+++ /dev/null
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
- "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
-<refentry id="glStencilFunc">
- <refmeta>
- <refmetainfo>
- <copyright>
- <year>1991-2006</year>
- <holder>Silicon Graphics, Inc.</holder>
- </copyright>
- </refmetainfo>
- <refentrytitle>glStencilFunc</refentrytitle>
- <manvolnum>3G</manvolnum>
- </refmeta>
- <refnamediv>
- <refname>glStencilFunc</refname>
- <refpurpose>set front and back function and reference value for stencil testing</refpurpose>
- </refnamediv>
- <!-- eqn: ignoring delim $$ -->
- <refsynopsisdiv><title>C Specification</title>
- <funcsynopsis>
- <funcprototype>
- <funcdef>void <function>glStencilFunc</function></funcdef>
- <paramdef>GLenum <parameter>func</parameter></paramdef>
- <paramdef>GLint <parameter>ref</parameter></paramdef>
- <paramdef>GLuint <parameter>mask</parameter></paramdef>
- </funcprototype>
- </funcsynopsis>
- </refsynopsisdiv>
- <refsect1 id="parameters"><title>Parameters</title>
- <variablelist>
- <varlistentry>
- <term><parameter>func</parameter></term>
- <listitem>
- <para>
- Specifies the test function.
- Eight symbolic constants are valid:
- <constant>GL_NEVER</constant>,
- <constant>GL_LESS</constant>,
- <constant>GL_LEQUAL</constant>,
- <constant>GL_GREATER</constant>,
- <constant>GL_GEQUAL</constant>,
- <constant>GL_EQUAL</constant>,
- <constant>GL_NOTEQUAL</constant>, and
- <constant>GL_ALWAYS</constant>. The initial value is <constant>GL_ALWAYS</constant>.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>ref</parameter></term>
- <listitem>
- <para>
- Specifies the reference value for the stencil test.
- <parameter>ref</parameter> is clamped to the range
- <inlineequation><mml:math>
- <!-- eqn: [0, 2 sup n - 1]:-->
- <mml:mfenced open="[" close="]">
- <mml:mn>0</mml:mn>
- <mml:mrow>
- <mml:msup><mml:mn>2</mml:mn>
- <mml:mi mathvariant="italic">n</mml:mi>
- </mml:msup>
- <mml:mo>-</mml:mo>
- <mml:mn>1</mml:mn>
- </mml:mrow>
- </mml:mfenced>
- </mml:math></inlineequation>,
- where
- <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
- is the number of bitplanes in the stencil buffer. The
- initial value is 0.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>mask</parameter></term>
- <listitem>
- <para>
- Specifies a mask that is ANDed with both the reference value
- and the stored stencil value when the test is done. The initial value
- is all 1's.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
- <refsect1 id="description"><title>Description</title>
- <para>
- Stenciling,
- like depth-buffering,
- enables and disables drawing on a per-pixel basis.
- Stencil planes are first drawn into using GL drawing primitives, then
- geometry and images are rendered using the stencil planes to mask out
- portions of the screen.
- Stenciling is typically used in multipass rendering algorithms
- to achieve special effects,
- such as decals,
- outlining,
- and constructive solid geometry rendering.
- </para>
- <para>
- The stencil test conditionally eliminates a pixel based on the outcome
- of a comparison between the reference value
- and the value in the stencil buffer.
- To enable and disable the test, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>
- with argument <constant>GL_STENCIL_TEST</constant>.
- To specify actions based on the outcome of the stencil test, call
- <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> or
- <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>.
- </para>
- <para>
- There can be two separate sets of <parameter>func</parameter>, <parameter>ref</parameter>, and
- <parameter>mask</parameter> parameters; one affects back-facing polygons, and the other
- affects front-facing polygons as well as other non-polygon primitives.
- <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> sets both front
- and back stencil state to the same values. Use <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>
- to set front and back stencil state to different values.
- </para>
- <para>
- <parameter>func</parameter> is a symbolic constant that determines the stencil comparison function.
- It accepts one of eight values,
- shown in the following list.
- <parameter>ref</parameter> is an integer reference value that is used in the stencil comparison.
