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<!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="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. 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>Successfully installing an executable on a programmable
processor will cause the corresponding fixed functionality of
OpenGL to be disabled. Specifically, if an executable is
installed on the vertex processor, the OpenGL fixed
functionality will be disabled as follows.</para>
<itemizedlist>
<listitem>
<para>The modelview matrix is not applied to vertex
coordinates.</para>
</listitem>
<listitem>
<para>The projection matrix is not applied to vertex
coordinates.</para>
</listitem>
<listitem>
<para>The texture matrices are not applied to texture
coordinates.</para>
</listitem>
<listitem>
<para>Normals are not transformed to eye
coordinates.</para>
</listitem>
<listitem>
<para>Normals are not rescaled or normalized.</para>
</listitem>
<listitem>
<para>Normalization of
<constant>GL_AUTO_NORMAL</constant> evaluated normals is
not performed.</para>
</listitem>
<listitem>
<para>Texture coordinates are not generated
automatically.</para>
</listitem>
<listitem>
<para>Per-vertex lighting is not performed.</para>
</listitem>
<listitem>
<para>Color material computations are not
performed.</para>
</listitem>
<listitem>
<para>Color index lighting is not performed.</para>
</listitem>
<listitem>
<para>This list also applies when setting the current
raster position.</para>
</listitem>
</itemizedlist>
<para>The executable that is installed on the vertex processor
is expected to implement any or all of the desired functionality
from the preceding list. Similarly, if an executable is
installed on the fragment processor, the OpenGL fixed
functionality will be disabled as follows.</para>
<itemizedlist>
<listitem>
<para>Texture environment and texture functions are not
applied.</para>
</listitem>
<listitem>
<para>Texture application is not applied.</para>
</listitem>
<listitem>
<para>Color sum is not applied.</para>
</listitem>
<listitem>
<para>Fog is not applied.</para>
</listitem>
</itemizedlist>
<para>Again, the fragment shader that is installed is expected
to implement any or all of the desired functionality from the
preceding list.</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> contains shader objects
of type <constant>GL_VERTEX_SHADER</constant> but it does not
contain shader objects of type
<constant>GL_FRAGMENT_SHADER</constant>, an executable will be
installed on the vertex processor, but fixed functionality will
be used for 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>, an
executable will be installed on the fragment processor, but
fixed functionality will be used for vertex processing. If
<parameter>program</parameter> is 0, the programmable processors
will be disabled, and fixed functionality will be used for both
vertex and fragment processing.</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para><function>glUseProgram</function> is available only if the
GL version is 2.0 or greater.</para>
<para>While a program object is in use, the state that controls
the disabled fixed functionality may also be updated using the
normal OpenGL calls.</para>
<para>Like display lists 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
<function>glUseProgram</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 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>gllAttachShader</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>