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4 Reference Pages
</title><meta name=
"generator" content=
"DocBook XSL Stylesheets V1.69.1" /></head><body><div class=
"refentry" lang=
"en" xml:
lang=
"en"><a id=
"glGetActiveAttrib"></a><div class=
"titlepage"></div><div class=
"refnamediv"><h2>Name
</h2><p>glGetActiveAttrib — Returns information about an active attribute 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">glGetActiveAttrib
</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
5 queried.
</p></dd><dt><span class=
"term"><em class=
"parameter"><code>index
</code></em></span></dt><dd><p>Specifies the index of the attribute variable
6 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
7 OpenGL is allowed to write in the character buffer
8 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
9 written by OpenGL in the string indicated by
10 <em class=
"parameter"><code>name
</code></em> (excluding the null
11 terminator) if a value other than
12 <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 attribute
13 variable.
</p></dd><dt><span class=
"term"><em class=
"parameter"><code>type
</code></em></span></dt><dd><p>Returns the data type of the attribute
14 variable.
</p></dd><dt><span class=
"term"><em class=
"parameter"><code>name
</code></em></span></dt><dd><p>Returns a null terminated string containing
15 the name of the attribute 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">glGetActiveAttrib
</code> returns information
16 about an active attribute variable in the program object
17 specified by
<em class=
"parameter"><code>program
</code></em>. The number of
18 active attributes can be obtained by calling
19 <a href=
"glGetProgram.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glGetProgram
</span></span></a>
20 with the value
<code class=
"constant">GL_ACTIVE_ATTRIBUTES
</code>. A
21 value of
0 for
<em class=
"parameter"><code>index
</code></em> selects the first
22 active attribute variable. Permissible values for
23 <em class=
"parameter"><code>index
</code></em> range from
0 to the number of
24 active attribute variables minus
1.
</p><p>A vertex shader may use either built-in attribute
25 variables, user-defined attribute variables, or both. Built-in
26 attribute variables have a prefix of
"gl_" and
27 reference conventional OpenGL vertex attribtes (e.g.,
28 <em class=
"parameter"><code>gl_Vertex
</code></em>,
29 <em class=
"parameter"><code>gl_Normal
</code></em>, etc., see the OpenGL Shading
30 Language specification for a complete list.) User-defined
31 attribute variables have arbitrary names and obtain their values
32 through numbered generic vertex attributes. An attribute
33 variable (either built-in or user-defined) is considered active
34 if it is determined during the link operation that it may be
35 accessed during program execution. Therefore,
36 <em class=
"parameter"><code>program
</code></em> should have previously been the
38 <a href=
"glLinkProgram.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glLinkProgram
</span></span></a>,
39 but it is not necessary for it to have been linked
40 successfully.
</p><p>The size of the character buffer required to store the
41 longest attribute variable name in
42 <em class=
"parameter"><code>program
</code></em> can be obtained by calling
43 <a href=
"glGetProgram.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glGetProgram
</span></span></a>
45 <code class=
"constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH
</code>. This value
46 should be used to allocate a buffer of sufficient size to store
47 the returned attribute name. The size of this character buffer
48 is passed in
<em class=
"parameter"><code>bufSize
</code></em>, and a pointer to
49 this character buffer is passed in
50 <em class=
"parameter"><code>name
</code></em>.
</p><p><code class=
"function">glGetActiveAttrib
</code> returns the name of
51 the attribute variable indicated by
52 <em class=
"parameter"><code>index
</code></em>, storing it in the character buffer
53 specified by
<em class=
"parameter"><code>name
</code></em>. The string returned
54 will be null terminated. The actual number of characters written
55 into this buffer is returned in
<em class=
"parameter"><code>length
</code></em>,
56 and this count does not include the null termination character.
57 If the length of the returned string is not required, a value of
58 <code class=
"constant">NULL
</code> can be passed in the
59 <em class=
"parameter"><code>length
</code></em> argument.
