upstream-man-pages/man2/xhtml/glGetActiveAttrib.xml

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   3 <?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>glGetActiveAttrib</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glGetActiveAttrib"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glGetActiveAttrib — Returns information about an active attribute variable for the specified program object</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glGetActiveAttrib</b>(</code></td><td>GLuint  </td><td><var class="pdparam">program</var>, </td></tr><tr><td> </td><td>GLuint  </td><td><var class="pdparam">index</var>, </td></tr><tr><td> </td><td>GLsizei  </td><td><var class="pdparam">bufSize</var>, </td></tr><tr><td> </td><td>GLsizei * </td><td><var class="pdparam">length</var>, </td></tr><tr><td> </td><td>GLint * </td><td><var class="pdparam">size</var>, </td></tr><tr><td> </td><td>GLenum * </td><td><var class="pdparam">type</var>, </td></tr><tr><td> </td><td>GLchar * </td><td><var class="pdparam">name</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>program</code></em></span></dt><dd><p>Specifies the program object to be
   4                     queried.</p></dd><dt><span class="term"><em class="parameter"><code>index</code></em></span></dt><dd><p>Specifies the index of the attribute variable
   5                     to be queried.</p></dd><dt><span class="term"><em class="parameter"><code>bufSize</code></em></span></dt><dd><p>Specifies the maximum number of characters
   6                     OpenGL is allowed to write in the character buffer
   7                     indicated by <em class="parameter"><code>name</code></em>.</p></dd><dt><span class="term"><em class="parameter"><code>length</code></em></span></dt><dd><p>Returns the number of characters actually
   8                     written by OpenGL in the string indicated by
   9                     <em class="parameter"><code>name</code></em> (excluding the null
  10                     terminator) if a value other than
  11                     <code class="constant">NULL</code> is passed.</p></dd><dt><span class="term"><em class="parameter"><code>size</code></em></span></dt><dd><p>Returns the size of the attribute
  12                     variable.</p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>Returns the data type of the attribute
  13                     variable.</p></dd><dt><span class="term"><em class="parameter"><code>name</code></em></span></dt><dd><p>Returns a null terminated string containing
  14                     the name of the attribute variable.</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p><code class="function">glGetActiveAttrib</code> returns information
  15         about an active attribute variable in the program object
  16         specified by <em class="parameter"><code>program</code></em>. The number of
  17         active attributes can be obtained by calling
  18         <a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
  19         with the value <code class="constant">GL_ACTIVE_ATTRIBUTES</code>. A
  20         value of 0 for <em class="parameter"><code>index</code></em> selects the first
  21         active attribute variable. Permissible values for
  22         <em class="parameter"><code>index</code></em> range from 0 to the number of
  23         active attribute variables minus 1.</p><p>A vertex shader may use either built-in attribute
  24         variables, user-defined attribute variables, or both. Built-in
  25         attribute variables have a prefix of "gl_" and
  26         reference conventional OpenGL vertex attribtes (e.g.,
  27         <em class="parameter"><code>gl_Vertex</code></em>,
  28         <em class="parameter"><code>gl_Normal</code></em>, etc., see the OpenGL Shading
  29         Language specification for a complete list.) User-defined
  30         attribute variables have arbitrary names and obtain their values
  31         through numbered generic vertex attributes. An attribute
  32         variable (either built-in or user-defined) is considered active
  33         if it is determined during the link operation that it may be
  34         accessed during program execution. Therefore,
  35         <em class="parameter"><code>program</code></em> should have previously been the
  36         target of a call to
  37         <a class="citerefentry" href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
  38         but it is not necessary for it to have been linked
  39         successfully.</p><p>The size of the character buffer required to store the
  40         longest attribute variable name in
  41         <em class="parameter"><code>program</code></em> can be obtained by calling
  42         <a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
  43         with the value
  44         <code class="constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</code>. This value
  45         should be used to allocate a buffer of sufficient size to store
  46         the returned attribute name. The size of this character buffer
  47         is passed in <em class="parameter"><code>bufSize</code></em>, and a pointer to
  48         this character buffer is passed in
  49         <em class="parameter"><code>name</code></em>.</p><p><code class="function">glGetActiveAttrib</code> returns the name of
  50         the attribute variable indicated by
  51         <em class="parameter"><code>index</code></em>, storing it in the character buffer
  52         specified by <em class="parameter"><code>name</code></em>. The string returned
  53         will be null terminated. The actual number of characters written
  54         into this buffer is returned in <em class="parameter"><code>length</code></em>,
  55         and this count does not include the null termination character.
