<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
	      "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="glLinkProgram">
    <refmeta>
	<refentrytitle>glLinkProgram</refentrytitle>
	<manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
	<refname>glLinkProgram</refname>
	<refpurpose>Links a program object</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
	<funcsynopsis>
	    <funcprototype>
		<funcdef>void <function>glLinkProgram</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 to be linked.</para>

		</listitem>
	    </varlistentry>
	</variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
	<para><function>glLinkProgram</function> links the program
	object specified by <parameter>program</parameter>. If any
	shader objects of type <constant>GL_VERTEX_SHADER</constant> are
	attached to <parameter>program</parameter>, they will be used to
	create an executable that will run on the programmable vertex
	processor. If any shader objects of type
	<constant>GL_FRAGMENT_SHADER</constant> are attached to
	<parameter>program</parameter>, they will be used to create an
	executable that will run on the programmable fragment
	processor.</para>

	<para>The status of the link operation will be stored as part of
	the program object's state. This value will be set to
	<constant>GL_TRUE</constant> if the program object was linked
	without errors and is ready for use, and
	<constant>GL_FALSE</constant> otherwise. It can be queried by
	calling
	<citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
	with arguments <parameter>program</parameter> and
	<constant>GL_LINK_STATUS</constant>.</para>

	<para>As a result of a successful link operation, all active
	user-defined uniform variables belonging to
	<parameter>program</parameter> will be initialized to 0, and
	each of the program object's active uniform variables will be
	assigned a location that can be queried by calling
	<citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>.
	Also, any active user-defined attribute variables that have not
	been bound to a generic vertex attribute index will be bound to
	one at this time.</para>

	<para>Linking of a program object can fail for a number of
	reasons as specified in the <emphasis>OpenGL Shading Language
	Specification</emphasis>. The following lists some of the
	conditions that will cause a link error.</para>

	<itemizedlist>
	    <listitem>
		<para>The number of active attribute variables supported
		by the implementation has been exceeded.</para>
	    </listitem>
	    <listitem>
		<para>The storage limit for uniform variables has been
		exceeded.</para>
	    </listitem>
	    <listitem>
		<para>The number of active uniform variables supported
		by the implementation has been exceeded.</para>
	    </listitem>
	    <listitem>
		<para>The <function>main</function> function is missing
		for the vertex shader or the fragment shader.</para>
	    </listitem>
	    <listitem>
		<para>A varying variable actually used in the fragment
		shader is not declared in the same way (or is not
		declared at all) in the vertex shader.</para>
	    </listitem>
	    <listitem>
		<para>A reference to a function or variable name is
		unresolved.</para>
	    </listitem>
	    <listitem>
		<para>A shared global is declared with two different
		types or two different initial values.</para>
	    </listitem>
	    <listitem>
		<para>One or more of the attached shader objects has not
		been successfully compiled.</para>
	    </listitem>
	    <listitem>
		<para>Binding a generic attribute matrix caused some
		rows of the matrix to fall outside the allowed maximum
		of <constant>GL_MAX_VERTEX_ATTRIBS</constant>.</para>
	    </listitem>
	    <listitem>
		<para>Not enough contiguous vertex attribute slots could
		be found to bind attribute matrices.</para>
	    </listitem>
	</itemizedlist>

	<para>When a program object has been successfully linked, the
	program object can be made part of current state by calling
	<citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry>.
	Whether or not the link operation was successful, the program
	object's information log will be overwritten. The information
	log can be retrieved by calling
	<citerefentry><refentrytitle>glGetProgramInfoLog</refentrytitle></citerefentry>.</para>

	<para><function>glLinkProgram</function> will also install the
	generated executables as part of the current rendering state if
	the link operation was successful and the specified program
	object is already currently in use as a result of a previous
	call to
	<citerefentry><refentrytitle>glUseProgram</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> contains shader objects
	of type <constant>GL_VERTEX_SHADER</constant> but does not
	contain shader objects of type
	<constant>GL_FRAGMENT_SHADER</constant>, the vertex shader will
	be linked against the implicit interface for fixed functionality
	fragment processing. Similarly, if
	<parameter>program</parameter> contains shader objects of type
	<constant>GL_FRAGMENT_SHADER</constant> but it does not contain
	shader objects of type <constant>GL_VERTEX_SHADER</constant>,
	the fragment shader will be linked against the implicit
	interface for fixed functionality vertex processing.</para>

	<para>The program object's information log is updated and the
	program is generated at the time of the link operation. After
	the link operation, applications are free to modify attached
	shader objects, compile attached shader objects, detach shader
	objects, delete shader objects, and attach additional shader
	objects. None of these operations affects the information log or
	the program that is part of the program object.</para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
	<para><function>glLinkProgram</function>
	is available only if the GL version is 2.0 or greater.</para>
	<para>If the link operation is unsuccessful, any information about a previous link operation on <parameter>program</parameter>
	is lost (i.e., a failed link does not restore the old state of <parameter>program</parameter>
	). Certain information can still be retrieved from <parameter>program</parameter>
	even after an unsuccessful link operation. See for instance <citerefentry><refentrytitle>glGetActiveAttrib</refentrytitle></citerefentry>
	and <citerefentry><refentrytitle>glGetActiveUniform</refentrytitle></citerefentry>.</para>
    </refsect1>
    <refsect1 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_OPERATION</constant>
	is generated if <function>glLinkProgram</function>
	is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
	and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</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 argument <parameter>program</parameter>
	and the index of an active attribute variable</para>
	<para><citerefentry><refentrytitle>glGetActiveUniform</refentrytitle></citerefentry>
	with argument <parameter>program</parameter>
	and the index of an active uniform variable<parameter></parameter></para>
	<para><citerefentry><refentrytitle>glGetAttachedShaders</refentrytitle></citerefentry>
	with argument <parameter>program</parameter></para>
	<para><citerefentry><refentrytitle>glGetAttribLocation</refentrytitle></citerefentry>
	with argument <parameter>program</parameter>
	and an attribute variable name</para>
	<para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
	with arguments <parameter>program</parameter>
	and <constant>GL_LINK_STATUS</constant></para>
	<para><citerefentry><refentrytitle>glGetProgramInfoLog</refentrytitle></citerefentry>
	with argument <parameter>program</parameter></para>
	<para><citerefentry><refentrytitle>glGetUniform</refentrytitle></citerefentry>
	with argument <parameter>program</parameter>
	and a uniform variable location</para>
	<para><citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>
	with argument <parameter>program</parameter>
	and a uniform variable name</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>glUniform</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glValidateProgram</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>
