| 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="glStencilFuncSeparate"> |
| 5 | <refmeta> |
| 6 | <refmetainfo> |
| 7 | <copyright> |
| 8 | <year>1991-2006</year> |
| 9 | <holder>Silicon Graphics, Inc.</holder> |
| 10 | </copyright> |
| 11 | </refmetainfo> |
| 12 | <refentrytitle>glStencilFuncSeparate</refentrytitle> |
| 13 | <manvolnum>3G</manvolnum> |
| 14 | </refmeta> |
| 15 | <refnamediv> |
| 16 | <refname>glStencilFuncSeparate</refname> |
| 17 | <refpurpose>set front and/or 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>glStencilFuncSeparate</function></funcdef> |
| 24 | <paramdef>GLenum <parameter>face</parameter></paramdef> |
| 25 | <paramdef>GLenum <parameter>func</parameter></paramdef> |
| 26 | <paramdef>GLint <parameter>ref</parameter></paramdef> |
| 27 | <paramdef>GLuint <parameter>mask</parameter></paramdef> |
| 28 | </funcprototype> |
| 29 | </funcsynopsis> |
| 30 | </refsynopsisdiv> |
| 31 | <refsect1 id="parameters"><title>Parameters</title> |
| 32 | <variablelist> |
| 33 | <varlistentry> |
| 34 | <term><parameter>face</parameter></term> |
| 35 | <listitem> |
| 36 | <para> |
| 37 | Specifies whether front and/or back stencil state is updated. |
| 38 | Three symbolic constants are valid: |
| 39 | <constant>GL_FRONT</constant>, |
| 40 | <constant>GL_BACK</constant>, and |
| 41 | <constant>GL_FRONT_AND_BACK</constant>. |
| 42 | </para> |
| 43 | </listitem> |
| 44 | </varlistentry> |
| 45 | <varlistentry> |
| 46 | <term><parameter>func</parameter></term> |
| 47 | <listitem> |
| 48 | <para> |
| 49 | Specifies the test function. |
| 50 | Eight symbolic constants are valid: |
| 51 | <constant>GL_NEVER</constant>, |
| 52 | <constant>GL_LESS</constant>, |
| 53 | <constant>GL_LEQUAL</constant>, |
| 54 | <constant>GL_GREATER</constant>, |
| 55 | <constant>GL_GEQUAL</constant>, |
| 56 | <constant>GL_EQUAL</constant>, |
| 57 | <constant>GL_NOTEQUAL</constant>, and |
| 58 | <constant>GL_ALWAYS</constant>. The initial value is <constant>GL_ALWAYS</constant>. |
| 59 | </para> |
| 60 | </listitem> |
| 61 | </varlistentry> |
| 62 | <varlistentry> |
| 63 | <term><parameter>ref</parameter></term> |
| 64 | <listitem> |
| 65 | <para> |
| 66 | Specifies the reference value for the stencil test. |
| 67 | <parameter>ref</parameter> is clamped to the range |
| 68 | <inlineequation><mml:math> |
| 69 | <!-- eqn: [0, 2 sup n - 1]:--> |
| 70 | <mml:mfenced open="[" close="]"> |
| 71 | <mml:mn>0</mml:mn> |
| 72 | <mml:mrow> |
| 73 | <mml:msup><mml:mn>2</mml:mn> |
| 74 | <mml:mi mathvariant="italic">n</mml:mi> |
| 75 | </mml:msup> |
| 76 | <mml:mo>-</mml:mo> |
| 77 | <mml:mn>1</mml:mn> |
| 78 | </mml:mrow> |
| 79 | </mml:mfenced> |
| 80 | </mml:math></inlineequation>, |
| 81 | where |
| 82 | <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation> |
| 83 | is the number of bitplanes in the stencil buffer. The |
| 84 | initial value is 0. |
| 85 | </para> |
| 86 | </listitem> |
| 87 | </varlistentry> |
| 88 | <varlistentry> |
| 89 | <term><parameter>mask</parameter></term> |
| 90 | <listitem> |
| 91 | <para> |
| 92 | Specifies a mask that is ANDed with both the reference value |
| 93 | and the stored stencil value when the test is done. The initial value |
| 94 | is all 1's. |
| 95 | </para> |
| 96 | </listitem> |
| 97 | </varlistentry> |
| 98 | </variablelist> |
| 99 | </refsect1> |
| 100 | <refsect1 id="description"><title>Description</title> |
| 101 | <para> |
| 102 | Stenciling, |
| 103 | like depth-buffering, |
| 104 | enables and disables drawing on a per-pixel basis. |
| 105 | You draw into the stencil planes using GL drawing primitives, |
| 106 | then render geometry and images, |
| 107 | using the stencil planes to mask out portions of the screen. |
| 108 | Stenciling is typically used in multipass rendering algorithms |
| 109 | to achieve special effects, |
| 110 | such as decals, |
| 111 | outlining, |
| 112 | and constructive solid geometry rendering. |
| 113 | </para> |
| 114 | <para> |
| 115 | The stencil test conditionally eliminates a pixel based on the outcome |
| 116 | of a comparison between the reference value |
| 117 | and the value in the stencil buffer. |
| 118 | To enable and disable the test, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> |
