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206 lines
9.8 KiB
XML
206 lines
9.8 KiB
XML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glHistogram">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glHistogram</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glHistogram</refname>
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<refpurpose>define histogram table</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glHistogram</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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<paramdef>GLsizei <parameter>width</parameter></paramdef>
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<paramdef>GLenum <parameter>internalformat</parameter></paramdef>
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<paramdef>GLboolean <parameter>sink</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>target</parameter></term>
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<listitem>
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<para>
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The histogram whose parameters are to be set.
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Must be one of
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<constant>GL_HISTOGRAM</constant> or
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<constant>GL_PROXY_HISTOGRAM</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>width</parameter></term>
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<listitem>
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<para>
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The number of entries in the histogram table. Must be a power of 2.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>internalformat</parameter></term>
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<listitem>
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<para>
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The format of entries in the histogram table.
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Must be one of
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<constant>GL_ALPHA</constant>,
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<constant>GL_ALPHA4</constant>,
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<constant>GL_ALPHA8</constant>,
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<constant>GL_ALPHA12</constant>,
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<constant>GL_ALPHA16</constant>,
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<constant>GL_LUMINANCE</constant>,
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<constant>GL_LUMINANCE4</constant>,
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<constant>GL_LUMINANCE8</constant>,
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<constant>GL_LUMINANCE12</constant>,
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<constant>GL_LUMINANCE16</constant>,
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<constant>GL_LUMINANCE_ALPHA</constant>,
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<constant>GL_LUMINANCE4_ALPHA4</constant>,
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<constant>GL_LUMINANCE6_ALPHA2</constant>,
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<constant>GL_LUMINANCE8_ALPHA8</constant>,
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<constant>GL_LUMINANCE12_ALPHA4</constant>,
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<constant>GL_LUMINANCE12_ALPHA12</constant>,
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<constant>GL_LUMINANCE16_ALPHA16</constant>,
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<constant>GL_R3_G3_B2</constant>,
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<constant>GL_RGB</constant>,
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<constant>GL_RGB4</constant>,
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<constant>GL_RGB5</constant>,
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<constant>GL_RGB8</constant>,
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<constant>GL_RGB10</constant>,
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<constant>GL_RGB12</constant>,
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<constant>GL_RGB16</constant>,
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<constant>GL_RGBA</constant>,
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<constant>GL_RGBA2</constant>,
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<constant>GL_RGBA4</constant>,
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<constant>GL_RGB5_A1</constant>,
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<constant>GL_RGBA8</constant>,
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<constant>GL_RGB10_A2</constant>,
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<constant>GL_RGBA12</constant>, or
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<constant>GL_RGBA16</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>sink</parameter></term>
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<listitem>
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<para>
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If <constant>GL_TRUE</constant>, pixels will be consumed by the histogramming
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process and no drawing or texture loading will take place.
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If <constant>GL_FALSE</constant>, pixels will proceed to the minmax process after
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histogramming.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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When <constant>GL_HISTOGRAM</constant> is enabled, RGBA color components are converted to
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histogram table indices by clamping to the range [0,1], multiplying by
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the width of the histogram table, and rounding to the nearest integer.
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The table entries selected by the RGBA indices are then incremented.
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(If the internal format of the histogram table includes luminance, then
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the index derived from the R color component determines the luminance
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table entry to be incremented.) If a histogram table entry is incremented
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beyond its maximum value, then its value becomes undefined. (This is
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not an error.)
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</para>
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<para>
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Histogramming is performed only for RGBA pixels (though these may
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be specified originally as color indices and converted to RGBA by
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index table lookup).
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Histogramming is enabled with <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and disabled with <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>.
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</para>
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<para>
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When <parameter>target</parameter> is <constant>GL_HISTOGRAM</constant>, <function>glHistogram</function> redefines the current
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histogram table to have <parameter>width</parameter> entries of the format specified by
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<parameter>internalformat</parameter>.
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The entries are indexed 0 through
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<inlineequation><mml:math>
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<!-- eqn: width - 1:-->
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<mml:mrow>
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<mml:mi mathvariant="italic">width</mml:mi>
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<mml:mo>-</mml:mo>
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<mml:mn>1</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>,
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and
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all entries are initialized to zero.
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The values in the previous histogram table, if any, are lost.
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If <parameter>sink</parameter> is <constant>GL_TRUE</constant>, then pixels are discarded after histogramming;
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no further processing of the pixels takes place, and no drawing,
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texture loading, or pixel readback will result.
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</para>
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<para>
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When <parameter>target</parameter> is <constant>GL_PROXY_HISTOGRAM</constant>, <function>glHistogram</function> computes all
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state information as if the histogram table were to be redefined,
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but does not actually define the new table.
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If the requested histogram table is too large to be supported, then the
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state information will be set to zero.
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This provides a way to determine if a histogram table with the given
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parameters can be supported.
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</para>
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<para>
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</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>
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<function>glHistogram</function> is present only if <code>ARB_imaging</code> is returned when <citerefentry><refentrytitle>glGetString</refentrytitle></citerefentry>
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is called with an argument of <constant>GL_EXTENSIONS</constant>.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter> is not one of the allowable
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values.
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</para>
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<para>
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<constant>GL_INVALID_VALUE</constant> is generated if <parameter>width</parameter> is less than zero or is
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not a power of 2.
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</para>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>internalformat</parameter> is not one of the
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allowable values.
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</para>
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<para>
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<constant>GL_TABLE_TOO_LARGE</constant> is generated if <parameter>target</parameter> is <constant>GL_HISTOGRAM</constant>
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and the histogram table specified is too large for the implementation.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glHistogram</function> is executed
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between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> and the corresponding
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execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
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</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para>
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<citerefentry><refentrytitle>glGetHistogramParameter</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glGetHistogram</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glResetHistogram</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 1991-2006
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Silicon Graphics, Inc. This document is licensed under the SGI
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Free Software B License. For details, see
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<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
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</para>
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</refsect1>
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</refentry>
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