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<?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="glGetUniform">
<refmeta>
<refentrytitle>glGetUniform</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refdescriptor>glGetUniform</refdescriptor>
<refname>glGetUniformfv</refname>
<refname>glGetUniformiv</refname>
<refpurpose>Returns the value of a uniform variable</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glGetUniformfv</function></funcdef>
<paramdef>GLuint <parameter>program</parameter></paramdef>
<paramdef>GLint <parameter>location</parameter></paramdef>
<paramdef>GLfloat *<parameter>params</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>glGetUniformiv</function></funcdef>
<paramdef>GLuint <parameter>program</parameter></paramdef>
<paramdef>GLint <parameter>location</parameter></paramdef>
<paramdef>GLint *<parameter>params</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 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>location</parameter></term>
<listitem>
<para>Specifies the location of the uniform variable
to be queried.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>params</parameter></term>
<listitem>
<para>Returns the value of the specified uniform
variable.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para><function>glGetUniform</function> returns in
<parameter>params</parameter> the value(s) of the specified
uniform variable. The type of the uniform variable specified by
<parameter>location</parameter> determines the number of values
returned. If the uniform variable is defined in the shader as a
boolean, int, or float, a single value will be returned. If it
is defined as a vec2, ivec2, or bvec2, two values will be
returned. If it is defined as a vec3, ivec3, or bvec3, three
values will be returned, and so on. To query values stored in
uniform variables declared as arrays, call
<function>glGetUniform</function> for each element of the array.
To query values stored in uniform variables declared as
structures, call <function>glGetUniform</function> for each
field in the structure. The values for uniform variables
declared as a matrix will be returned in column major
order.</para>
<para>The locations assigned to uniform variables are not known
until the program object is linked. After linking has occurred,
the command
<citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>
can be used to obtain the location of a uniform variable. This
location value can then be passed to
<function>glGetUniform</function> in order to query the current
value of the uniform variable. After a program object has been
linked successfully, the index values for uniform variables
remain fixed until the next link command occurs. The uniform
variable values can only be queried after a link if the link was
successful.</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para><function>glGetUniform</function> is available only if the
GL version is 2.0 or greater.</para>
<para>If an error is generated, no change is made to the
contents of <parameter>params</parameter>.</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
<parameter>program</parameter> has not been successfully
linked.</para>
<para><constant>GL_INVALID_OPERATION</constant> is generated if
<parameter>location</parameter> does not correspond to a valid
uniform variable location for the specified program object.</para>
<para><constant>GL_INVALID_OPERATION</constant> is generated if
<function>glGetUniform</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>glGetActiveUniform</refentrytitle></citerefentry>
with arguments <parameter>program</parameter> and the index of an active
uniform variable</para>
<para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
with arguments <parameter>program</parameter> and
<constant>GL_ACTIVE_UNIFORMS</constant> or
<constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant></para>
<para><citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>
with arguments <parameter>program</parameter> 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>glCreateProgram</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glUniform</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>