<?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>return 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>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> </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>glGetProgramiv</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>