glGetActiveAttrib.xhtml

    <div class="refentry" id="glGetActiveAttrib">
      <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 style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
            <tr>
              <td>
                <code class="funcdef">void <strong class="fsfunc">glGetActiveAttrib</strong>(</code>
              </td>
              <td>GLuint <var class="pdparam">program</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>GLuint <var class="pdparam">index</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>GLsizei <var class="pdparam">bufSize</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>GLsizei *<var class="pdparam">length</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>GLint *<var class="pdparam">size</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>GLenum *<var class="pdparam">type</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>GLchar *<var class="pdparam">name</var><code>)</code>;</td>
            </tr>
          </table>
          <div class="funcprototype-spacer"> </div>
        </div>
      </div>
      <div class="refsect1" id="parameters">
        <h2>Parameters</h2>
        <div class="variablelist">
          <dl class="variablelist">
            <dt>
              <span class="term">
                <em class="parameter">
                  <code>program</code>
                </em>
              </span>
            </dt>
            <dd>
              <p>Specifies the program object to be
            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
            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
            OpenGL is allowed to write in the character buffer
            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
            written by OpenGL in the string indicated by
            <em class="parameter"><code>name</code></em> (excluding the null
            terminator) if a value other than
            <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
            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
            variable.</p>
            </dd>
            <dt>
              <span class="term">
                <em class="parameter">
                  <code>name</code>
                </em>
              </span>
            </dt>
            <dd>
              <p>Returns a null terminated string containing
            the name of the attribute variable.</p>
            </dd>
          </dl>
        </div>
      </div>
      <div class="refsect1" id="description">
        <h2>Description</h2>
        <p><code class="function">glGetActiveAttrib</code> returns information
    about an active attribute variable in the program object
    specified by <em class="parameter"><code>program</code></em>. The number of
    active attributes can be obtained by calling
    <a class="citerefentry" href="glGetProgram"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
    with the value <code class="constant">GL_ACTIVE_ATTRIBUTES</code>. A
    value of 0 for <em class="parameter"><code>index</code></em> selects the first
    active attribute variable. Permissible values for
    <em class="parameter"><code>index</code></em> range from zero to the number of
    active attribute variables minus one.</p>
        <p>A vertex shader may use either built-in attribute
    variables, user-defined attribute variables, or both. Built-in
    attribute variables have a prefix of "gl_" and
    reference conventional OpenGL vertex attribtes (e.g.,
    <em class="parameter"><code>gl_Vertex</code></em>,
    <em class="parameter"><code>gl_Normal</code></em>, etc., see the OpenGL Shading
    Language specification for a complete list.) User-defined
    attribute variables have arbitrary names and obtain their values
    through numbered generic vertex attributes. An attribute
    variable (either built-in or user-defined) is considered active
    if it is determined during the link operation that it may be
    accessed during program execution. Therefore,
    <em class="parameter"><code>program</code></em> should have previously been the
    target of a call to
    <a class="citerefentry" href="glLinkProgram"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
    but it is not necessary for it to have been linked
    successfully.</p>
        <p>The size of the character buffer required to store the
    longest attribute variable name in
    <em class="parameter"><code>program</code></em> can be obtained by calling
    <a class="citerefentry" href="glGetProgram"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
    with the value
    <code class="constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</code>. This value
    should be used to allocate a buffer of sufficient size to store
    the returned attribute name. The size of this character buffer
    is passed in <em class="parameter"><code>bufSize</code></em>, and a pointer to
    this character buffer is passed in
    <em class="parameter"><code>name</code></em>.</p>
        <p><code class="function">glGetActiveAttrib</code> returns the name of
    the attribute variable indicated by
    <em class="parameter"><code>index</code></em>, storing it in the character buffer
    specified by <em class="parameter"><code>name</code></em>. The string returned
    will be null terminated. The actual number of characters written
    into this buffer is returned in <em class="parameter"><code>length</code></em>,
    and this count does not include the null termination character.
