<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>

<!-- Converted by db4-upgrade version 1.1 -->

<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glGetActiveUniform">
    <info>
        <copyright>
            <year>2003-2005</year>
            <holder>3Dlabs Inc. Ltd.</holder>
        </copyright>
        <copyright>
            <year>2010-2014</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glGetActiveUniform</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glGetActiveUniform</refname>
        <refpurpose>Returns information about an active uniform variable for the specified program object</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
    <funcsynopsis>
        <funcprototype>
        <funcdef>void <function>glGetActiveUniform</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLuint <parameter>index</parameter></paramdef>
        <paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
        <paramdef>GLsizei *<parameter>length</parameter></paramdef>
        <paramdef>GLint *<parameter>size</parameter></paramdef>
        <paramdef>GLenum *<parameter>type</parameter></paramdef>
        <paramdef>GLchar *<parameter>name</parameter></paramdef>
        </funcprototype>
    </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
    <variablelist>
        <varlistentry>
        <term><parameter>program</parameter></term>
        <listitem>
            <para>Specifies the program object to be
            queried.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>index</parameter></term>
        <listitem>
            <para>Specifies the index of the uniform variable to
            be queried.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>bufSize</parameter></term>
        <listitem>
            <para>Specifies the maximum number of characters
            OpenGL is allowed to write in the character buffer
            indicated by <parameter>name</parameter>.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>length</parameter></term>
        <listitem>
            <para>Returns the number of characters actually
            written by OpenGL in the string indicated by
            <parameter>name</parameter> (excluding the null
            terminator) if a value other than
            <constant>NULL</constant> is passed.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>size</parameter></term>
        <listitem>
            <para>Returns the size of the uniform
            variable.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>type</parameter></term>
        <listitem>
            <para>Returns the data type of the uniform
            variable.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>name</parameter></term>
        <listitem>
            <para>Returns a null terminated string containing
            the name of the uniform variable.</para>
        </listitem>
        </varlistentry>
    </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
    <para><function>glGetActiveUniform</function> returns
    information about an active uniform variable in the program
    object specified by <parameter>program</parameter>. The number
    of active uniform variables can be obtained by calling
    <citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
    with the value <constant>GL_ACTIVE_UNIFORMS</constant>. A value
    of zero for <parameter>index</parameter> selects the first active
    uniform variable. Permissible values for
    <parameter>index</parameter> range from zero to the number of
    active uniform variables minus one.</para>

    <para>Shaders may use either built-in uniform variables,
    user-defined uniform variables, or both. Built-in uniform
    variables have a prefix of &quot;gl_&quot; and reference
    existing OpenGL state or values derived from such state (e.g.,
    <parameter>gl_DepthRange</parameter>, see the OpenGL
    Shading Language specification for a complete list.)
    User-defined uniform variables have arbitrary names and obtain
    their values from the application through calls to
    <citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>.
    A uniform 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,
    <parameter>program</parameter> should have previously been the
    target of a call to
    <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
    but it is not necessary for it to have been linked
    successfully.</para>

    <para>The size of the character buffer required to store the
    longest uniform variable name in <parameter>program</parameter>
    can be obtained by calling
    <citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
    with the value
    <constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant>. This value
    should be used to allocate a buffer of sufficient size to store
    the returned uniform variable name. The size of this character
    buffer is passed in <parameter>bufSize</parameter>, and a
    pointer to this character buffer is passed in
    <parameter>name.</parameter></para>

    <para><function>glGetActiveUniform</function> returns the name
    of the uniform variable indicated by
    <parameter>index</parameter>, storing it in the character buffer
    specified by <parameter>name</parameter>. The string returned
    will be null terminated. The actual number of characters written
    into this buffer is returned in <parameter>length</parameter>,
    and this count does not include the null termination character.
    If the length of the returned string is not required, a value of
    <constant>NULL</constant> can be passed in the
    <parameter>length</parameter> argument.</para>

