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<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>