upstream-doc/man2/glGetActiveAttrib.xml

   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="glGetActiveAttrib">
   5     <refmeta>
   6         <refentrytitle>glGetActiveAttrib</refentrytitle>
   7         <manvolnum>3G</manvolnum>
   8     </refmeta>
   9     <refnamediv>
  10         <refname>glGetActiveAttrib</refname>
  11         <refpurpose>Returns information about an active attribute variable for the specified program object</refpurpose>
  12     </refnamediv>
  13     <refsynopsisdiv><title>C Specification</title>
  14         <funcsynopsis>
  15             <funcprototype>
  16                 <funcdef>void <function>glGetActiveAttrib</function></funcdef>
  17                 <paramdef>GLuint <parameter>program</parameter></paramdef>
  18                 <paramdef>GLuint <parameter>index</parameter></paramdef>
  19                 <paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
  20                 <paramdef>GLsizei *<parameter>length</parameter></paramdef>
  21                 <paramdef>GLint *<parameter>size</parameter></paramdef>
  22                 <paramdef>GLenum *<parameter>type</parameter></paramdef>
  23                 <paramdef>GLchar *<parameter>name</parameter></paramdef>
  24             </funcprototype>
  25         </funcsynopsis>
  26     </refsynopsisdiv>
  27     <refsect1 id="parameters"><title>Parameters</title>
  28         <variablelist>
  29             <varlistentry>
  30                 <term><parameter>program</parameter></term>
  31                 <listitem>
  32                     <para>Specifies the program object to be
  33                     queried.</para>
  34                 </listitem>
  35             </varlistentry>
  36             <varlistentry>
  37                 <term><parameter>index</parameter></term>
  38                 <listitem>
  39                     <para>Specifies the index of the attribute variable
  40                     to be queried.</para>
  41                 </listitem>
  42             </varlistentry>
  43             <varlistentry>
  44                 <term><parameter>bufSize</parameter></term>
  45                 <listitem>
  46                     <para>Specifies the maximum number of characters
  47                     OpenGL is allowed to write in the character buffer
  48                     indicated by <parameter>name</parameter>.</para>
  49                 </listitem>
  50             </varlistentry>
  51             <varlistentry>
  52                 <term><parameter>length</parameter></term>
  53                 <listitem>
  54                     <para>Returns the number of characters actually
  55                     written by OpenGL in the string indicated by
  56                     <parameter>name</parameter> (excluding the null
  57                     terminator) if a value other than
  58                     <constant>NULL</constant> is passed.</para>
  59                 </listitem>
  60             </varlistentry>
  61             <varlistentry>
  62                 <term><parameter>size</parameter></term>
  63                 <listitem>
  64                     <para>Returns the size of the attribute
  65                     variable.</para>
  66                 </listitem>
  67             </varlistentry>
  68             <varlistentry>
  69                 <term><parameter>type</parameter></term>
  70                 <listitem>
  71                     <para>Returns the data type of the attribute
  72                     variable.</para>
  73                 </listitem>
  74             </varlistentry>
  75             <varlistentry>
  76                 <term><parameter>name</parameter></term>
  77                 <listitem>
  78                     <para>Returns a null terminated string containing
  79                     the name of the attribute variable.</para>
  80                 </listitem>
  81             </varlistentry>
  82         </variablelist>
  83     </refsect1>
  84     <refsect1 id="description"><title>Description</title>
  85         <para><function>glGetActiveAttrib</function> returns information
  86         about an active attribute variable in the program object
  87         specified by <parameter>program</parameter>. The number of
  88         active attributes can be obtained by calling
  89         <citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
  90         with the value <constant>GL_ACTIVE_ATTRIBUTES</constant>. A
  91         value of 0 for <parameter>index</parameter> selects the first
  92         active attribute variable. Permissible values for
  93         <parameter>index</parameter> range from 0 to the number of
  94         active attribute variables minus 1.</para>
  95
  96         <para>A vertex shader may use either built-in attribute
  97         variables, user-defined attribute variables, or both. Built-in
  98         attribute variables have a prefix of &quot;gl_&quot; and
  99         reference conventional OpenGL vertex attribtes (e.g.,
 100         <parameter>gl_Vertex</parameter>,
 101         <parameter>gl_Normal</parameter>, etc., see the OpenGL Shading
 102         Language specification for a complete list.) User-defined
 103         attribute variables have arbitrary names and obtain their values
 104         through numbered generic vertex attributes. An attribute
 105         variable (either built-in or user-defined) is considered active
 106         if it is determined during the link operation that it may be
 107         accessed during program execution. Therefore,
 108         <parameter>program</parameter> should have previously been the
 109         target of a call to
 110         <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
 111         but it is not necessary for it to have been linked
 112         successfully.</para>
 113
 114         <para>The size of the character buffer required to store the
 115         longest attribute variable name in
 116         <parameter>program</parameter> can be obtained by calling
 117         <citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
 118         with the value
 119         <constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>. This value
 120         should be used to allocate a buffer of sufficient size to store
 121         the returned attribute name. The size of this character buffer
 122         is passed in <parameter>bufSize</parameter>, and a pointer to
 123         this character buffer is passed in
 124         <parameter>name</parameter>.</para>
 125
 126         <para><function>glGetActiveAttrib</function> returns the name of
 127         the attribute variable indicated by
 128         <parameter>index</parameter>, storing it in the character buffer
 129         specified by <parameter>name</parameter>. The string returned
 130         will be null terminated. The actual number of characters written
 131         into this buffer is returned in <parameter>length</parameter>,
 132         and this count does not include the null termination character.