| 119 | with argument <constant>GL_STENCIL_TEST</constant>. |
| 120 | To specify actions based on the outcome of the stencil test, call |
| 121 | <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> or |
| 122 | <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>. |
| 123 | </para> |
| 124 | <para> |
| 125 | There can be two separate sets of <parameter>func</parameter>, <parameter>ref</parameter>, and |
| 126 | <parameter>mask</parameter> parameters; one affects back-facing polygons, and the other |
| 127 | affects front-facing polygons as well as other non-polygon primitives. |
| 128 | <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> sets both front |
| 129 | and back stencil state to the same values, as if |
| 130 | <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry> were called |
| 131 | with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>. |
| 132 | </para> |
| 133 | <para> |
| 134 | <parameter>func</parameter> is a symbolic constant that determines the stencil comparison function. |
| 135 | It accepts one of eight values, |
| 136 | shown in the following list. |
| 137 | <parameter>ref</parameter> is an integer reference value that is used in the stencil comparison. |
| 138 | It is clamped to the range |
| 139 | <inlineequation><mml:math> |
| 140 | <!-- eqn: [0, 2 sup n - 1]:--> |
| 141 | <mml:mfenced open="[" close="]"> |
| 142 | <mml:mn>0</mml:mn> |
| 143 | <mml:mrow> |
| 144 | <mml:msup><mml:mn>2</mml:mn> |
| 145 | <mml:mi mathvariant="italic">n</mml:mi> |
| 146 | </mml:msup> |
| 147 | <mml:mo>-</mml:mo> |
| 148 | <mml:mn>1</mml:mn> |
| 149 | </mml:mrow> |
| 150 | </mml:mfenced> |
| 151 | </mml:math></inlineequation>, |
| 152 | where |
| 153 | <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation> |
| 154 | is the number of bitplanes in the stencil buffer. |
| 155 | <parameter>mask</parameter> is bitwise ANDed with both the reference value |
| 156 | and the stored stencil value, |
| 157 | with the ANDed values participating in the comparison. |
| 158 | </para> |
| 159 | <para> |
| 160 | If <emphasis>stencil</emphasis> represents the value stored in the corresponding |
| 161 | stencil buffer location, |
| 162 | the following list shows the effect of each comparison function |
| 163 | that can be specified by <parameter>func</parameter>. |
| 164 | Only if the comparison succeeds is the pixel passed through |
| 165 | to the next stage in the rasterization process |
| 166 | (see <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>). |
| 167 | All tests treat <emphasis>stencil</emphasis> values as unsigned integers in the range |
| 168 | <inlineequation><mml:math> |
| 169 | <!-- eqn: [0, 2 sup n - 1]:--> |
| 170 | <mml:mfenced open="[" close="]"> |
| 171 | <mml:mn>0</mml:mn> |
| 172 | <mml:mrow> |
| 173 | <mml:msup><mml:mn>2</mml:mn> |
| 174 | <mml:mi mathvariant="italic">n</mml:mi> |
| 175 | </mml:msup> |
| 176 | <mml:mo>-</mml:mo> |
| 177 | <mml:mn>1</mml:mn> |
| 178 | </mml:mrow> |
| 179 | </mml:mfenced> |
| 180 | </mml:math></inlineequation>, |
| 181 | where |
| 182 | <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation> |
| 183 | is the number of bitplanes in the stencil buffer. |
| 184 | </para> |
| 185 | <para> |
| 186 | The following values are accepted by <parameter>func</parameter>: |
| 187 | </para> |
| 188 | <variablelist> |
| 189 | <varlistentry> |
| 190 | <term><constant>GL_NEVER</constant></term> |
| 191 | <listitem> |
| 192 | <para> |
| 193 | Always fails. |
| 194 | </para> |
| 195 | </listitem> |
| 196 | </varlistentry> |
| 197 | <varlistentry> |
| 198 | <term><constant>GL_LESS</constant></term> |
| 199 | <listitem> |
| 200 | <para> |
| 201 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) < ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). |
| 202 | </para> |
| 203 | </listitem> |
| 204 | </varlistentry> |
| 205 | <varlistentry> |
| 206 | <term><constant>GL_LEQUAL</constant></term> |
| 207 | <listitem> |
| 208 | <para> |
| 209 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) <= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). |
| 210 | </para> |
| 211 | </listitem> |
| 212 | </varlistentry> |
| 213 | <varlistentry> |
| 214 | <term><constant>GL_GREATER</constant></term> |
