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<?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" /><link rel="stylesheet" type="text/css" href="opengl-man.css" /><title>glGetActiveUniformBlock - OpenGL 4 Reference Pages</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glGetActiveUniformBlock"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glGetActiveUniformBlock — query information about an active uniform block</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">glGetActiveUniformBlockiv</b>(</code></td><td>GLuint  </td><td><var class="pdparam">program</var>, </td></tr><tr><td> </td><td>GLuint  </td><td><var class="pdparam">uniformBlockIndex</var>, </td></tr><tr><td> </td><td>GLenum  </td><td><var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>GLint * </td><td><var class="pdparam">params</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 name of a program containing the uniform block.
                </p></dd><dt><span class="term"><em class="parameter"><code>uniformBlockIndex</code></em></span></dt><dd><p>
                    Specifies the index of the uniform block within <em class="parameter"><code>program</code></em>.
                </p></dd><dt><span class="term"><em class="parameter"><code>pname</code></em></span></dt><dd><p>
                    Specifies the name of the parameter to query.
                </p></dd><dt><span class="term"><em class="parameter"><code>params</code></em></span></dt><dd><p>
                    Specifies the address of a variable to receive the result of the query.
                </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            <code class="function">glGetActiveUniformBlockiv</code> retrieves information about an active uniform block within <em class="parameter"><code>program</code></em>.
        </p><p>
            <em class="parameter"><code>program</code></em> must be the name of a program object for which the command
            <a href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a> must have been called in the past, although it is not required that
            <a href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a> must have succeeded. The link could have failed because the number
            of active uniforms exceeded the limit.
        </p><p>
            <em class="parameter"><code>uniformBlockIndex</code></em> is an active uniform block index of <em class="parameter"><code>program</code></em>, and must be less than the value
            of <code class="constant">GL_ACTIVE_UNIFORM_BLOCKS</code>.
        </p><p>
            Upon success, the uniform block parameter(s) specified by <em class="parameter"><code>pname</code></em> are returned in <em class="parameter"><code>params</code></em>. If an error
            occurs, nothing will be written to <em class="parameter"><code>params</code></em>.
        </p><p>
            If <em class="parameter"><code>pname</code></em> is <code class="constant">GL_UNIFORM_BLOCK_BINDING</code>, then the index of the uniform buffer binding point
            last selected by the uniform block specified by <em class="parameter"><code>uniformBlockIndex</code></em> for <em class="parameter"><code>program</code></em> is returned. If
            no uniform block has been previously specified, zero is returned.
        </p><p>
            If <em class="parameter"><code>pname</code></em> is <code class="constant">GL_UNIFORM_BLOCK_DATA_SIZE</code>, then the implementation-dependent minimum total buffer
            object size, in basic machine units, required to hold all active uniforms in the uniform block identified by <em class="parameter"><code>uniformBlockIndex</code></em>
            is returned. It is neither guaranteed nor expected that a given implementation will arrange uniform values as tightly packed in a buffer
            object. The exception to this is the <span class="emphasis"><em>std140 uniform block layout</em></span>, which guarantees specific packing behavior and does not
            require the application to query for offsets and strides. In this case the minimum size may still be queried, even though it is determined in
            advance based only on the uniform block declaration.
        </p><p>
            If <em class="parameter"><code>pname</code></em> is <code class="constant">GL_UNIFORM_BLOCK_NAME_LENGTH</code>, then the total length (including the nul terminator) of
            the name of the uniform block identified by <em class="parameter"><code>uniformBlockIndex</code></em> is returned.
        </p><p>
            If <em class="parameter"><code>pname</code></em> is <code class="constant">GL_UNIFORM_BLOCK_ACTIVE_UNIFORMS</code>, then the number of active uniforms in the uniform
            block identified by <em class="parameter"><code>uniformBlockIndex</code></em> is returned.
        </p><p>
            If <em class="parameter"><code>pname</code></em> is <code class="constant">GL_UNIFORM_BLOCK_ACTIVE_UNIFORM_INDICES</code>, then a list of the active uniform indices
            for the uniform block identified by <em class="parameter"><code>uniformBlockIndex</code></em> is returned. The number of elements that will be written to
            <em class="parameter"><code>params</code></em> is the value of <code class="constant">GL_UNIFORM_BLOCK_ACTIVE_UNIFORMS</code> for <em class="parameter"><code>uniformBlockIndex</code></em>.
        </p><p>
            If <em class="parameter"><code>pname</code></em> is <code class="constant">GL_UNIFORM_BLOCK_REFERENCED_BY_VERTEX_SHADER</code>, <code class="constant">GL_UNIFORM_BLOCK_REFERENCED_BY_TESS_CONTROL_SHADER</code>,
            <code class="constant">GL_UNIFORM_BLOCK_REFERENCED_BY_TESS_EVALUATION_SHADER</code>, <code class="constant">GL_UNIFORM_BLOCK_REFERENCED_BY_GEOMETRY_SHADER</code>,
            <code class="constant">GL_UNIFORM_BLOCK_REFERENCED_BY_FRAGMENT_SHADER</code>, or <code class="constant">GL_UNIFORM_BLOCK_REFERENCED_BY_COMPUTE_SHADER</code>
            then a boolean value indicating whether the uniform block identified by
            <em class="parameter"><code>uniformBlockIndex</code></em> is referenced by the vertex, tessellation control, tessellation evaluation, geometry, fragment or compute
            programming stages of program, respectively, is returned.
        </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 <em class="parameter"><code>uniformBlockIndex</code></em> is greater than or equal to the value
            of <code class="constant">GL_ACTIVE_UNIFORM_BLOCKS</code> or is not the index of an active uniform block in <em class="parameter"><code>program</code></em>.
        </p><p>
            <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>pname</code></em> is not one of the accepted tokens.
        </p><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>program</code></em> is not the name of a program object for which
            <a href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a> has been called in the past.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
            <code class="function">glGetActiveUniformBlockiv</code> is available only if the GL version is 3.1 or greater.
        </p><p>
            <code class="constant">GL_UNIFORM_BLOCK_REFERENCED_BY_COMPUTE_SHADER</code> is accepted only if the GL version is 4.3
            or greater.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a href="glGetActiveUniformBlockName.xml"><span class="citerefentry"><span class="refentrytitle">glGetActiveUniformBlockName</span></span></a>,
            <a href="glGetUniformBlockIndex.xml"><span class="citerefentry"><span class="refentrytitle">glGetUniformBlockIndex</span></span></a>,
            <a href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
            Copyright <span class="trademark"></span>© 2010-2013 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 href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
        </p></div></div></body></html>
