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<refentry id="glUseProgram">
    <refmeta>
	<refentrytitle>glUseProgram</refentrytitle>
	<manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
	<refname>glUseProgram</refname>
	<refpurpose>Installs a program object as part of current rendering state</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
	<funcsynopsis>
	    <funcprototype>
		<funcdef>void <function>glUseProgram</function></funcdef>
		<paramdef>GLuint <parameter>program</parameter></paramdef>
	    </funcprototype>
	</funcsynopsis>
    </refsynopsisdiv>
    <refsect1 id="parameters"><title>Parameters</title>
	<variablelist>
	    <varlistentry>
		<term><parameter>program</parameter></term>
		<listitem>
		    <para>Specifies the handle of the program object
		    whose executables are to be used as part of current
		    rendering state.</para>
		</listitem>
	    </varlistentry>
	</variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
	<para><function>glUseProgram</function> installs the program
	object specified by <parameter>program</parameter> as part of
	current rendering state. One or more executables are created in
	a program object by successfully attaching shader objects to it
	with
	<citerefentry><refentrytitle>glAttachShader</refentrytitle></citerefentry>,
	successfully compiling the shader objects with
	<citerefentry><refentrytitle>glCompileShader</refentrytitle></citerefentry>,
	and successfully linking the program object with
	<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>.
	</para>

	<para>A program object will contain an executable that will run
	on the vertex processor if it contains one or more shader
	objects of type <constant>GL_VERTEX_SHADER</constant> that have
	been successfully compiled and linked. A program object will contain an
	executable that will run on the geometry processor if it contains one or
	more shader objects of type <constant>GL_GEOMETRY_SHADER</constant> that
	have been successfully compiled and linked.
	Similarly, a program object will contain an executable that will run on the
	fragment processor if it contains one or more shader objects of type
	<constant>GL_FRAGMENT_SHADER</constant> that have been
	successfully compiled and linked.</para>

	<para>While a program object is in use, applications are free to
	modify attached shader objects, compile attached shader objects,
	attach additional shader objects, and detach or delete shader
	objects. None of these operations will affect the executables
	that are part of the current state. However, relinking the
	program object that is currently in use will install the program
	object as part of the current rendering state if the link
	operation was successful (see
	<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>
	). If the program object currently in use is relinked
	unsuccessfully, its link status will be set to
	<constant>GL_FALSE</constant>, but the executables and
	associated state will remain part of the current state until a
	subsequent call to <function>glUseProgram</function> removes it
	from use. After it is removed from use, it cannot be made part
	of current state until it has been successfully relinked.</para>

	<para>If <parameter>program</parameter> is zero, then the current rendering
	state refers to an <emphasis>invalid</emphasis> program object and the
	results of shader execution are undefined. However, this is not an error.</para>
	
	<para>If <parameter>program</parameter> does not
	contain shader objects of type <constant>GL_FRAGMENT_SHADER</constant>, an
	executable will be installed on the vertex, and possibly geometry processors,
	but the results of fragment shader execution will be undefined.</para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
	<para>Like buffer and texture objects, the name space for
	program objects may be shared across a set of contexts, as long
	as the server sides of the contexts share the same address
	space. If the name space is shared across contexts, any attached
	objects and the data associated with those attached objects are
	shared as well.</para>

	<para>Applications are responsible for providing the
	synchronization across API calls when objects are accessed from
	different execution threads.</para>

    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
	<para><constant>GL_INVALID_VALUE</constant> is generated if
	<parameter>program</parameter> is neither 0 nor 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_OPERATION</constant> is generated if
	<parameter>program</parameter> could not be made part of current
	state.</para>
	
	<para><constant>GL_INVALID_OPERATION</constant> is generated if
	transform feedback mode is active.</para>

    </refsect1>
    <refsect1 id="associatedgets"><title>Associated Gets</title>
	<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
	with the argument <constant>GL_CURRENT_PROGRAM</constant></para>

	<para><citerefentry><refentrytitle>glGetActiveAttrib</refentrytitle></citerefentry>
	with a valid program object and the index of an active attribute
	variable</para>

	<para><citerefentry><refentrytitle>glGetActiveUniform</refentrytitle></citerefentry>
	with a valid program object and the index of an active uniform
	variable</para>

	<para><citerefentry><refentrytitle>glGetAttachedShaders</refentrytitle></citerefentry>
	with a valid program object</para>

	<para><citerefentry><refentrytitle>glGetAttribLocation</refentrytitle></citerefentry>
	with a valid program object and the name of an attribute
	variable</para>

	<para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
	with a valid program object and the parameter to be queried</para>

	<para><citerefentry><refentrytitle>glGetProgramInfoLog</refentrytitle></citerefentry>
	with a valid program object</para>

	<para><citerefentry><refentrytitle>glGetUniform</refentrytitle></citerefentry>
	with a valid program object and the location of a uniform
	variable</para>

	<para><citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>
	with a valid program object and the name of a uniform
	variable</para>

	<para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
	<para><citerefentry><refentrytitle>glAttachShader</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glBindAttribLocation</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glCompileShader</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glCreateProgram</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glDeleteProgram</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glDetachShader</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glValidateProgram</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glVertexAttrib</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd. 
            This material may be distributed subject to the terms and conditions set forth in 
            the Open Publication License, v 1.0, 8 June 1999.
            <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
        </para>
    </refsect1>
</refentry>