    If the length of the returned string is not required, a value of
    <code class="constant">NULL</code> can be passed in the
    <em class="parameter"><code>length</code></em> argument.</p>
        <p>The <em class="parameter"><code>type</code></em> argument specifies a
    pointer to a variable into which the attribute variable's data type
    will be written. The symbolic
    constants <code class="constant">GL_FLOAT</code>,
    <code class="constant">GL_FLOAT_VEC2</code>,
    <code class="constant">GL_FLOAT_VEC3</code>,
    <code class="constant">GL_FLOAT_VEC4</code>,
    <code class="constant">GL_FLOAT_MAT2</code>,
    <code class="constant">GL_FLOAT_MAT3</code>,
    <code class="constant">GL_FLOAT_MAT4</code>,
    <code class="constant">GL_FLOAT_MAT2x3</code>,
    <code class="constant">GL_FLOAT_MAT2x4</code>,
    <code class="constant">GL_FLOAT_MAT3x2</code>,
    <code class="constant">GL_FLOAT_MAT3x4</code>,
    <code class="constant">GL_FLOAT_MAT4x2</code>,
    <code class="constant">GL_FLOAT_MAT4x3</code>,
    <code class="constant">GL_INT</code>,
    <code class="constant">GL_INT_VEC2</code>,
    <code class="constant">GL_INT_VEC3</code>,
    <code class="constant">GL_INT_VEC4</code>,
    <code class="constant">GL_UNSIGNED_INT</code>,
    <code class="constant">GL_UNSIGNED_INT_VEC2</code>,
    <code class="constant">GL_UNSIGNED_INT_VEC3</code>,
    <code class="constant">GL_UNSIGNED_INT_VEC4</code>,
    <code class="constant">GL_DOUBLE</code>,
    <code class="constant">GL_DOUBLE_VEC2</code>,
    <code class="constant">GL_DOUBLE_VEC3</code>,
    <code class="constant">GL_DOUBLE_VEC4</code>,
    <code class="constant">GL_DOUBLE_MAT2</code>,
    <code class="constant">GL_DOUBLE_MAT3</code>,
    <code class="constant">GL_DOUBLE_MAT4</code>,
    <code class="constant">GL_DOUBLE_MAT2x3</code>,
    <code class="constant">GL_DOUBLE_MAT2x4</code>,
    <code class="constant">GL_DOUBLE_MAT3x2</code>,
    <code class="constant">GL_DOUBLE_MAT3x4</code>,
    <code class="constant">GL_DOUBLE_MAT4x2</code>, or
    <code class="constant">GL_DOUBLE_MAT4x3</code>
     may be returned. The
    <em class="parameter"><code>size</code></em> argument will return the size of the
    attribute, in units of the type returned in
    <em class="parameter"><code>type</code></em>.</p>
        <p>The list of active attribute variables may include both
    built-in attribute variables (which begin with the prefix
    "gl_") as well as user-defined attribute variable
    names.</p>
        <p>This function will return as much information as it can
    about the specified active attribute variable. If no information
    is available, <em class="parameter"><code>length</code></em> will be 0, and
    <em class="parameter"><code>name</code></em> will be an empty string. This
    situation could occur if this function is called after a link
    operation that failed. If an error occurs, the return values
    <em class="parameter"><code>length</code></em>, <em class="parameter"><code>size</code></em>,
    <em class="parameter"><code>type</code></em>, and <em class="parameter"><code>name</code></em>
    will be unmodified.</p>
      </div>
      <div class="refsect1" id="errors">
        <h2>Errors</h2>
        <p><code class="constant">GL_INVALID_VALUE</code> is generated if
    <em class="parameter"><code>program</code></em> is not a value generated by
    OpenGL.</p>
        <p><code class="constant">GL_INVALID_OPERATION</code> is generated if
    <em class="parameter"><code>program</code></em> is not a program object.</p>
        <p><code class="constant">GL_INVALID_VALUE</code> is generated if
    <em class="parameter"><code>index</code></em> is greater than or equal to the
    number of active attribute variables in
    <em class="parameter"><code>program</code></em>.</p>
        <p><code class="constant">GL_INVALID_VALUE</code> is generated if
    <em class="parameter"><code>bufSize</code></em> is less than 0.</p>
      </div>
      <div class="refsect1" id="associatedgets">
        <h2>Associated Gets</h2>
        <p><a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>
    with argument <code class="constant">GL_MAX_VERTEX_ATTRIBS</code>.</p>
        <p><a class="citerefentry" href="glGetProgram"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
    with argument <code class="constant">GL_ACTIVE_ATTRIBUTES</code> or
    <code class="constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</code>.</p>
        <p>
          <a class="citerefentry" href="glIsProgram">
            <span class="citerefentry">
              <span class="refentrytitle">glIsProgram</span>
            </span>
          </a>
        </p>
      </div>
      {$pipelinestall}{$examples}
      <div class="refsect1" id="versions">
        <h2>Version Support</h2>
        <div class="informaltable">
          <table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">
            <colgroup>
              <col style="text-align: left; "/>
              <col style="text-align: center; " class="firstvers"/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; "/>
              <col style="text-align: center; " class="lastvers"/>
            </colgroup>
            <thead>
              <tr>
                <th style="text-align: left; border-right: 2px solid ; ">

            </th>
                <th style="text-align: center; border-bottom: 2px solid ; " colspan="12">
                <span class="bold"><strong>OpenGL Version</strong></span>
            </th>
              </tr>
              <tr>
                <th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>Function / Feature Name</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>2.0</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>2.1</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>3.0</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>3.1</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>3.2</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>3.3</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>4.0</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>4.1</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>4.2</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>4.3</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>4.4</strong></span>
            </th>
                <th style="text-align: center; border-bottom: 2px solid ; ">
                <span class="bold"><strong>4.5</strong></span>
            </th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td style="text-align: left; border-right: 2px solid ; ">
                  <code class="function">glGetActiveAttrib</code>
                </td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; ">✔</td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1" id="seealso">
        <h2>See Also</h2>
        <p><a class="citerefentry" href="glBindAttribLocation"><span class="citerefentry"><span class="refentrytitle">glBindAttribLocation</span></span></a>,
    <a class="citerefentry" href="glLinkProgram"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
    <a class="citerefentry" href="glVertexAttrib"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,
    <a class="citerefentry" href="glVertexAttribPointer"><span class="citerefentry"><span class="refentrytitle">glVertexAttribPointer</span></span></a></p>
      </div>
      <div class="refsect1" id="Copyright">
        <h2>Copyright</h2>
        <p>
            Copyright © 2003-2005 3Dlabs Inc. Ltd.
            Copyright © 2010-2014 Khronos Group.
            This material may be distributed subject to the terms and conditions set forth in
            the Open Publication License, v 1.0, 8 June 1999.
            <a class="link" href="https://opencontent.org/openpub/" target="_top">https://opencontent.org/openpub/</a>.
        </p>
      </div>
    </div>