 133         If the length of the returned string is not required, a value of
 134         <constant>NULL</constant> can be passed in the
 135         <parameter>length</parameter> argument.</para>
 136
 137         <para>The <parameter>type</parameter> argument will return a
 138         pointer to the attribute variable's data type. The symbolic
 139         constants <constant>GL_FLOAT</constant>,
 140         <constant>GL_FLOAT_VEC2</constant>,
 141         <constant>GL_FLOAT_VEC3</constant>,
 142         <constant>GL_FLOAT_VEC4</constant>,
 143         <constant>GL_FLOAT_MAT2</constant>,
 144         <constant>GL_FLOAT_MAT3</constant>,
 145         <constant>GL_FLOAT_MAT4</constant>,
 146         <constant>GL_FLOAT_MAT2x3</constant>,
 147         <constant>GL_FLOAT_MAT2x4</constant>,
 148         <constant>GL_FLOAT_MAT3x2</constant>,
 149         <constant>GL_FLOAT_MAT3x4</constant>,
 150         <constant>GL_FLOAT_MAT4x2</constant>, or
 151         <constant>GL_FLOAT_MAT4x3</constant> may be returned. The
 152         <parameter>size</parameter> argument will return the size of the
 153         attribute, in units of the type returned in
 154         <parameter>type</parameter>.</para>
 155
 156         <para>The list of active attribute variables may include both
 157         built-in attribute variables (which begin with the prefix
 158         &quot;gl_&quot;) as well as user-defined attribute variable
 159         names.</para>
 160
 161         <para>This function will return as much information as it can
 162         about the specified active attribute variable. If no information
 163         is available, <parameter>length</parameter> will be 0, and
 164         <parameter>name</parameter> will be an empty string. This
 165         situation could occur if this function is called after a link
 166         operation that failed. If an error occurs, the return values
 167         <parameter>length</parameter>, <parameter>size</parameter>,
 168         <parameter>type</parameter>, and <parameter>name</parameter>
 169         will be unmodified.</para>
 170     </refsect1>
 171     <refsect1 id="notes"><title>Notes</title>
 172         <para><function>glGetActiveAttrib</function>
 173         is available only if the GL version is 2.0 or greater.</para>
 174
 175         <para><constant>GL_FLOAT_MAT2x3</constant>,
 176         <constant>GL_FLOAT_MAT2x4</constant>,
 177         <constant>GL_FLOAT_MAT3x2</constant>,
 178         <constant>GL_FLOAT_MAT3x4</constant>,
 179         <constant>GL_FLOAT_MAT4x2</constant>, and
 180         <constant>GL_FLOAT_MAT4x3</constant>
 181         will only be returned as a <parameter>type</parameter>
 182         if the GL version is 2.1 or greater.</para>
 183     </refsect1>
 184     <refsect1 id="errors"><title>Errors</title>
 185         <para><constant>GL_INVALID_VALUE</constant> is generated if
 186         <parameter>program</parameter> is not a value generated by
 187         OpenGL.</para>
 188
 189         <para><constant>GL_INVALID_OPERATION</constant> is generated if
 190         <parameter>program</parameter> is not a program object.</para>
 191
 192         <para><constant>GL_INVALID_VALUE</constant> is generated if
 193         <parameter>index</parameter> is greater than or equal to the
 194         number of active attribute variables in
 195         <parameter>program</parameter>.</para>
 196
 197         <para><constant>GL_INVALID_OPERATION</constant> is generated if
 198         <function>glGetActiveAttrib</function> is executed between the
 199         execution of
 200         <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
 201         and the corresponding execution of
 202         <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</para>
 203
 204         <para><constant>GL_INVALID_VALUE</constant> is generated if
 205         <parameter>bufSize</parameter> is less than 0.</para>
 206     </refsect1>
 207     <refsect1 id="associatedgets"><title>Associated Gets</title>
 208         <para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
 209         with argument <constant>GL_MAX_VERTEX_ATTRIBS</constant>.</para>
 210
 211         <para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
 212         with argument <constant>GL_ACTIVE_ATTRIBUTES</constant> or
 213         <constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>.</para>
 214
 215         <para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
 216     </refsect1>
 217     <refsect1 id="seealso"><title>See Also</title>
 218         <para><citerefentry><refentrytitle>glBindAttribLocation</refentrytitle></citerefentry>,
 219         <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
 220         <citerefentry><refentrytitle>glVertexAttrib</refentrytitle></citerefentry>,
 221         <citerefentry><refentrytitle>glVertexAttribPointer</refentrytitle></citerefentry></para>
 222     </refsect1>
 223     <refsect1 id="Copyright"><title>Copyright</title>
 224         <para>
 225             Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd.
 226             This material may be distributed subject to the terms and conditions set forth in
 227             the Open Publication License, v 1.0, 8 June 1999.
 228             <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
 229         </para>
 230     </refsect1>
 231 </refentry>