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-<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>glGetActiveUniform</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glGetActiveUniform"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glGetActiveUniform — Returns information about an active uniform variable for the specified program object</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glGetActiveUniform</b>(</code></td><td>GLuint </td><td><var class="pdparam">program</var>, </td></tr><tr><td> </td><td>GLuint </td><td><var class="pdparam">index</var>, </td></tr><tr><td> </td><td>GLsizei </td><td><var class="pdparam">bufSize</var>, </td></tr><tr><td> </td><td>GLsizei * </td><td><var class="pdparam">length</var>, </td></tr><tr><td> </td><td>GLint * </td><td><var class="pdparam">size</var>, </td></tr><tr><td> </td><td>GLenum * </td><td><var class="pdparam">type</var>, </td></tr><tr><td> </td><td>GLchar * </td><td><var class="pdparam">name</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>program</code></em></span></dt><dd><p>Specifies the program object to be
- queried.</p></dd><dt><span class="term"><em class="parameter"><code>index</code></em></span></dt><dd><p>Specifies the index of the uniform variable to
- be queried.</p></dd><dt><span class="term"><em class="parameter"><code>bufSize</code></em></span></dt><dd><p>Specifies the maximum number of characters
- OpenGL is allowed to write in the character buffer
- indicated by <em class="parameter"><code>name</code></em>.</p></dd><dt><span class="term"><em class="parameter"><code>length</code></em></span></dt><dd><p>Returns the number of characters actually
- written by OpenGL in the string indicated by
- <em class="parameter"><code>name</code></em> (excluding the null
- terminator) if a value other than
- <code class="constant">NULL</code> is passed.</p></dd><dt><span class="term"><em class="parameter"><code>size</code></em></span></dt><dd><p>Returns the size of the uniform
- variable.</p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>Returns the data type of the uniform
- variable.</p></dd><dt><span class="term"><em class="parameter"><code>name</code></em></span></dt><dd><p>Returns a null terminated string containing
- the name of the uniform variable.</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p><code class="function">glGetActiveUniform</code> returns
- information about an active uniform variable in the program
- object specified by <em class="parameter"><code>program</code></em>. The number
- of active uniform variables can be obtained by calling
- <a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
- with the value <code class="constant">GL_ACTIVE_UNIFORMS</code>. A value
- of 0 for <em class="parameter"><code>index</code></em> selects the first active
- uniform variable. Permissible values for
- <em class="parameter"><code>index</code></em> range from 0 to the number of
- active uniform variables minus 1.</p><p>Shaders may use either built-in uniform variables,
- user-defined uniform variables, or both. Built-in uniform
- variables have a prefix of "gl_" and reference
- existing OpenGL state or values derived from such state (e.g.,
- <em class="parameter"><code>gl_Fog</code></em>,
- <em class="parameter"><code>gl_ModelViewMatrix</code></em>, etc., see the OpenGL
- Shading Language specification for a complete list.)
- User-defined uniform variables have arbitrary names and obtain
- their values from the application through calls to
- <a class="citerefentry" href="glUniform.xml"><span class="citerefentry"><span class="refentrytitle">glUniform</span></span></a>.
- A uniform variable (either built-in or user-defined) is
- considered active if it is determined during the link operation
- that it may be accessed during program execution. Therefore,
- <em class="parameter"><code>program</code></em> should have previously been the
- target of a call to
- <a class="citerefentry" href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
- but it is not necessary for it to have been linked
- successfully.</p><p>The size of the character buffer required to store the
- longest uniform variable name in <em class="parameter"><code>program</code></em>
- can be obtained by calling
- <a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
- with the value
- <code class="constant">GL_ACTIVE_UNIFORM_MAX_LENGTH</code>. This value
- should be used to allocate a buffer of sufficient size to store
- the returned uniform variable name. The size of this character
- buffer is passed in <em class="parameter"><code>bufSize</code></em>, and a
- pointer to this character buffer is passed in
- <em class="parameter"><code>name.</code></em></p><p><code class="function">glGetActiveUniform</code> returns the name
- of the uniform variable indicated by
- <em class="parameter"><code>index</code></em>, storing it in the character buffer
- specified by <em class="parameter"><code>name</code></em>. The string returned
- will be null terminated. The actual number of characters written
- into this buffer is returned in <em class="parameter"><code>length</code></em>,
- and this count does not include the null termination character.
