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255 lines
11 KiB
XML
255 lines
11 KiB
XML
<?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="glHint">
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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>glHint</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glHint</refname>
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<refpurpose>specify implementation-specific hints</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>glHint</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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<paramdef>GLenum <parameter>mode</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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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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Specifies a symbolic constant indicating the behavior to be controlled.
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<constant>GL_FOG_HINT</constant>,
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<constant>GL_GENERATE_MIPMAP_HINT</constant>,
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<constant>GL_LINE_SMOOTH_HINT</constant>,
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<constant>GL_PERSPECTIVE_CORRECTION_HINT</constant>,
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<constant>GL_POINT_SMOOTH_HINT</constant>,
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<constant>GL_POLYGON_SMOOTH_HINT</constant>,
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<constant>GL_TEXTURE_COMPRESSION_HINT</constant>, and
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<constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant>
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are accepted.
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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>mode</parameter></term>
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<listitem>
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<para>
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Specifies a symbolic constant indicating the desired behavior.
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<constant>GL_FASTEST</constant>,
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<constant>GL_NICEST</constant>, and
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<constant>GL_DONT_CARE</constant> are accepted.
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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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Certain aspects of GL behavior,
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when there is room for interpretation,
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can be controlled with hints.
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A hint is specified with two arguments.
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<parameter>target</parameter> is a symbolic
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constant indicating the behavior to be controlled,
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and <parameter>mode</parameter> is another symbolic constant indicating the desired
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behavior. The initial value for each <parameter>target</parameter> is <constant>GL_DONT_CARE</constant>.
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<parameter>mode</parameter> can be one of the following:
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</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_FASTEST</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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The most efficient option should be chosen.
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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><constant>GL_NICEST</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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The most correct,
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or highest quality,
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option should be chosen.
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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><constant>GL_DONT_CARE</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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No preference.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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Though the implementation aspects that can be hinted are well defined,
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the interpretation of the hints depends on the implementation.
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The hint aspects that can be specified with <parameter>target</parameter>,
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along with suggested semantics,
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are as follows:
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</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_FOG_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the accuracy of fog calculation.
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If per-pixel fog calculation is not efficiently supported
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by the GL implementation,
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hinting <constant>GL_DONT_CARE</constant> or <constant>GL_FASTEST</constant> can result in per-vertex
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calculation of fog effects.
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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><constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the accuracy of the derivative calculation for the GL shading language fragment processing built-in functions:
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<constant>dFdx</constant>, <constant>dFdy</constant>, and <constant>fwidth</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><constant>GL_GENERATE_MIPMAP_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the quality of filtering when generating mipmap images.
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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><constant>GL_LINE_SMOOTH_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the sampling quality of antialiased lines.
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If a larger filter function is applied, hinting <constant>GL_NICEST</constant> can
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result in more pixel fragments being generated during rasterization.
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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><constant>GL_PERSPECTIVE_CORRECTION_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the quality of color, texture coordinate, and fog coordinate
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interpolation. If perspective-corrected parameter interpolation is not
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efficiently supported by the GL implementation, hinting <constant>GL_DONT_CARE</constant>
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or <constant>GL_FASTEST</constant> can result in simple linear interpolation of colors
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and/or texture coordinates.
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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><constant>GL_POINT_SMOOTH_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the sampling quality of antialiased points.
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If a larger filter function is applied, hinting <constant>GL_NICEST</constant> can
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result in more pixel fragments being generated during rasterization.
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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><constant>GL_POLYGON_SMOOTH_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the sampling quality of antialiased polygons.
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Hinting <constant>GL_NICEST</constant> can result in more pixel fragments being generated
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during rasterization,
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if a larger filter function is applied.
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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><constant>GL_TEXTURE_COMPRESSION_HINT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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Indicates the quality and performance of the compressing texture images.
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Hinting <constant>GL_FASTEST</constant> indicates that texture images should be compressed
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as quickly as possible, while <constant>GL_NICEST</constant> indicates that texture images
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should be compressed with as little image quality loss as possible.
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<constant>GL_NICEST</constant> should be selected if the texture is to be retrieved by
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<citerefentry><refentrytitle>glGetCompressedTexImage</refentrytitle></citerefentry> for reuse.
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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="notes"><title>Notes</title>
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<para>
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The interpretation of hints depends on the implementation.
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Some implementations ignore <function>glHint</function> settings.
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</para>
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<para>
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<constant>GL_TEXTURE_COMPRESSION_HINT</constant> is available only if the GL version is 1.3
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or greater.
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</para>
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<para>
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<constant>GL_GENERATE_MIPMAP_HINT</constant> is available only if the GL version is 1.4
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or greater.
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</para>
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<para>
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<constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant> is available only if the GL version is 2.0
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or greater.
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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 either <parameter>target</parameter> or <parameter>mode</parameter> is not
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an accepted value.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glHint</function>
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is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
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and the corresponding execution of <citerefentry><refentrytitle>glEnd</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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