry and images are rendered using the stencil planes to mask out | |
44 | portions of the screen. | |
45 | Stenciling is typically used in multipass rendering algorithms | |
46 | to achieve special effects, | |
47 | such as decals, | |
48 | outlining, | |
49 | and constructive solid geometry rendering. | |
50 | </p><p> | |
51 | The stencil test conditionally eliminates a pixel based on the outcome | |
52 | of a comparison between the reference value | |
53 | and the value in the stencil buffer. | |
54 | 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> | |
55 | with argument <code class="constant">GL_STENCIL_TEST</code>. | |
56 | To specify actions based on the outcome of the stencil test, call | |
57 | <a class="citerefentry" href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a> or | |
58 | <a class="citerefentry" href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a>. | |
59 | </p><p> | |
60 | There can be two separate sets of <em class="parameter"><code>func</code></em>, <em class="parameter"><code>ref</code></em>, and | |
61 | <em class="parameter"><code>mask</code></em> parameters; one affects back-facing polygons, and the other | |
62 | affects front-facing polygons as well as other non-polygon primitives. | |
63 | <a class="citerefentry" href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> sets both front | |
64 | and back stencil state to the same values. Use <a class="citerefentry" href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a> | |
65 | to set front and back stencil state to different values. | |
66 | </p><p> | |
67 | <em class="parameter"><code>func</code></em> is a symbolic constant that determines the stencil comparison function. | |
68 | It accepts one of eight values, | |
69 | shown in the following list. | |
70 | <em class="parameter"><code>ref</code></em> is an integer reference value that is used in the stencil comparison. | |
71 | It is clamped to the range | |
72 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
73 | ||
74 | <mml:mfenced open="[" close="]"> | |
75 | <mml:mn>0</mml:mn> | |
76 | <mml:mrow> | |
77 | <mml:msup><mml:mn>2</mml:mn> | |
78 | <mml:mi mathvariant="italic">n</mml:mi> | |
79 | </mml:msup> | |
80 | <mml:mo>-</mml:mo> | |
81 | <mml:mn>1</mml:mn> | |
82 | </mml:mrow> | |
83 | </mml:mfenced> | |
84 | </mml:math>, | |
85 | where | |
86 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math> | |
87 | is the number of bitplanes in the stencil buffer. | |
88 | <em class="parameter"><code>mask</code></em> is bitwise ANDed with both the reference value | |
89 | and the stored stencil value, | |
90 | with the ANDed values participating in the comparison. | |
91 | </p><p> | |
92 | If <span class="emphasis"><em>stencil</em></span> represents the value stored in the corresponding | |
93 | stencil buffer location, | |
94 | the following list shows the effect of each comparison function | |
95 | that can be specified by <em class="parameter"><code>func</code></em>. | |
96 | Only if the comparison succeeds is the pixel passed through | |
97 | to the next stage in the rasterization process | |
98 | (see <a class="citerefentry" href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a>). | |
99 | All tests treat <span class="emphasis"><em>stencil</em></span> values as unsigned integers in the range | |
100 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
101 | ||
102 | <mml:mfenced open="[" close="]"> | |
103 | <mml:mn>0</mml:mn> | |
104 | <mml:mrow> | |
105 | <mml:msup><mml:mn>2</mml:mn> | |
106 | <mml:mi mathvariant="italic">n</mml:mi> | |
107 | </mml:msup> | |
108 | <mml:mo>-</mml:mo> | |
109 | <mml:mn>1</mml:mn> | |
110 | </mml:mrow> | |
111 | </mml:mfenced> | |
112 | </mml:math>, | |
113 | where | |
114 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">n</mml:mi></mml:math> | |
115 | is the number of bitplanes in the stencil buffer. | |
116 | </p><p> | |
117 | The following values are accepted by <em class="parameter"><code>func</code></em>: | |
118 | </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_NEVER</code></span></dt><dd><p> | |
119 | Always fails. | |
120 | </p></dd><dt><span class="term"><code class="constant">GL_LESS</code></span></dt><dd><p> | |
121 | 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> ). | |
122 | </p></dd><dt><span class="term"><code class="constant">GL_LEQUAL</code></span></dt><dd><p> | |
123 | 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> ). | |
124 | </p></dd><dt><span class="term"><code class="constant">GL_GREATER</code></span></dt><dd><p> | |
125 | 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> ). | |
126 | </p></dd><dt><span class="term"><code class="constant">GL_GEQUAL</code></span></dt><dd><p> | |
127 | 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> ). | |
128 | </p></dd><dt><span class="term"><code class="constant">GL_EQUAL</code></span></dt><dd><p> | |
129 | 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> ). | |
130 | </p></dd><dt><span class="term"><code class="constant">GL_NOTEQUAL</code></span></dt><dd><p> | |
131 | 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> ). | |
132 | </p></dd><dt><span class="term"><code class="constant">GL_ALWAYS</code></span></dt><dd><p> | |
133 | Always passes. | |
134 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p> | |
135 | Initially, the stencil test is disabled. | |
136 | If there is no stencil buffer, | |
137 | no stencil modification can occur and it is as if | |
138 | the stencil test always passes. | |
139 | </p><p> | |
140 | <a class="citerefentry" href="glStencilFunc.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a> is the same as | |
141 | calling <a class="citerefentry" href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a> | |
142 | with <em class="parameter"><code>face</code></em> set to <code class="constant">GL_FRONT_AND_BACK</code>. | |
143 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p> | |
144 | <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>func</code></em> is not one of the eight | |
145 | accepted values. | |
146 | </p><p> | |
147 | <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glStencilFunc</code> | |
148 | is executed between the execution of <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a> | |
149 | and the corresponding execution of <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>. | |
150 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p> | |
151 | <a class="citerefentry" href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument | |
152 | <code class="constant">GL_STENCIL_FUNC</code>, <code class="constant">GL_STENCIL_VALUE_MASK</code>, | |
153 | <code class="constant">GL_STENCIL_REF</code>, <code class="constant">GL_STENCIL_BACK_FUNC</code>, | |
154 | <code class="constant">GL_STENCIL_BACK_VALUE_MASK</code>, <code class="constant">GL_STENCIL_BACK_REF</code>, | |
155 | or <code class="constant">GL_STENCIL_BITS</code> | |
156 | </p><p> | |
157 | <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> | |
158 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p> | |
159 | <a class="citerefentry" href="glAlphaFunc.xml"><span class="citerefentry"><span class="refentrytitle">glAlphaFunc</span></span></a>, | |
160 | <a class="citerefentry" href="glBlendFunc.xml"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a>, | |
161 | <a class="citerefentry" href="glDepthFunc.xml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>, | |
162 | <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>, | |
163 | <a class="citerefentry" href="glLogicOp.xml"><span class="citerefentry"><span class="refentrytitle">glLogicOp</span></span></a>, | |
164 | <a class="citerefentry" href="glStencilFuncSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilFuncSeparate</span></span></a>, | |
165 | <a class="citerefentry" href="glStencilMask.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMask</span></span></a>, | |
166 | <a class="citerefentry" href="glStencilMaskSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilMaskSeparate</span></span></a>, | |
167 | <a class="citerefentry" href="glStencilOp.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a>, | |
168 | <a class="citerefentry" href="glStencilOpSeparate.xml"><span class="citerefentry"><span class="refentrytitle">glStencilOpSeparate</span></span></a> | |
169 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p> | |
170 | Copyright <span class="trademark"></span>© 1991-2006 | |
171 | Silicon Graphics, Inc. This document is licensed under the SGI | |
172 | Free Software B License. For details, see | |
173 | <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>. | |
174 | </p></div></div></body></html> |