- If the length of the returned string is not required, a value of
- <code class="constant">NULL</code> can be passed in the
- <em class="parameter"><code>length</code></em> argument.</p><p>The <em class="parameter"><code>type</code></em>
- argument will return a pointer to the uniform variable's data
- type. The symbolic constants
- <code class="constant">GL_FLOAT</code>,
- <code class="constant">GL_FLOAT_VEC2</code>,
- <code class="constant">GL_FLOAT_VEC3</code>,
- <code class="constant">GL_FLOAT_VEC4</code>,
- <code class="constant">GL_INT</code>,
- <code class="constant">GL_INT_VEC2</code>,
- <code class="constant">GL_INT_VEC3</code>,
- <code class="constant">GL_INT_VEC4</code>,
- <code class="constant">GL_BOOL</code>,
- <code class="constant">GL_BOOL_VEC2</code>,
- <code class="constant">GL_BOOL_VEC3</code>,
- <code class="constant">GL_BOOL_VEC4</code>,
- <code class="constant">GL_FLOAT_MAT2</code>,
- <code class="constant">GL_FLOAT_MAT3</code>,
- <code class="constant">GL_FLOAT_MAT4</code>,
- <code class="constant">GL_FLOAT_MAT2x3</code>,
- <code class="constant">GL_FLOAT_MAT2x4</code>,
- <code class="constant">GL_FLOAT_MAT3x2</code>,
- <code class="constant">GL_FLOAT_MAT3x4</code>,
- <code class="constant">GL_FLOAT_MAT4x2</code>,
- <code class="constant">GL_FLOAT_MAT4x3</code>,
- <code class="constant">GL_SAMPLER_1D</code>,
- <code class="constant">GL_SAMPLER_2D</code>,
- <code class="constant">GL_SAMPLER_3D</code>,
- <code class="constant">GL_SAMPLER_CUBE</code>,
- <code class="constant">GL_SAMPLER_1D_SHADOW</code>, or
- <code class="constant">GL_SAMPLER_2D_SHADOW</code>
- may be returned.</p><p>If one or more elements of an array are active, the name
- of the array is returned in <em class="parameter"><code>name</code></em>, the
- type is returned in <em class="parameter"><code>type</code></em>, and the
- <em class="parameter"><code>size</code></em> parameter returns the highest array
- element index used, plus one, as determined by the compiler
- and/or linker. Only one active uniform variable will be reported
- for a uniform array.</p><p>Uniform variables that are declared as structures or
- arrays of structures will not be returned directly by this
- function. Instead, each of these uniform variables will be
- reduced to its fundamental components containing the
- "." and "[]" operators such that each of the
- names is valid as an argument to
- <a class="citerefentry" href="glGetUniformLocation.xml"><span class="citerefentry"><span class="refentrytitle">glGetUniformLocation</span></span></a>.
- Each of these reduced uniform variables is counted as one active
- uniform variable and is assigned an index. A valid name cannot
- be a structure, an array of structures, or a subcomponent of a
- vector or matrix.</p><p>The size of the uniform variable will be returned in
- <em class="parameter"><code>size</code></em>. Uniform variables other than arrays
- will have a size of 1. Structures and arrays of structures will
- be reduced as described earlier, such that each of the names
- returned will be a data type in the earlier list. If this
- reduction results in an array, the size returned will be as
- described for uniform arrays; otherwise, the size returned will
- be 1.</p><p>The list of active uniform variables may include both
- built-in uniform variables (which begin with the prefix
- "gl_") as well as user-defined uniform variable
- names.</p><p>This function will return as much information as it can
- about the specified active uniform variable. If no information
- is available, <em class="parameter"><code>length</code></em> will be 0, and
- <em class="parameter"><code>name</code></em> will be an empty string. This
- situation could occur if this function is called after a link
- operation that failed. If an error occurs, the return values
- <em class="parameter"><code>length</code></em>, <em class="parameter"><code>size</code></em>,
- <em class="parameter"><code>type</code></em>, and <em class="parameter"><code>name</code></em>
- will be unmodified.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p><code class="function">glGetActiveUniform</code> is available only
- if the GL version is 2.0 or greater.</p><p><code class="constant">GL_FLOAT_MAT2x3</code>,
- <code class="constant">GL_FLOAT_MAT2x4</code>,
- <code class="constant">GL_FLOAT_MAT3x2</code>,
- <code class="constant">GL_FLOAT_MAT3x4</code>,
- <code class="constant">GL_FLOAT_MAT4x2</code>, and
- <code class="constant">GL_FLOAT_MAT4x3</code>
- will only be returned as a <em class="parameter"><code>type</code></em>
- if the GL version is 2.1 or greater.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p><code class="constant">GL_INVALID_VALUE</code> is generated if
- <em class="parameter"><code>program</code></em> is not a value generated by
- OpenGL.</p><p><code class="constant">GL_INVALID_OPERATION</code> is generated if
- <em class="parameter"><code>program</code></em> is not a program object.</p><p><code class="constant">GL_INVALID_VALUE</code> is generated if
- <em class="parameter"><code>index</code></em> is greater than or equal to the
- number of active uniform variables in
- <em class="parameter"><code>program</code></em>.</p><p><code class="constant">GL_INVALID_OPERATION</code> is generated if
- <code class="function">glGetActiveUniform</code> is executed between the
- execution of
- <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>
- and the corresponding execution of
- <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.</p><p><code class="constant">GL_INVALID_VALUE</code> is generated if
- <em class="parameter"><code>bufSize</code></em> is less than 0.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p><a class="citerefentry" href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>
- with argument <code class="constant">GL_MAX_VERTEX_UNIFORM_COMPONENTS
- </code> or
- <code class="constant">GL_MAX_FRAGMENT_UNIFORM_COMPONENTS</code>.</p><p><a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
- with argument <code class="constant">GL_ACTIVE_UNIFORMS</code> or
- <code class="constant">GL_ACTIVE_UNIFORM_MAX_LENGTH</code>.</p><p><a class="citerefentry" href="glIsProgram.xml"><span class="citerefentry"><span class="refentrytitle">glIsProgram</span></span></a></p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p><a class="citerefentry" href="glGetUniform.xml"><span class="citerefentry"><span class="refentrytitle">glGetUniform</span></span></a>,
- <a class="citerefentry" href="glGetUniformLocation.xml"><span class="citerefentry"><span class="refentrytitle">glGetUniformLocation</span></span></a>,
- <a class="citerefentry" href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
- <a class="citerefentry" href="glUniform.xml"><span class="citerefentry"><span class="refentrytitle">glUniform</span></span></a>,
- <a class="citerefentry" href="glUseProgram.xml"><span class="citerefentry"><span class="refentrytitle">glUseProgram</span></span></a></p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
- Copyright <span class="trademark"></span>© 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.
- <a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
- </p></div></div></body></html>
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