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1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd"> | |
4 | <refentry id="glGetActiveUniform"> | |
5 | <refmeta> | |
6 | <refentrytitle>glGetActiveUniform</refentrytitle> | |
7 | <manvolnum>3G</manvolnum> | |
8 | </refmeta> | |
9 | <refnamediv> | |
10 | <refname>glGetActiveUniform</refname> | |
11 | <refpurpose>Returns information about an active uniform variable for the specified program object</refpurpose> | |
12 | </refnamediv> | |
13 | <refsynopsisdiv><title>C Specification</title> | |
14 | <funcsynopsis> | |
15 | <funcprototype> | |
16 | <funcdef>void <function>glGetActiveUniform</function></funcdef> | |
17 | <paramdef>GLuint <parameter>program</parameter></paramdef> | |
18 | <paramdef>GLuint <parameter>index</parameter></paramdef> | |
19 | <paramdef>GLsizei <parameter>bufSize</parameter></paramdef> | |
20 | <paramdef>GLsizei *<parameter>length</parameter></paramdef> | |
21 | <paramdef>GLint *<parameter>size</parameter></paramdef> | |
22 | <paramdef>GLenum *<parameter>type</parameter></paramdef> | |
23 | <paramdef>GLchar *<parameter>name</parameter></paramdef> | |
24 | </funcprototype> | |
25 | </funcsynopsis> | |
26 | </refsynopsisdiv> | |
27 | <refsect1 id="parameters"><title>Parameters</title> | |
28 | <variablelist> | |
29 | <varlistentry> | |
30 | <term><parameter>program</parameter></term> | |
31 | <listitem> | |
32 | <para>Specifies the program object to be | |
33 | queried.</para> | |
34 | </listitem> | |
35 | </varlistentry> | |
36 | <varlistentry> | |
37 | <term><parameter>index</parameter></term> | |
38 | <listitem> | |
39 | <para>Specifies the index of the uniform variable to | |
40 | be queried.</para> | |
41 | </listitem> | |
42 | </varlistentry> | |
43 | <varlistentry> | |
44 | <term><parameter>bufSize</parameter></term> | |
45 | <listitem> | |
46 | <para>Specifies the maximum number of characters | |
47 | OpenGL is allowed to write in the character buffer | |
48 | indicated by <parameter>name</parameter>.</para> | |
49 | </listitem> | |
50 | </varlistentry> | |
51 | <varlistentry> | |
52 | <term><parameter>length</parameter></term> | |
53 | <listitem> | |
54 | <para>Returns the number of characters actually | |
55 | written by OpenGL in the string indicated by | |
56 | <parameter>name</parameter> (excluding the null | |
57 | terminator) if a value other than | |
58 | <constant>NULL</constant> is passed.</para> | |
59 | </listitem> | |
60 | </varlistentry> | |
61 | <varlistentry> | |
62 | <term><parameter>size</parameter></term> | |
63 | <listitem> | |
64 | <para>Returns the size of the uniform | |
65 | variable.</para> | |
66 | </listitem> | |
67 | </varlistentry> | |
68 | <varlistentry> | |
69 | <term><parameter>type</parameter></term> | |
70 | <listitem> | |
71 | <para>Returns the data type of the uniform | |
72 | variable.</para> | |
73 | </listitem> | |
74 | </varlistentry> | |
75 | <varlistentry> | |
76 | <term><parameter>name</parameter></term> | |
77 | <listitem> | |
78 | <para>Returns a null terminated string containing | |
79 | the name of the uniform variable.</para> | |
80 | </listitem> | |
81 | </varlistentry> | |
82 | </variablelist> | |
83 | </refsect1> | |
84 | <refsect1 id="description"><title>Description</title> | |
85 | <para><function>glGetActiveUniform</function> returns | |
86 | information about an active uniform variable in the program | |
87 | object specified by <parameter>program</parameter>. The number | |
88 | of active uniform variables can be obtained by calling | |
89 | <citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry> | |
90 | with the value <constant>GL_ACTIVE_UNIFORMS</constant>. A value | |
91 | of 0 for <parameter>index</parameter> selects the first active | |
92 | uniform variable. Permissible values for | |
93 | <parameter>index</parameter> range from 0 to the number of | |
94 | active uniform variables minus 1.</para> | |
95 | ||
96 | <para>Shaders may use either built-in uniform variables, | |
97 | user-defined uniform variables, or both. Built-in uniform | |
98 | variables have a prefix of "gl_" and reference | |
99 | existing OpenGL state or values derived from such state (e.g., | |
100 | <parameter>gl_Fog</parameter>, | |
101 | <parameter>gl_ModelViewMatrix</parameter>, etc., see the OpenGL | |
102 | Shading Language specification for a complete list.) | |
103 | User-defined uniform variables have arbitrary names and obtain | |
104 | their values from the application through calls to | |
105 | <citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>. | |