    <para>The <parameter>type</parameter>
    argument will return a pointer to the uniform variable's data
    type. The symbolic constants returned for uniform types are shown in the
    table below.
        <informaltable>
            <tgroup cols="2" align="left">
                <colspec colwidth="1.1*"/>
                <colspec colwidth="1*"/>
                <thead>
                    <row>
                        <entry>
                            <emphasis role="bold"> Returned Symbolic Contant </emphasis>
                        </entry>
                            <entry><emphasis role="bold"> Shader Uniform Type </emphasis>
                        </entry>
                    </row>
                </thead>
                <tbody>
                    <row>
                        <entry>
                            <constant>GL_FLOAT</constant>
                        </entry>
                        <entry>
                            <constant>float</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_VEC2</constant>
                        </entry>
                        <entry>
                            <constant>vec2</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_VEC3</constant>
                        </entry>
                        <entry>
                            <constant>vec3</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_VEC4</constant>
                        </entry>
                        <entry>
                            <constant>vec4</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT</constant>
                        </entry>
                        <entry>
                            <constant>int</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT_VEC2</constant>
                        </entry>
                        <entry>
                            <constant>ivec2</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT_VEC3</constant>
                        </entry>
                        <entry>
                            <constant>ivec3</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT_VEC4</constant>
                        </entry>
                        <entry>
                            <constant>ivec4</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT</constant>
                        </entry>
                        <entry>
                            <constant>unsigned int</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT_VEC2</constant>
                        </entry>
                        <entry>
                            <constant>uvec2</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT_VEC3</constant>
                        </entry>
                        <entry>
                            <constant>uvec3</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT_VEC4</constant>
                        </entry>
                        <entry>
                            <constant>uvec4</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_BOOL</constant>
                        </entry>
                        <entry>
                            <constant>bool</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_BOOL_VEC2</constant>
                        </entry>
                        <entry>
                            <constant>bvec2</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_BOOL_VEC3</constant>
                        </entry>
                        <entry>
                            <constant>bvec3</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_BOOL_VEC4</constant>
                        </entry>
                        <entry>
                            <constant>bvec4</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT2</constant>
                        </entry>
                        <entry>
                            <constant>mat2</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT3</constant>
                        </entry>
                        <entry>
                            <constant>mat3</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT4</constant>
                        </entry>
                        <entry>
                            <constant>mat4</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT2x3</constant>
                        </entry>
                        <entry>
                            <constant>mat2x3</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT2x4</constant>
                        </entry>
                        <entry>
                            <constant>mat2x4</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT3x2</constant>
                        </entry>
                        <entry>
                            <constant>mat3x2</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT3x4</constant>
                        </entry>
                        <entry>
                            <constant>mat3x4</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT4x2</constant>
                        </entry>
                        <entry>
                            <constant>mat4x2</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_FLOAT_MAT4x3</constant>
                        </entry>
                        <entry>
                            <constant>mat4x3</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_SAMPLER_2D</constant>
                        </entry>
                        <entry>
                            <constant>sampler2D</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_SAMPLER_3D</constant>
                        </entry>
                        <entry>
                            <constant>sampler3D</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_SAMPLER_CUBE</constant>
                        </entry>
                        <entry>
                            <constant>samplerCube</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_SAMPLER_2D_SHADOW</constant>
                        </entry>
                        <entry>
                            <constant>sampler2DShadow</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_SAMPLER_2D_ARRAY</constant>
                        </entry>
                        <entry>
                            <constant>sampler2DArray</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_SAMPLER_2D_ARRAY_SHADOW</constant>
                        </entry>
                        <entry>
                            <constant>sampler2DArrayShadow</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_SAMPLER_CUBE_SHADOW</constant>
                        </entry>
                        <entry>
                            <constant>samplerCubeShadow</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT_SAMPLER_2D</constant>
                        </entry>
                        <entry>
                            <constant>isampler2D</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT_SAMPLER_3D</constant>
                        </entry>
                        <entry>
                            <constant>isampler3D</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT_SAMPLER_CUBE</constant>
                        </entry>
                        <entry>
                            <constant>isamplerCube</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_INT_SAMPLER_2D_ARRAY</constant>
                        </entry>
                        <entry>
                            <constant>isampler2DArray</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT_SAMPLER_2D</constant>
                        </entry>
                        <entry>
                            <constant>usampler2D</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT_SAMPLER_3D</constant>
                        </entry>
                        <entry>
                            <constant>usampler3D</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT_SAMPLER_CUBE</constant>
                        </entry>
                        <entry>
                            <constant>usamplerCube</constant>
                        </entry>
                    </row>
                    <row>
                        <entry>
                            <constant>GL_UNSIGNED_INT_SAMPLER_2D_ARRAY</constant>
                        </entry>
                        <entry>
                            <constant>usampler2DArray</constant>
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </para>