</p><p>The
<em class=
"parameter"><code>type
</code></em> argument specifies a
60 pointer to a variable into which the attribute variable's data type
61 will be written. The symbolic
62 constants
<code class=
"constant">GL_FLOAT
</code>,
63 <code class=
"constant">GL_FLOAT_VEC2
</code>,
64 <code class=
"constant">GL_FLOAT_VEC3
</code>,
65 <code class=
"constant">GL_FLOAT_VEC4
</code>,
66 <code class=
"constant">GL_FLOAT_MAT2
</code>,
67 <code class=
"constant">GL_FLOAT_MAT3
</code>,
68 <code class=
"constant">GL_FLOAT_MAT4
</code>,
69 <code class=
"constant">GL_FLOAT_MAT2x3
</code>,
70 <code class=
"constant">GL_FLOAT_MAT2x4
</code>,
71 <code class=
"constant">GL_FLOAT_MAT3x2
</code>,
72 <code class=
"constant">GL_FLOAT_MAT3x4
</code>,
73 <code class=
"constant">GL_FLOAT_MAT4x2
</code>,
74 <code class=
"constant">GL_FLOAT_MAT4x3
</code>,
75 <code class=
"constant">GL_INT
</code>,
76 <code class=
"constant">GL_INT_VEC2
</code>,
77 <code class=
"constant">GL_INT_VEC3
</code>,
78 <code class=
"constant">GL_INT_VEC4
</code>,
79 <code class=
"constant">GL_UNSIGNED_INT_VEC
</code>,
80 <code class=
"constant">GL_UNSIGNED_INT_VEC2
</code>,
81 <code class=
"constant">GL_UNSIGNED_INT_VEC3
</code>,
82 <code class=
"constant">GL_UNSIGNED_INT_VEC4
</code>,
83 <code class=
"constant">DOUBLE
</code>,
84 <code class=
"constant">DOUBLE_VEC2
</code>,
85 <code class=
"constant">DOUBLE_VEC3
</code>,
86 <code class=
"constant">DOUBLE_VEC4
</code>,
87 <code class=
"constant">DOUBLE_MAT2
</code>,
88 <code class=
"constant">DOUBLE_MAT3
</code>,
89 <code class=
"constant">DOUBLE_MAT4
</code>,
90 <code class=
"constant">DOUBLE_MAT2x3
</code>,
91 <code class=
"constant">DOUBLE_MAT2x4
</code>,
92 <code class=
"constant">DOUBLE_MAT3x2
</code>,
93 <code class=
"constant">DOUBLE_MAT3x4
</code>,
94 <code class=
"constant">DOUBLE_MAT4x2
</code>, or
95 <code class=
"constant">DOUBLE_MAT4x3
</code>
97 <em class=
"parameter"><code>size
</code></em> argument will return the size of the
98 attribute, in units of the type returned in
99 <em class=
"parameter"><code>type
</code></em>.
</p><p>The list of active attribute variables may include both
100 built-in attribute variables (which begin with the prefix
101 "gl_") as well as user-defined attribute variable
102 names.
</p><p>This function will return as much information as it can
103 about the specified active attribute variable. If no information
104 is available,
<em class=
"parameter"><code>length
</code></em> will be
0, and
105 <em class=
"parameter"><code>name
</code></em> will be an empty string. This
106 situation could occur if this function is called after a link
107 operation that failed. If an error occurs, the return values
108 <em class=
"parameter"><code>length
</code></em>,
<em class=
"parameter"><code>size
</code></em>,
109 <em class=
"parameter"><code>type
</code></em>, and
<em class=
"parameter"><code>name
</code></em>
110 will be unmodified.
</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
111 <em class=
"parameter"><code>program
</code></em> is not a value generated by
112 OpenGL.
</p><p><code class=
"constant">GL_INVALID_OPERATION
</code> is generated if
113 <em class=
"parameter"><code>program
</code></em> is not a program object.
</p><p><code class=
"constant">GL_INVALID_VALUE
</code> is generated if
114 <em class=
"parameter"><code>index
</code></em> is greater than or equal to the
115 number of active attribute variables in
116 <em class=
"parameter"><code>program
</code></em>.
</p><p><code class=
"constant">GL_INVALID_VALUE
</code> is generated if
117 <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 href=
"glGet.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glGet
</span></span></a>
118 with argument
<code class=
"constant">GL_MAX_VERTEX_ATTRIBS
</code>.
</p><p><a href=
"glGetProgram.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glGetProgram
</span></span></a>
119 with argument
<code class=
"constant">GL_ACTIVE_ATTRIBUTES
</code> or
120 <code class=
"constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH
</code>.
</p><p><a 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 href=
"glBindAttribLocation.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glBindAttribLocation
</span></span></a>,
121 <a href=
"glLinkProgram.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glLinkProgram
</span></span></a>,
122 <a href=
"glVertexAttrib.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glVertexAttrib
</span></span></a>,
123 <a href=
"glVertexAttribPointer.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glVertexAttribPointer
</span></span></a></p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"Copyright"></a><h2>Copyright
</h2><p>
124 Copyright
<span class=
"trademark"></span>©
2003-
2005 3Dlabs Inc. Ltd.
125 Copyright
<span class=
"trademark"></span>©
2010 Khronos Group.
126 This material may be distributed subject to the terms and conditions set forth in
127 the Open Publication License, v
1.0,
8 June
1999.
128 <a href=
"http://opencontent.org/openpub/" target=
"_top">http://opencontent.org/openpub/
</a>.
129 </p></div></div></body></html>