- It is clamped to the range
- <inlineequation><mml:math>
- <!-- eqn: [0, 2 sup n - 1]:-->
- <mml:mfenced open="[" close="]">
- <mml:mn>0</mml:mn>
- <mml:mrow>
- <mml:msup><mml:mn>2</mml:mn>
- <mml:mi mathvariant="italic">n</mml:mi>
- </mml:msup>
- <mml:mo>-</mml:mo>
- <mml:mn>1</mml:mn>
- </mml:mrow>
- </mml:mfenced>
- </mml:math></inlineequation>,
- where
- <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
- is the number of bitplanes in the stencil buffer.
- <parameter>mask</parameter> is bitwise ANDed with both the reference value
- and the stored stencil value,
- with the ANDed values participating in the comparison.
- </para>
- <para>
- If <emphasis>stencil</emphasis> represents the value stored in the corresponding
- stencil buffer location,
- the following list shows the effect of each comparison function
- that can be specified by <parameter>func</parameter>.
- Only if the comparison succeeds is the pixel passed through
- to the next stage in the rasterization process
- (see <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>).
- All tests treat <emphasis>stencil</emphasis> values as unsigned integers in the range
- <inlineequation><mml:math>
- <!-- eqn: [0, 2 sup n - 1]:-->
- <mml:mfenced open="[" close="]">
- <mml:mn>0</mml:mn>
- <mml:mrow>
- <mml:msup><mml:mn>2</mml:mn>
- <mml:mi mathvariant="italic">n</mml:mi>
- </mml:msup>
- <mml:mo>-</mml:mo>
- <mml:mn>1</mml:mn>
- </mml:mrow>
- </mml:mfenced>
- </mml:math></inlineequation>,
- where
- <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
- is the number of bitplanes in the stencil buffer.
- </para>
- <para>
- The following values are accepted by <parameter>func</parameter>:
- </para>
- <variablelist>
- <varlistentry>
- <term><constant>GL_NEVER</constant></term>
- <listitem>
- <para>
- Always fails.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><constant>GL_LESS</constant></term>
- <listitem>
- <para>
- Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) < ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><constant>GL_LEQUAL</constant></term>
- <listitem>
- <para>
- Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) <= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><constant>GL_GREATER</constant></term>
- <listitem>
- <para>
- Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) > ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><constant>GL_GEQUAL</constant></term>
- <listitem>
- <para>
- Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) >= ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><constant>GL_EQUAL</constant></term>
- <listitem>
- <para>
- Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) = ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><constant>GL_NOTEQUAL</constant></term>
- <listitem>
- <para>
- Passes if ( <parameter>ref</parameter> & <parameter>mask</parameter> ) != ( <emphasis>stencil</emphasis> & <parameter>mask</parameter> ).
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><constant>GL_ALWAYS</constant></term>
- <listitem>
- <para>
- Always passes.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
- <refsect1 id="notes"><title>Notes</title>
- <para>
- Initially, the stencil test is disabled.
- If there is no stencil buffer,
- no stencil modification can occur and it is as if
- the stencil test always passes.
- </para>
- <para>
- <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> is the same as
- calling <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>
- with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>.
- </para>
- </refsect1>
- <refsect1 id="errors"><title>Errors</title>
- <para>
- <constant>GL_INVALID_ENUM</constant> is generated if <parameter>func</parameter> is not one of the eight
- accepted values.
- </para>
- <para>
- <constant>GL_INVALID_OPERATION</constant> is generated if <function>glStencilFunc</function>
- is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
- and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
- </para>
- </refsect1>
- <refsect1 id="associatedgets"><title>Associated Gets</title>
- <para>
- <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument
- <constant>GL_STENCIL_FUNC</constant>, <constant>GL_STENCIL_VALUE_MASK</constant>,
- <constant>GL_STENCIL_REF</constant>, <constant>GL_STENCIL_BACK_FUNC</constant>,
- <constant>GL_STENCIL_BACK_VALUE_MASK</constant>, <constant>GL_STENCIL_BACK_REF</constant>,
- or <constant>GL_STENCIL_BITS</constant>
- </para>
- <para>
- <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_TEST</constant>
- </para>
- </refsect1>
- <refsect1 id="seealso"><title>See Also</title>
- <para>
- <citerefentry><refentrytitle>glAlphaFunc</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>,
- <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>
- </para>
- </refsect1>
- <refsect1 id="Copyright"><title>Copyright</title>
- <para>
- Copyright <trademark class="copyright"></trademark> 1991-2006
- Silicon Graphics, Inc. This document is licensed under the SGI
- Free Software B License. For details, see
- <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
- </para>
- </refsect1>
-</refentry>
HCoop / clinton / guile-figl.git / blobdiff