Commit | Line | Data |
---|---|---|
7faf1d71 AW |
1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd"> | |
4 | <refentry id="glStencilFunc"> | |
5 | <refmeta> | |
6 | <refmetainfo> | |
7 | <copyright> | |
8 | <year>1991-2006</year> | |
9 | <holder>Silicon Graphics, Inc.</holder> | |
10 | </copyright> | |
11 | </refmetainfo> | |
12 | <refentrytitle>glStencilFunc</refentrytitle> | |
13 | <manvolnum>3G</manvolnum> | |
14 | </refmeta> | |
15 | <refnamediv> | |
16 | <refname>glStencilFunc</refname> | |
17 | <refpurpose>set front and back function and reference value for stencil testing</refpurpose> | |
18 | </refnamediv> | |
19 | <!-- eqn: ignoring delim $$ --> | |
20 | <refsynopsisdiv><title>C Specification</title> | |
21 | <funcsynopsis> | |
22 | <funcprototype> | |
23 | <funcdef>void <function>glStencilFunc</function></funcdef> | |
24 | <paramdef>GLenum <parameter>func</parameter></paramdef> | |
25 | <paramdef>GLint <parameter>ref</parameter></paramdef> | |
26 | <paramdef>GLuint <parameter>mask</parameter></paramdef> | |
27 | </funcprototype> | |
28 | </funcsynopsis> | |
29 | </refsynopsisdiv> | |
30 | <refsect1 id="parameters"><title>Parameters</title> | |
31 | <variablelist> | |
32 | <varlistentry> | |
33 | <term><parameter>func</parameter></term> | |
34 | <listitem> | |
35 | <para> | |
36 | Specifies the test function. | |
37 | Eight symbolic constants are valid: | |
38 | <constant>GL_NEVER</constant>, | |
39 | <constant>GL_LESS</constant>, | |
40 | <constant>GL_LEQUAL</constant>, | |
41 | <constant>GL_GREATER</constant>, | |
42 | <constant>GL_GEQUAL</constant>, | |
43 | <constant>GL_EQUAL</constant>, | |
44 | <constant>GL_NOTEQUAL</constant>, and | |
45 | <constant>GL_ALWAYS</constant>. The initial value is <constant>GL_ALWAYS</constant>. | |
46 | </para> | |
47 | </listitem> | |
48 | </varlistentry> | |
49 | <varlistentry> | |
50 | <term><parameter>ref</parameter></term> | |
51 | <listitem> | |
52 | <para> | |
53 | Specifies the reference value for the stencil test. | |
54 | <parameter>ref</parameter> is clamped to the range | |
55 | <inlineequation><mml:math> | |
56 | <!-- eqn: [0, 2 sup n - 1]:--> | |
57 | <mml:mfenced open="[" close="]"> | |
58 | <mml:mn>0</mml:mn> | |
59 | <mml:mrow> | |
60 | <mml:msup><mml:mn>2</mml:mn> | |
61 | <mml:mi mathvariant="italic">n</mml:mi> | |
62 | </mml:msup> | |
63 | <mml:mo>-</mml:mo> | |
64 | <mml:mn>1</mml:mn> | |
65 | </mml:mrow> | |
66 | </mml:mfenced> | |
67 | </mml:math></inlineequation>, | |
68 | where | |
69 | <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation> | |
70 | is the number of bitplanes in the stencil buffer. The | |
71 | initial value is 0. | |
72 | </para> | |
73 | </listitem> | |
74 | </varlistentry> | |
75 | <varlistentry> | |
76 | <term><parameter>mask</parameter></term> | |
77 | <listitem> | |
78 | <para> | |
79 | Specifies a mask that is ANDed with both the reference value | |
80 | and the stored stencil value when the test is done. The initial value | |
81 | is all 1's. | |
82 | </para> | |
83 | </listitem> | |
84 | </varlistentry> | |
85 | </variablelist> | |
86 | </refsect1> | |
87 | <refsect1 id="description"><title>Description</title> | |
88 | <para> | |
89 | Stenciling, | |
90 | like depth-buffering, | |
91 | enables and disables drawing on a per-pixel basis. | |
92 | Stencil planes are first drawn into using GL drawing primitives, then | |
93 | geometry and images are rendered using the stencil planes to mask out | |
94 | portions of the screen. | |
95 | Stenciling is typically used in multipass rendering algorithms | |
96 | to achieve special effects, | |
97 | such as decals, | |
98 | outlining, | |
99 | and constructive solid geometry rendering. | |
100 | </para> | |
101 | <para> | |
102 | The stencil test conditionally eliminates a pixel based on the outcome | |
103 | of a comparison between the reference value | |
104 | and the value in the stencil buffer. | |
105 | To enable and disable the test, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> | |
106 | with argument <constant>GL_STENCIL_TEST</constant>. | |
107 | To specify actions based on the outcome of the stencil test, call | |
