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247 lines
10 KiB
XML
247 lines
10 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glGetActiveUniform">
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<refmeta>
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<refentrytitle>glGetActiveUniform</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glGetActiveUniform</refname>
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<refpurpose>return information about an active uniform variable</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glGetActiveUniform</function></funcdef>
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<paramdef>GLuint <parameter>program</parameter></paramdef>
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<paramdef>GLuint <parameter>index</parameter></paramdef>
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<paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
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<paramdef>GLsizei *<parameter>length</parameter></paramdef>
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<paramdef>GLint *<parameter>size</parameter></paramdef>
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<paramdef>GLenum *<parameter>type</parameter></paramdef>
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<paramdef>GLchar *<parameter>name</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>program</parameter></term>
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<listitem>
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<para>Specifies the program object to be
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queried.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>index</parameter></term>
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<listitem>
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<para>Specifies the index of the uniform variable to
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be queried.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>bufSize</parameter></term>
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<listitem>
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<para>Specifies the maximum number of characters
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OpenGL is allowed to write in the character buffer
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indicated by <parameter>name</parameter>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>length</parameter></term>
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<listitem>
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<para>Returns the number of characters actually
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written by OpenGL in the string indicated by
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<parameter>name</parameter> (excluding the null
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terminator) if a value other than
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<constant>NULL</constant> is passed.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>size</parameter></term>
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<listitem>
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<para>Returns the size of the uniform
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variable.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>type</parameter></term>
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<listitem>
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<para>Returns the data type of the uniform
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variable.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>name</parameter></term>
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<listitem>
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<para>Returns a null terminated string containing
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the name of the uniform variable.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para><function>glGetActiveUniform</function> returns
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information about an active uniform variable in the program
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object specified by <parameter>program</parameter>. The number
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of active uniform variables can be obtained by calling
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<citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
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with the value <constant>GL_ACTIVE_UNIFORMS</constant>. A value
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of 0 for <parameter>index</parameter> selects the first active
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uniform variable. Permissible values for
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<parameter>index</parameter> range from 0 to the number of
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active uniform variables minus 1.</para>
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<para>Shaders may use either built-in uniform variables,
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user-defined uniform variables, or both. Built-in uniform
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variables have a prefix of "gl_" and reference
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existing OpenGL state or values derived from such state (e.g.,
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<parameter>gl_DepthRange</parameter>).
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User-defined uniform variables have arbitrary names and obtain
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their values from the application through calls to
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<citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>.
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A uniform variable (either built-in or user-defined) is
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considered active if it is determined during the link operation
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that it may be accessed during program execution. Therefore,
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<parameter>program</parameter> should have previously been the
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target of a call to
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<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
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but it is not necessary for it to have been linked
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successfully.</para>
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<para>The size of the character buffer required to store the
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longest uniform variable name in <parameter>program</parameter>
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can be obtained by calling
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<citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
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with the value
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<constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant>. This value
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should be used to allocate a buffer of sufficient size to store
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the returned uniform variable name. The size of this character
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buffer is passed in <parameter>bufSize</parameter>, and a
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pointer to this character buffer is passed in
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<parameter>name.</parameter></para>
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<para><function>glGetActiveUniform</function> returns the name
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of the uniform variable indicated by
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<parameter>index</parameter>, storing it in the character buffer
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specified by <parameter>name</parameter>. The string returned
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will be null terminated. The actual number of characters written
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into this buffer is returned in <parameter>length</parameter>,
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and this count does not include the null termination character.
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If the length of the returned string is not required, a value of
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<constant>NULL</constant> can be passed in the
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<parameter>length</parameter> argument.</para>
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<para>The <parameter>type</parameter>
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argument will return a pointer to the uniform variable's data
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type. The symbolic constants
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<constant>GL_FLOAT</constant>,
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<constant>GL_FLOAT_VEC2</constant>,
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<constant>GL_FLOAT_VEC3</constant>,
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<constant>GL_FLOAT_VEC4</constant>,
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<constant>GL_INT</constant>,
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<constant>GL_INT_VEC2</constant>,
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<constant>GL_INT_VEC3</constant>,
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<constant>GL_INT_VEC4</constant>,
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<constant>GL_BOOL</constant>,
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<constant>GL_BOOL_VEC2</constant>,
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<constant>GL_BOOL_VEC3</constant>,
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<constant>GL_BOOL_VEC4</constant>,
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<constant>GL_FLOAT_MAT2</constant>,
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<constant>GL_FLOAT_MAT3</constant>,
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<constant>GL_FLOAT_MAT4</constant>,
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<constant>GL_SAMPLER_2D</constant>, or
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<constant>GL_SAMPLER_CUBE</constant>
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may be returned.</para>
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<para>If one or more elements of an array are active, the name
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of the array is returned in <parameter>name</parameter>, the
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type is returned in <parameter>type</parameter>, and the
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<parameter>size</parameter> parameter returns the highest array
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element index used, plus one, as determined by the compiler
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and/or linker. Only one active uniform variable will be reported
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for a uniform array.</para>
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<para>Uniform variables that are declared as structures or
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arrays of structures will not be returned directly by this
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function. Instead, each of these uniform variables will be
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reduced to its fundamental components containing the
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"." and "[]" operators such that each of the
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names is valid as an argument to
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<citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>.
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Each of these reduced uniform variables is counted as one active
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uniform variable and is assigned an index. A valid name cannot
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be a structure, an array of structures, or a subcomponent of a
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vector or matrix.</para>
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<para>The size of the uniform variable will be returned in
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<parameter>size</parameter>. Uniform variables other than arrays
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will have a size of 1. Structures and arrays of structures will
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be reduced as described earlier, such that each of the names
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returned will be a data type in the earlier list. If this
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reduction results in an array, the size returned will be as
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described for uniform arrays; otherwise, the size returned will
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be 1.</para>
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<para>The list of active uniform variables may include both
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built-in uniform variables (which begin with the prefix
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"gl_") as well as user-defined uniform variable
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names.</para>
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<para>This function will return as much information as it can
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about the specified active uniform variable. If no information
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is available, <parameter>length</parameter> will be 0, and
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<parameter>name</parameter> will be an empty string. This
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situation could occur if this function is called after a link
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operation that failed. If an error occurs, the return values
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<parameter>length</parameter>, <parameter>size</parameter>,
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<parameter>type</parameter>, and <parameter>name</parameter>
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will be unmodified.</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>program</parameter> is not a value generated by
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OpenGL.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if
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<parameter>program</parameter> is not a program object.</para>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>index</parameter> is greater than or equal to the
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number of active uniform variables in
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<parameter>program</parameter>.</para>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>bufSize</parameter> is less than 0.</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with argument <constant>GL_MAX_VERTEX_UNIFORM_VECTORS
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</constant> or
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<constant>GL_MAX_FRAGMENT_UNIFORM_VECTORS</constant>.</para>
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<para><citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
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with argument <constant>GL_ACTIVE_UNIFORMS</constant> or
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<constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant>.</para>
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<para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para><citerefentry><refentrytitle>glGetActiveAttrib</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glGetUniform</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry></para>
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</refsect1>
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<refsect1 id="copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd.
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This material may be distributed subject to the terms and conditions set forth in
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the Open Publication License, v 1.0, 8 June 1999.
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<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
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</para>
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</refsect1>
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</refentry>
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