    <para>If one or more elements of an array are active, the name
    of the array is returned in <parameter>name</parameter>, the
    type is returned in <parameter>type</parameter>, and the
    <parameter>size</parameter> parameter returns the highest array
    element index used, plus one, as determined by the compiler
    and/or linker. Only one active uniform variable will be reported
    for a uniform array. If the active uniform is an array, the uniform 
        name returned in <parameter>name</parameter> will always
        be the name of the uniform array appended with "[0]".</para>

    <para>Uniform variables that are declared as structures or
    arrays of structures will not be returned directly by this
    function. Instead, each of these uniform variables will be
    reduced to its fundamental components containing the
    &quot;.&quot; and &quot;[]&quot; operators such that each of the
    names is valid as an argument to
    <citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>.
    Each of these reduced uniform variables is counted as one active
    uniform variable and is assigned an index. A valid name cannot
    be a structure, an array of structures, or a subcomponent of a
    vector or matrix.</para>

    <para>The size of the uniform variable will be returned in
    <parameter>size</parameter>. Uniform variables other than arrays
    will have a size of 1. Structures and arrays of structures will
    be reduced as described earlier, such that each of the names
    returned will be a data type in the earlier list. If this
    reduction results in an array, the size returned will be as
    described for uniform arrays; otherwise, the size returned will
    be 1.</para>

    <para>The list of active uniform variables may include both
    built-in uniform variables (which begin with the prefix
    &quot;gl_&quot;) as well as user-defined uniform variable
    names.</para>

    <para>This function will return as much information as it can
    about the specified active uniform variable. If no information
    is available, <parameter>length</parameter> will be 0, and
    <parameter>name</parameter> 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
    <parameter>length</parameter>, <parameter>size</parameter>,
    <parameter>type</parameter>, and <parameter>name</parameter>
    will be unmodified.</para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
    <para><constant>GL_INVALID_VALUE</constant> is generated if
    <parameter>program</parameter> is not a value generated by
    OpenGL.</para>

    <para><constant>GL_INVALID_OPERATION</constant> is generated if
    <parameter>program</parameter> is not a program object.</para>

    <para><constant>GL_INVALID_VALUE</constant> is generated if
    <parameter>index</parameter> is greater than or equal to the
    number of active uniform variables in
    <parameter>program</parameter>.</para>

    <para><constant>GL_INVALID_VALUE</constant> is generated if
    <parameter>bufSize</parameter> is less than 0.</para>
    </refsect1>
    <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
    <para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
    with argument <constant>GL_MAX_VERTEX_UNIFORM_COMPONENTS</constant>,
    <constant>GL_MAX_FRAGMENT_UNIFORM_COMPONENTS</constant>, 
    <constant>GL_MAX_COMBINED_VERTEX_UNIFORM_COMPONENTS</constant>, or
    <constant>GL_MAX_COMBINED_FRAGMENT_UNIFORM_COMPONENTS</constant>.</para>

    <para><citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
    with argument <constant>GL_ACTIVE_UNIFORMS</constant> or
    <constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant>.</para>

    <para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="3" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry>glGetActiveUniform</entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
    <para><citerefentry><refentrytitle>glGetUniform</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2003-2005 3Dlabs Inc. Ltd.
            Copyright <trademark class="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.
            <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
        </para>
    </refsect1>
</refentry>
