<?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="glHint"> <refentryinfo> <copyright> <year>1991-2006</year> <holder>Silicon Graphics, Inc.</holder> </copyright> </refentryinfo> <refmeta> <refentrytitle>glHint</refentrytitle> <manvolnum>3G</manvolnum> </refmeta> <refnamediv> <refname>glHint</refname> <refpurpose>specify implementation-specific hints</refpurpose> </refnamediv> <refsynopsisdiv><title>C Specification</title> <funcsynopsis> <funcprototype> <funcdef>void <function>glHint</function></funcdef> <paramdef>GLenum <parameter>target</parameter></paramdef> <paramdef>GLenum <parameter>mode</parameter></paramdef> </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1 id="parameters"><title>Parameters</title> <variablelist> <varlistentry> <term><parameter>target</parameter></term> <listitem> <para> Specifies a symbolic constant indicating the behavior to be controlled. <constant>GL_LINE_SMOOTH_HINT</constant>, <constant>GL_POLYGON_SMOOTH_HINT</constant>, <constant>GL_TEXTURE_COMPRESSION_HINT</constant>, and <constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant> are accepted. </para> </listitem> </varlistentry> <varlistentry> <term><parameter>mode</parameter></term> <listitem> <para> Specifies a symbolic constant indicating the desired behavior. <constant>GL_FASTEST</constant>, <constant>GL_NICEST</constant>, and <constant>GL_DONT_CARE</constant> are accepted. </para> </listitem> </varlistentry> </variablelist> </refsect1> <refsect1 id="description"><title>Description</title> <para> Certain aspects of GL behavior, when there is room for interpretation, can be controlled with hints. A hint is specified with two arguments. <parameter>target</parameter> is a symbolic constant indicating the behavior to be controlled, and <parameter>mode</parameter> is another symbolic constant indicating the desired behavior. The initial value for each <parameter>target</parameter> is <constant>GL_DONT_CARE</constant>. <parameter>mode</parameter> can be one of the following: </para> <variablelist> <varlistentry> <term><constant>GL_FASTEST</constant></term> <listitem> <para> </para> <para> The most efficient option should be chosen. </para> </listitem> </varlistentry> <varlistentry> <term><constant>GL_NICEST</constant></term> <listitem> <para> </para> <para> The most correct, or highest quality, option should be chosen. </para> </listitem> </varlistentry> <varlistentry> <term><constant>GL_DONT_CARE</constant></term> <listitem> <para> </para> <para> No preference. </para> </listitem> </varlistentry> </variablelist> <para> Though the implementation aspects that can be hinted are well defined, the interpretation of the hints depends on the implementation. The hint aspects that can be specified with <parameter>target</parameter>, along with suggested semantics, are as follows: </para> <variablelist> <varlistentry> <term><constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant></term> <listitem> <para> </para> <para> Indicates the accuracy of the derivative calculation for the GL shading language fragment processing built-in functions: <constant>dFdx</constant>, <constant>dFdy</constant>, and <constant>fwidth</constant>. </para> </listitem> </varlistentry> <varlistentry> <term><constant>GL_LINE_SMOOTH_HINT</constant></term> <listitem> <para> </para> <para> Indicates the sampling quality of antialiased lines. If a larger filter function is applied, hinting <constant>GL_NICEST</constant> can result in more pixel fragments being generated during rasterization. </para> </listitem> </varlistentry> <varlistentry> <term><constant>GL_POLYGON_SMOOTH_HINT</constant></term> <listitem> <para> </para> <para> Indicates the sampling quality of antialiased polygons. Hinting <constant>GL_NICEST</constant> can result in more pixel fragments being generated during rasterization, if a larger filter function is applied. </para> </listitem> </varlistentry> <varlistentry> <term><constant>GL_TEXTURE_COMPRESSION_HINT</constant></term> <listitem> <para> </para> <para> Indicates the quality and performance of the compressing texture images. Hinting <constant>GL_FASTEST</constant> indicates that texture images should be compressed as quickly as possible, while <constant>GL_NICEST</constant> indicates that texture images should be compressed with as little image quality loss as possible. <constant>GL_NICEST</constant> should be selected if the texture is to be retrieved by <citerefentry><refentrytitle>glGetCompressedTexImage</refentrytitle></citerefentry> for reuse. </para> </listitem> </varlistentry> </variablelist> </refsect1> <refsect1 id="notes"><title>Notes</title> <para> The interpretation of hints depends on the implementation. Some implementations ignore <function>glHint</function> settings. </para> </refsect1> <refsect1 id="errors"><title>Errors</title> <para> <constant>GL_INVALID_ENUM</constant> is generated if either <parameter>target</parameter> or <parameter>mode</parameter> is not an accepted value. </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>