| 215 | <listitem> |
| 216 | <para> |
| 217 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) > ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). |
| 218 | </para> |
| 219 | </listitem> |
| 220 | </varlistentry> |
| 221 | <varlistentry> |
| 222 | <term><constant>GL_GEQUAL</constant></term> |
| 223 | <listitem> |
| 224 | <para> |
| 225 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) >= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). |
| 226 | </para> |
| 227 | </listitem> |
| 228 | </varlistentry> |
| 229 | <varlistentry> |
| 230 | <term><constant>GL_EQUAL</constant></term> |
| 231 | <listitem> |
| 232 | <para> |
| 233 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) = ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). |
| 234 | </para> |
| 235 | </listitem> |
| 236 | </varlistentry> |
| 237 | <varlistentry> |
| 238 | <term><constant>GL_NOTEQUAL</constant></term> |
| 239 | <listitem> |
| 240 | <para> |
| 241 | Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) != ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ). |
| 242 | </para> |
| 243 | </listitem> |
| 244 | </varlistentry> |
| 245 | <varlistentry> |
| 246 | <term><constant>GL_ALWAYS</constant></term> |
| 247 | <listitem> |
| 248 | <para> |
| 249 | Always passes. |
| 250 | </para> |
| 251 | </listitem> |
| 252 | </varlistentry> |
| 253 | </variablelist> |
| 254 | </refsect1> |
| 255 | <refsect1 id="notes"><title>Notes</title> |
| 256 | <para> |
| 257 | <function>glStencilFuncSeparate</function> is available only if |
| 258 | the GL version is 2.0 or greater. |
| 259 | </para> |
| 260 | <para> |
| 261 | Initially, the stencil test is disabled. |
| 262 | If there is no stencil buffer, |
| 263 | no stencil modification can occur and it is as if |
| 264 | the stencil test always passes. |
| 265 | </para> |
| 266 | </refsect1> |
| 267 | <refsect1 id="errors"><title>Errors</title> |
| 268 | <para> |
| 269 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>func</parameter> is not one of the eight |
| 270 | accepted values. |
| 271 | </para> |
| 272 | <para> |
| 273 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glStencilFuncSeparate</function> |
| 274 | is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> |
| 275 | and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. |
| 276 | </para> |
| 277 | </refsect1> |
| 278 | <refsect1 id="associatedgets"><title>Associated Gets</title> |
| 279 | <para> |
| 280 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument |
| 281 | <constant>GL_STENCIL_FUNC</constant>, <constant>GL_STENCIL_VALUE_MASK</constant>, |
| 282 | <constant>GL_STENCIL_REF</constant>, <constant>GL_STENCIL_BACK_FUNC</constant>, |
| 283 | <constant>GL_STENCIL_BACK_VALUE_MASK</constant>, <constant>GL_STENCIL_BACK_REF</constant>, |
| 284 | or <constant>GL_STENCIL_BITS</constant> |
| 285 | </para> |
| 286 | <para> |
| 287 | <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_TEST</constant> |
| 288 | </para> |
| 289 | </refsect1> |
| 290 | <refsect1 id="seealso"><title>See Also</title> |
| 291 | <para> |
| 292 | <citerefentry><refentrytitle>glAlphaFunc</refentrytitle></citerefentry>, |
| 293 | <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>, |
| 294 | <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>, |
| 295 | <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>, |
| 296 | <citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>, |
| 297 | <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>, |
| 298 | <citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>, |
| 299 | <citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>, |
| 300 | <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>, |
| 301 | <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry> |
| 302 | </para> |
| 303 | </refsect1> |
| 304 | <refsect1 id="Copyright"><title>Copyright</title> |
| 305 | <para> |
| 306 | Copyright <trademark class="copyright"></trademark> 2006 Khronos Group. |
| 307 | This material may be distributed subject to the terms and conditions set forth in |
| 308 | the Open Publication License, v 1.0, 8 June 1999. |
| 309 | <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>. |
| 310 | </para> |
| 311 | </refsect1> |
| 312 | </refentry> |