108 | <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> or | |
109 | <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>. | |
110 | </para> | |
111 | <para> | |
112 | There can be two separate sets of <parameter>func</parameter>, <parameter>ref</parameter>, and | |
113 | <parameter>mask</parameter> parameters; one affects back-facing polygons, and the other | |
114 | affects front-facing polygons as well as other non-polygon primitives. | |
115 | <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> sets both front | |
116 | and back stencil state to the same values. Use <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry> | |
117 | to set front and back stencil state to different values. | |
118 | </para> | |
119 | <para> | |
120 | <parameter>func</parameter> is a symbolic constant that determines the stencil comparison function. | |
121 | It accepts one of eight values, | |
122 | shown in the following list. | |
123 | <parameter>ref</parameter> is an integer reference value that is used in the stencil comparison. | |
124 | It is clamped to the range | |
125 | <inlineequation><mml:math> | |
126 | <!-- eqn: [0, 2 sup n - 1]:--> | |
127 | <mml:mfenced open="[" close="]"> | |
128 | <mml:mn>0</mml:mn> | |
129 | <mml:mrow> | |
130 | <mml:msup><mml:mn>2</mml:mn> | |
131 | <mml:mi mathvariant="italic">n</mml:mi> | |
132 | </mml:msup> | |
133 | <mml:mo>-</mml:mo> | |
134 | <mml:mn>1</mml:mn> | |
135 | </mml:mrow> | |
136 | </mml:mfenced> | |
137 | </mml:math></inlineequation>, | |
138 | where | |
139 | <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation> | |
140 | is the number of bitplanes in the stencil buffer. | |
141 | <parameter>mask</parameter> is bitwise ANDed with both the reference value | |
142 | and the stored stencil value, | |
143 | with the ANDed values participating in the comparison. | |
144 | </para> | |
145 | <para> | |
146 | If <emphasis>stencil</emphasis> represents the value stored in the corresponding | |
147 | stencil buffer location, | |
148 | the following list shows the effect of each comparison function | |
149 | that can be specified by <parameter>func</parameter>. | |
150 | Only if the comparison succeeds is the pixel passed through | |
151 | to the next stage in the rasterization process | |
152 | (see <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>). | |
153 | All tests treat <emphasis>stencil</emphasis> values as unsigned integers in the range | |
154 | <inlineequation><mml:math> | |
155 | <!-- eqn: [0, 2 sup n - 1]:--> | |
156 | <mml:mfenced open="[" close="]"> | |
157 | <mml:mn>0</mml:mn> | |
158 | <mml:mrow> | |
159 | <mml:msup><mml:mn>2</mml:mn> | |
160 | <mml:mi mathvariant="italic">n</mml:mi> | |
161 | </mml:msup> | |
162 | <mml:mo>-</mml:mo> | |
163 | <mml:mn>1</mml:mn> | |
164 | </mml:mrow> | |
165 | </mml:mfenced> | |
166 | </mml:math></inlineequation>, | |
167 | where | |
168 | <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation> | |
169 | is the number of bitplanes in the stencil buffer. | |
170 | </para> | |
171 | <para> | |
172 | The following values are accepted by <parameter>func</parameter>: | |
173 | </para> | |
174 | <variablelist> | |
175 | <varlistentry> | |
176 | <term><constant>GL_NEVER</constant></term> | |
177 | <listitem> | |
178 | <para> | |
179 | Always fails. | |
180 | </para> | |
181 | </listitem> | |
182 | </varlistentry> | |
183 | <varlistentry> | |
184 | <term><constant>GL_LESS</constant></term> | |
185 | <listitem> | |
186 | <para> | |
187 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) < ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). | |
188 | </para> | |
189 | </listitem> | |
190 | </varlistentry> | |
191 | <varlistentry> | |
192 | <term><constant>GL_LEQUAL</constant></term> | |
193 | <listitem> | |
194 | <para> | |
195 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) <= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). | |
196 | </para> | |
197 | </listitem> | |
198 | </varlistentry> | |
199 | <varlistentry> | |
200 | <term><constant>GL_GREATER</constant></term> | |
201 | <listitem> | |
202 | <para> | |
203 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) > ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). | |