  56         If the length of the returned string is not required, a value of
  57         <code class="constant">NULL</code> can be passed in the
  58         <em class="parameter"><code>length</code></em> argument.</p><p>The <em class="parameter"><code>type</code></em> argument will return a
  59         pointer to the attribute variable's data type. The symbolic
  60         constants <code class="constant">GL_FLOAT</code>,
  61         <code class="constant">GL_FLOAT_VEC2</code>,
  62         <code class="constant">GL_FLOAT_VEC3</code>,
  63         <code class="constant">GL_FLOAT_VEC4</code>,
  64         <code class="constant">GL_FLOAT_MAT2</code>,
  65         <code class="constant">GL_FLOAT_MAT3</code>,
  66         <code class="constant">GL_FLOAT_MAT4</code>,
  67         <code class="constant">GL_FLOAT_MAT2x3</code>,
  68         <code class="constant">GL_FLOAT_MAT2x4</code>,
  69         <code class="constant">GL_FLOAT_MAT3x2</code>,
  70         <code class="constant">GL_FLOAT_MAT3x4</code>,
  71         <code class="constant">GL_FLOAT_MAT4x2</code>, or
  72         <code class="constant">GL_FLOAT_MAT4x3</code> may be returned. The
  73         <em class="parameter"><code>size</code></em> argument will return the size of the
  74         attribute, in units of the type returned in
  75         <em class="parameter"><code>type</code></em>.</p><p>The list of active attribute variables may include both
  76         built-in attribute variables (which begin with the prefix
  77         "gl_") as well as user-defined attribute variable
  78         names.</p><p>This function will return as much information as it can
  79         about the specified active attribute variable. If no information
  80         is available, <em class="parameter"><code>length</code></em> will be 0, and
  81         <em class="parameter"><code>name</code></em> will be an empty string. This
  82         situation could occur if this function is called after a link
  83         operation that failed. If an error occurs, the return values
  84         <em class="parameter"><code>length</code></em>, <em class="parameter"><code>size</code></em>,
  85         <em class="parameter"><code>type</code></em>, and <em class="parameter"><code>name</code></em>
  86         will be unmodified.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p><code class="function">glGetActiveAttrib</code>
  87         is available only if the GL version is 2.0 or greater.</p><p><code class="constant">GL_FLOAT_MAT2x3</code>,
  88         <code class="constant">GL_FLOAT_MAT2x4</code>,
  89         <code class="constant">GL_FLOAT_MAT3x2</code>,
  90         <code class="constant">GL_FLOAT_MAT3x4</code>,
  91         <code class="constant">GL_FLOAT_MAT4x2</code>, and
  92         <code class="constant">GL_FLOAT_MAT4x3</code>
  93         will only be returned as a <em class="parameter"><code>type</code></em>
  94         if the GL version is 2.1 or greater.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p><code class="constant">GL_INVALID_VALUE</code> is generated if
  95         <em class="parameter"><code>program</code></em> is not a value generated by
  96         OpenGL.</p><p><code class="constant">GL_INVALID_OPERATION</code> is generated if
  97         <em class="parameter"><code>program</code></em> is not a program object.</p><p><code class="constant">GL_INVALID_VALUE</code> is generated if
  98         <em class="parameter"><code>index</code></em> is greater than or equal to the
  99         number of active attribute variables in
 100         <em class="parameter"><code>program</code></em>.</p><p><code class="constant">GL_INVALID_OPERATION</code> is generated if
 101         <code class="function">glGetActiveAttrib</code> is executed between the
 102         execution of
 103         <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>
 104         and the corresponding execution of
 105         <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.</p><p><code class="constant">GL_INVALID_VALUE</code> is generated if
 106         <em class="parameter"><code>bufSize</code></em> is less than 0.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p><a class="citerefentry" href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>
 107         with argument <code class="constant">GL_MAX_VERTEX_ATTRIBS</code>.</p><p><a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
 108         with argument <code class="constant">GL_ACTIVE_ATTRIBUTES</code> or
 109         <code class="constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</code>.</p><p><a class="citerefentry" href="glIsProgram.xml"><span class="citerefentry"><span class="refentrytitle">glIsProgram</span></span></a></p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p><a class="citerefentry" href="glBindAttribLocation.xml"><span class="citerefentry"><span class="refentrytitle">glBindAttribLocation</span></span></a>,
 110         <a class="citerefentry" href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
 111         <a class="citerefentry" href="glVertexAttrib.xml"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,
 112         <a class="citerefentry" href="glVertexAttribPointer.xml"><span class="citerefentry"><span class="refentrytitle">glVertexAttribPointer</span></span></a></p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
 113             Copyright <span class="trademark"></span>© 2003-2005 3Dlabs Inc. Ltd.
 114             This material may be distributed subject to the terms and conditions set forth in
 115             the Open Publication License, v 1.0, 8 June 1999.
 116             <a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
 117         </p></div></div></body></html>