106 | A uniform variable (either built-in or user-defined) is | |
107 | considered active if it is determined during the link operation | |
108 | that it may be accessed during program execution. Therefore, | |
109 | <parameter>program</parameter> should have previously been the | |
110 | target of a call to | |
111 | <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>, | |
112 | but it is not necessary for it to have been linked | |
113 | successfully.</para> | |
114 | ||
115 | <para>The size of the character buffer required to store the | |
116 | longest uniform variable name in <parameter>program</parameter> | |
117 | can be obtained by calling | |
118 | <citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry> | |
119 | with the value | |
120 | <constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant>. This value | |
121 | should be used to allocate a buffer of sufficient size to store | |
122 | the returned uniform variable name. The size of this character | |
123 | buffer is passed in <parameter>bufSize</parameter>, and a | |
124 | pointer to this character buffer is passed in | |
125 | <parameter>name.</parameter></para> | |
126 | ||
127 | <para><function>glGetActiveUniform</function> returns the name | |
128 | of the uniform variable indicated by | |
129 | <parameter>index</parameter>, storing it in the character buffer | |
130 | specified by <parameter>name</parameter>. The string returned | |
131 | will be null terminated. The actual number of characters written | |
132 | into this buffer is returned in <parameter>length</parameter>, | |
133 | and this count does not include the null termination character. | |
134 | If the length of the returned string is not required, a value of | |
135 | <constant>NULL</constant> can be passed in the | |
136 | <parameter>length</parameter> argument.</para> | |
137 | ||
138 | <para>The <parameter>type</parameter> | |
139 | argument will return a pointer to the uniform variable's data | |
140 | type. The symbolic constants | |
141 | <constant>GL_FLOAT</constant>, | |
142 | <constant>GL_FLOAT_VEC2</constant>, | |
143 | <constant>GL_FLOAT_VEC3</constant>, | |
144 | <constant>GL_FLOAT_VEC4</constant>, | |
145 | <constant>GL_INT</constant>, | |
146 | <constant>GL_INT_VEC2</constant>, | |
147 | <constant>GL_INT_VEC3</constant>, | |
148 | <constant>GL_INT_VEC4</constant>, | |
149 | <constant>GL_BOOL</constant>, | |
150 | <constant>GL_BOOL_VEC2</constant>, | |
151 | <constant>GL_BOOL_VEC3</constant>, | |
152 | <constant>GL_BOOL_VEC4</constant>, | |
153 | <constant>GL_FLOAT_MAT2</constant>, | |
154 | <constant>GL_FLOAT_MAT3</constant>, | |
155 | <constant>GL_FLOAT_MAT4</constant>, | |
156 | <constant>GL_FLOAT_MAT2x3</constant>, | |
157 | <constant>GL_FLOAT_MAT2x4</constant>, | |
158 | <constant>GL_FLOAT_MAT3x2</constant>, | |
159 | <constant>GL_FLOAT_MAT3x4</constant>, | |
160 | <constant>GL_FLOAT_MAT4x2</constant>, | |
161 | <constant>GL_FLOAT_MAT4x3</constant>, | |
162 | <constant>GL_SAMPLER_1D</constant>, | |
163 | <constant>GL_SAMPLER_2D</constant>, | |
164 | <constant>GL_SAMPLER_3D</constant>, | |
165 | <constant>GL_SAMPLER_CUBE</constant>, | |
166 | <constant>GL_SAMPLER_1D_SHADOW</constant>, or | |
167 | <constant>GL_SAMPLER_2D_SHADOW</constant> | |
168 | may be returned.</para> | |
169 | ||
170 | <para>If one or more elements of an array are active, the name | |
171 | of the array is returned in <parameter>name</parameter>, the | |
172 | type is returned in <parameter>type</parameter>, and the | |
173 | <parameter>size</parameter> parameter returns the highest array | |
174 | element index used, plus one, as determined by the compiler | |
175 | and/or linker. Only one active uniform variable will be reported | |
176 | for a uniform array.</para> | |
177 | ||
178 | <para>Uniform variables that are declared as structures or | |
179 | arrays of structures will not be returned directly by this | |
180 | function. Instead, each of these uniform variables will be | |
181 | reduced to its fundamental components containing the | |
182 | "." and "[]" operators such that each of the | |
183 | names is valid as an argument to | |
184 | <citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>. | |
185 | Each of these reduced uniform variables is counted as one active | |
186 | uniform variable and is assigned an index. A valid name cannot | |
187 | be a structure, an array of structures, or a subcomponent of a | |
188 | vector or matrix.</para> | |
189 | ||
190 | <para>The size of the uniform variable will be returned in | |