204 | </para> | |
205 | </listitem> | |
206 | </varlistentry> | |
207 | <varlistentry> | |
208 | <term><constant>GL_GEQUAL</constant></term> | |
209 | <listitem> | |
210 | <para> | |
211 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) >= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). | |
212 | </para> | |
213 | </listitem> | |
214 | </varlistentry> | |
215 | <varlistentry> | |
216 | <term><constant>GL_EQUAL</constant></term> | |
217 | <listitem> | |
218 | <para> | |
219 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) = ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). | |
220 | </para> | |
221 | </listitem> | |
222 | </varlistentry> | |
223 | <varlistentry> | |
224 | <term><constant>GL_NOTEQUAL</constant></term> | |
225 | <listitem> | |
226 | <para> | |
227 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) != ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). | |
228 | </para> | |
229 | </listitem> | |
230 | </varlistentry> | |
231 | <varlistentry> | |
232 | <term><constant>GL_ALWAYS</constant></term> | |
233 | <listitem> | |
234 | <para> | |
235 | Always passes. | |
236 | </para> | |
237 | </listitem> | |
238 | </varlistentry> | |
239 | </variablelist> | |
240 | </refsect1> | |
241 | <refsect1 id="notes"><title>Notes</title> | |
242 | <para> | |
243 | Initially, the stencil test is disabled. | |
244 | If there is no stencil buffer, | |
245 | no stencil modification can occur and it is as if | |
246 | the stencil test always passes. | |
247 | </para> | |
248 | <para> | |
249 | <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> is the same as | |
250 | calling <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry> | |
251 | with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>. | |
252 | </para> | |
253 | </refsect1> | |
254 | <refsect1 id="errors"><title>Errors</title> | |
255 | <para> | |
256 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>func</parameter> is not one of the eight | |
257 | accepted values. | |
258 | </para> | |
259 | <para> | |
260 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glStencilFunc</function> | |
261 | is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> | |
262 | and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. | |
263 | </para> | |
264 | </refsect1> | |
265 | <refsect1 id="associatedgets"><title>Associated Gets</title> | |
266 | <para> | |
267 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument | |
268 | <constant>GL_STENCIL_FUNC</constant>, <constant>GL_STENCIL_VALUE_MASK</constant>, | |
269 | <constant>GL_STENCIL_REF</constant>, <constant>GL_STENCIL_BACK_FUNC</constant>, | |
270 | <constant>GL_STENCIL_BACK_VALUE_MASK</constant>, <constant>GL_STENCIL_BACK_REF</constant>, | |
271 | or <constant>GL_STENCIL_BITS</constant> | |
272 | </para> | |
273 | <para> | |
274 | <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_TEST</constant> | |
275 | </para> | |
276 | </refsect1> | |
277 | <refsect1 id="seealso"><title>See Also</title> | |
278 | <para> | |
279 | <citerefentry><refentrytitle>glAlphaFunc</refentrytitle></citerefentry>, | |
280 | <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>, | |
281 | <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>, | |
282 | <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>, | |
283 | <citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>, | |
284 | <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>, | |
285 | <citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>, | |
286 | <citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>, | |
287 | <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>, | |
288 | <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry> | |
289 | </para> | |
290 | </refsect1> | |
291 | <refsect1 id="Copyright"><title>Copyright</title> | |
292 | <para> | |
293 | Copyright <trademark class="copyright"></trademark> 1991-2006 | |
294 | Silicon Graphics, Inc. This document is licensed under the SGI | |
295 | Free Software B License. For details, see | |
296 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. | |
297 | </para> | |
298 | </refsect1> | |
299 | </refentry> |