| 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="glHint"> |
| 5 | <refmeta> |
| 6 | <refmetainfo> |
| 7 | <copyright> |
| 8 | <year>1991-2006</year> |
| 9 | <holder>Silicon Graphics, Inc.</holder> |
| 10 | </copyright> |
| 11 | </refmetainfo> |
| 12 | <refentrytitle>glHint</refentrytitle> |
| 13 | <manvolnum>3G</manvolnum> |
| 14 | </refmeta> |
| 15 | <refnamediv> |
| 16 | <refname>glHint</refname> |
| 17 | <refpurpose>specify implementation-specific hints</refpurpose> |
| 18 | </refnamediv> |
| 19 | <refsynopsisdiv><title>C Specification</title> |
| 20 | <funcsynopsis> |
| 21 | <funcprototype> |
| 22 | <funcdef>void <function>glHint</function></funcdef> |
| 23 | <paramdef>GLenum <parameter>target</parameter></paramdef> |
| 24 | <paramdef>GLenum <parameter>mode</parameter></paramdef> |
| 25 | </funcprototype> |
| 26 | </funcsynopsis> |
| 27 | </refsynopsisdiv> |
| 28 | <refsect1 id="parameters"><title>Parameters</title> |
| 29 | <variablelist> |
| 30 | <varlistentry> |
| 31 | <term><parameter>target</parameter></term> |
| 32 | <listitem> |
| 33 | <para> |
| 34 | Specifies a symbolic constant indicating the behavior to be controlled. |
| 35 | <constant>GL_LINE_SMOOTH_HINT</constant>, |
| 36 | <constant>GL_POLYGON_SMOOTH_HINT</constant>, |
| 37 | <constant>GL_TEXTURE_COMPRESSION_HINT</constant>, and |
| 38 | <constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant> |
| 39 | are accepted. |
| 40 | </para> |
| 41 | </listitem> |
| 42 | </varlistentry> |
| 43 | <varlistentry> |
| 44 | <term><parameter>mode</parameter></term> |
| 45 | <listitem> |
| 46 | <para> |
| 47 | Specifies a symbolic constant indicating the desired behavior. |
| 48 | <constant>GL_FASTEST</constant>, |
| 49 | <constant>GL_NICEST</constant>, and |
| 50 | <constant>GL_DONT_CARE</constant> are accepted. |
| 51 | </para> |
| 52 | </listitem> |
| 53 | </varlistentry> |
| 54 | </variablelist> |
| 55 | </refsect1> |
| 56 | <refsect1 id="description"><title>Description</title> |
| 57 | <para> |
| 58 | Certain aspects of GL behavior, |
| 59 | when there is room for interpretation, |
| 60 | can be controlled with hints. |
| 61 | A hint is specified with two arguments. |
| 62 | <parameter>target</parameter> is a symbolic |
| 63 | constant indicating the behavior to be controlled, |
| 64 | and <parameter>mode</parameter> is another symbolic constant indicating the desired |
| 65 | behavior. The initial value for each <parameter>target</parameter> is <constant>GL_DONT_CARE</constant>. |
| 66 | <parameter>mode</parameter> can be one of the following: |
| 67 | </para> |
| 68 | <variablelist> |
| 69 | <varlistentry> |
| 70 | <term><constant>GL_FASTEST</constant></term> |
| 71 | <listitem> |
| 72 | <para> |
| 73 | </para> |
| 74 | <para> |
| 75 | The most efficient option should be chosen. |
| 76 | </para> |
| 77 | </listitem> |
| 78 | </varlistentry> |
| 79 | <varlistentry> |
| 80 | <term><constant>GL_NICEST</constant></term> |
| 81 | <listitem> |
| 82 | <para> |
| 83 | </para> |
| 84 | <para> |
| 85 | The most correct, |
| 86 | or highest quality, |
| 87 | option should be chosen. |
| 88 | </para> |
| 89 | </listitem> |
| 90 | </varlistentry> |
| 91 | <varlistentry> |
| 92 | <term><constant>GL_DONT_CARE</constant></term> |
| 93 | <listitem> |
| 94 | <para> |
| 95 | </para> |
| 96 | <para> |
| 97 | No preference. |
| 98 | </para> |
| 99 | </listitem> |
| 100 | </varlistentry> |
| 101 | </variablelist> |
| 102 | <para> |
| 103 | Though the implementation aspects that can be hinted are well defined, |