191 | <parameter>size</parameter>. Uniform variables other than arrays | |
192 | will have a size of 1. Structures and arrays of structures will | |
193 | be reduced as described earlier, such that each of the names | |
194 | returned will be a data type in the earlier list. If this | |
195 | reduction results in an array, the size returned will be as | |
196 | described for uniform arrays; otherwise, the size returned will | |
197 | be 1.</para> | |
198 | ||
199 | <para>The list of active uniform variables may include both | |
200 | built-in uniform variables (which begin with the prefix | |
201 | "gl_") as well as user-defined uniform variable | |
202 | names.</para> | |
203 | ||
204 | <para>This function will return as much information as it can | |
205 | about the specified active uniform variable. If no information | |
206 | is available, <parameter>length</parameter> will be 0, and | |
207 | <parameter>name</parameter> will be an empty string. This | |
208 | situation could occur if this function is called after a link | |
209 | operation that failed. If an error occurs, the return values | |
210 | <parameter>length</parameter>, <parameter>size</parameter>, | |
211 | <parameter>type</parameter>, and <parameter>name</parameter> | |
212 | will be unmodified.</para> | |
213 | </refsect1> | |
214 | <refsect1 id="notes"><title>Notes</title> | |
215 | <para><function>glGetActiveUniform</function> is available only | |
216 | if the GL version is 2.0 or greater.</para> | |
217 | ||
218 | <para><constant>GL_FLOAT_MAT2x3</constant>, | |
219 | <constant>GL_FLOAT_MAT2x4</constant>, | |
220 | <constant>GL_FLOAT_MAT3x2</constant>, | |
221 | <constant>GL_FLOAT_MAT3x4</constant>, | |
222 | <constant>GL_FLOAT_MAT4x2</constant>, and | |
223 | <constant>GL_FLOAT_MAT4x3</constant> | |
224 | will only be returned as a <parameter>type</parameter> | |
225 | if the GL version is 2.1 or greater.</para> | |
226 | </refsect1> | |
227 | <refsect1 id="errors"><title>Errors</title> | |
228 | <para><constant>GL_INVALID_VALUE</constant> is generated if | |
229 | <parameter>program</parameter> is not a value generated by | |
230 | OpenGL.</para> | |
231 | ||
232 | <para><constant>GL_INVALID_OPERATION</constant> is generated if | |
233 | <parameter>program</parameter> is not a program object.</para> | |
234 | ||
235 | <para><constant>GL_INVALID_VALUE</constant> is generated if | |
236 | <parameter>index</parameter> is greater than or equal to the | |
237 | number of active uniform variables in | |
238 | <parameter>program</parameter>.</para> | |
239 | ||
240 | <para><constant>GL_INVALID_OPERATION</constant> is generated if | |
241 | <function>glGetActiveUniform</function> is executed between the | |
242 | execution of | |
243 | <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> | |
244 | and the corresponding execution of | |
245 | <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</para> | |
246 | ||
247 | <para><constant>GL_INVALID_VALUE</constant> is generated if | |
248 | <parameter>bufSize</parameter> is less than 0.</para> | |
249 | </refsect1> | |
250 | <refsect1 id="associatedgets"><title>Associated Gets</title> | |
251 | <para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> | |
252 | with argument <constant>GL_MAX_VERTEX_UNIFORM_COMPONENTS | |
253 | </constant> or | |
254 | <constant>GL_MAX_FRAGMENT_UNIFORM_COMPONENTS</constant>.</para> | |
255 | ||
256 | <para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry> | |
257 | with argument <constant>GL_ACTIVE_UNIFORMS</constant> or | |
258 | <constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant>.</para> | |
259 | ||
260 | <para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para> | |
261 | </refsect1> | |
262 | <refsect1 id="seealso"><title>See Also</title> | |
263 | <para><citerefentry><refentrytitle>glGetUniform</refentrytitle></citerefentry>, | |
264 | <citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>, | |
265 | <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>, | |
266 | <citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>, | |
267 | <citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry></para> | |
268 | </refsect1> | |
269 | <refsect1 id="Copyright"><title>Copyright</title> | |
270 | <para> | |
271 | Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd. | |
272 | This material may be distributed subject to the terms and conditions set forth in | |
273 | the Open Publication License, v 1.0, 8 June 1999. | |
274 | <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>. | |
275 | </para> | |
276 | </refsect1> | |
277 | </refentry> |