| 104 | the interpretation of the hints depends on the implementation. |
| 105 | The hint aspects that can be specified with <parameter>target</parameter>, |
| 106 | along with suggested semantics, |
| 107 | are as follows: |
| 108 | </para> |
| 109 | <variablelist> |
| 110 | <varlistentry> |
| 111 | <term><constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant></term> |
| 112 | <listitem> |
| 113 | <para> |
| 114 | </para> |
| 115 | <para> |
| 116 | Indicates the accuracy of the derivative calculation for the GL shading language fragment processing built-in functions: |
| 117 | <constant>dFdx</constant>, <constant>dFdy</constant>, and <constant>fwidth</constant>. |
| 118 | </para> |
| 119 | </listitem> |
| 120 | </varlistentry> |
| 121 | <varlistentry> |
| 122 | <term><constant>GL_LINE_SMOOTH_HINT</constant></term> |
| 123 | <listitem> |
| 124 | <para> |
| 125 | </para> |
| 126 | <para> |
| 127 | Indicates the sampling quality of antialiased lines. |
| 128 | If a larger filter function is applied, hinting <constant>GL_NICEST</constant> can |
| 129 | result in more pixel fragments being generated during rasterization. |
| 130 | </para> |
| 131 | </listitem> |
| 132 | </varlistentry> |
| 133 | <varlistentry> |
| 134 | <term><constant>GL_POLYGON_SMOOTH_HINT</constant></term> |
| 135 | <listitem> |
| 136 | <para> |
| 137 | </para> |
| 138 | <para> |
| 139 | Indicates the sampling quality of antialiased polygons. |
| 140 | Hinting <constant>GL_NICEST</constant> can result in more pixel fragments being generated |
| 141 | during rasterization, |
| 142 | if a larger filter function is applied. |
| 143 | </para> |
| 144 | </listitem> |
| 145 | </varlistentry> |
| 146 | <varlistentry> |
| 147 | <term><constant>GL_TEXTURE_COMPRESSION_HINT</constant></term> |
| 148 | <listitem> |
| 149 | <para> |
| 150 | </para> |
| 151 | <para> |
| 152 | Indicates the quality and performance of the compressing texture images. |
| 153 | Hinting <constant>GL_FASTEST</constant> indicates that texture images should be compressed |
| 154 | as quickly as possible, while <constant>GL_NICEST</constant> indicates that texture images |
| 155 | should be compressed with as little image quality loss as possible. |
| 156 | <constant>GL_NICEST</constant> should be selected if the texture is to be retrieved by |
| 157 | <citerefentry><refentrytitle>glGetCompressedTexImage</refentrytitle></citerefentry> for reuse. |
| 158 | </para> |
| 159 | </listitem> |
| 160 | </varlistentry> |
| 161 | </variablelist> |
| 162 | </refsect1> |
| 163 | <refsect1 id="notes"><title>Notes</title> |
| 164 | <para> |
| 165 | The interpretation of hints depends on the implementation. |
| 166 | Some implementations ignore <function>glHint</function> settings. |
| 167 | </para> |
| 168 | </refsect1> |
| 169 | <refsect1 id="errors"><title>Errors</title> |
| 170 | <para> |
| 171 | <constant>GL_INVALID_ENUM</constant> is generated if either <parameter>target</parameter> or <parameter>mode</parameter> is not |
| 172 | an accepted value. |
| 173 | </para> |
| 174 | </refsect1> |
| 175 | <refsect1 id="Copyright"><title>Copyright</title> |
| 176 | <para> |
| 177 | Copyright <trademark class="copyright"></trademark> 1991-2006 |
| 178 | Silicon Graphics, Inc. This document is licensed under the SGI |
| 179 | Free Software B License. For details, see |
| 180 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. |
| 181 | </para> |
| 182 | </refsect1> |
| 183 | </refentry> |