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+<?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="glGetActiveAttrib">
+ <refmeta>
+ <refentrytitle>glGetActiveAttrib</refentrytitle>
+ <manvolnum>3G</manvolnum>
+ </refmeta>
+ <refnamediv>
+ <refname>glGetActiveAttrib</refname>
+ <refpurpose>Returns information about an active attribute variable for the specified program object</refpurpose>
+ </refnamediv>
+ <refsynopsisdiv><title>C Specification</title>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>void <function>glGetActiveAttrib</function></funcdef>
+ <paramdef>GLuint <parameter>program</parameter></paramdef>
+ <paramdef>GLuint <parameter>index</parameter></paramdef>
+ <paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
+ <paramdef>GLsizei *<parameter>length</parameter></paramdef>
+ <paramdef>GLint *<parameter>size</parameter></paramdef>
+ <paramdef>GLenum *<parameter>type</parameter></paramdef>
+ <paramdef>GLchar *<parameter>name</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>index</parameter></term>
+ <listitem>
+ <para>Specifies the index of the attribute variable
+ to be queried.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>bufSize</parameter></term>
+ <listitem>
+ <para>Specifies the maximum number of characters
+ OpenGL is allowed to write in the character buffer
+ indicated by <parameter>name</parameter>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>length</parameter></term>
+ <listitem>
+ <para>Returns the number of characters actually
+ written by OpenGL in the string indicated by
+ <parameter>name</parameter> (excluding the null
+ terminator) if a value other than
+ <constant>NULL</constant> is passed.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>size</parameter></term>
+ <listitem>
+ <para>Returns the size of the attribute
+ variable.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>type</parameter></term>
+ <listitem>
+ <para>Returns the data type of the attribute
+ variable.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>name</parameter></term>
+ <listitem>
+ <para>Returns a null terminated string containing
+ the name of the attribute variable.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+ <refsect1 id="description"><title>Description</title>
+ <para><function>glGetActiveAttrib</function> returns information
+ about an active attribute variable in the program object
+ specified by <parameter>program</parameter>. The number of
+ active attributes can be obtained by calling
+ <citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
+ with the value <constant>GL_ACTIVE_ATTRIBUTES</constant>. A
+ value of 0 for <parameter>index</parameter> selects the first
+ active attribute variable. Permissible values for
+ <parameter>index</parameter> range from 0 to the number of
+ active attribute variables minus 1.</para>
+
+ <para>A vertex shader may use either built-in attribute
+ variables, user-defined attribute variables, or both. Built-in
+ attribute variables have a prefix of "gl_" and
+ reference conventional OpenGL vertex attribtes (e.g.,
+ <parameter>gl_Vertex</parameter>,
+ <parameter>gl_Normal</parameter>, etc., see the OpenGL Shading
+ Language specification for a complete list.) User-defined
+ attribute variables have arbitrary names and obtain their values
+ through numbered generic vertex attributes. An attribute
+ 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,
+ <parameter>program</parameter> should have previously been the
+ target of a call to
+ <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
+ but it is not necessary for it to have been linked
+ successfully.</para>
+
+ <para>The size of the character buffer required to store the
+ longest attribute variable name in
+ <parameter>program</parameter> can be obtained by calling
+ <citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
+ with the value
+ <constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>. This value
+ should be used to allocate a buffer of sufficient size to store
+ the returned attribute name. The size of this character buffer
+ is passed in <parameter>bufSize</parameter>, and a pointer to
+ this character buffer is passed in
+ <parameter>name</parameter>.</para>
+
+ <para><function>glGetActiveAttrib</function> returns the name of
+ the attribute variable indicated by
+ <parameter>index</parameter>, storing it in the character buffer
+ specified by <parameter>name</parameter>. The string returned
+ will be null terminated. The actual number of characters written
+ into this buffer is returned in <parameter>length</parameter>,
+ and this count does not include the null termination character.
+ If the length of the returned string is not required, a value of
+ <constant>NULL</constant> can be passed in the
+ <parameter>length</parameter> argument.</para>
+
+ <para>The <parameter>type</parameter> argument will return a
+ pointer to the attribute variable's data type. The symbolic
+ constants <constant>GL_FLOAT</constant>,
+ <constant>GL_FLOAT_VEC2</constant>,
+ <constant>GL_FLOAT_VEC3</constant>,
+ <constant>GL_FLOAT_VEC4</constant>,
+ <constant>GL_FLOAT_MAT2</constant>,
+ <constant>GL_FLOAT_MAT3</constant>,
+ <constant>GL_FLOAT_MAT4</constant>,
+ <constant>GL_FLOAT_MAT2x3</constant>,
+ <constant>GL_FLOAT_MAT2x4</constant>,
+ <constant>GL_FLOAT_MAT3x2</constant>,
+ <constant>GL_FLOAT_MAT3x4</constant>,
+ <constant>GL_FLOAT_MAT4x2</constant>, or
+ <constant>GL_FLOAT_MAT4x3</constant> may be returned. The
+ <parameter>size</parameter> argument will return the size of the
+ attribute, in units of the type returned in
+ <parameter>type</parameter>.</para>
+
+ <para>The list of active attribute variables may include both
+ built-in attribute variables (which begin with the prefix
+ "gl_") as well as user-defined attribute variable
+ names.</para>
+
+ <para>This function will return as much information as it can
+ about the specified active attribute variable. If no information
+ is available, <parameter>length</parameter> will be 0, and
+ <parameter>name</parameter> 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
+ <parameter>length</parameter>, <parameter>size</parameter>,
+ <parameter>type</parameter>, and <parameter>name</parameter>
+ will be unmodified.</para>
+ </refsect1>
+ <refsect1 id="notes"><title>Notes</title>
+ <para><function>glGetActiveAttrib</function>
+ is available only if the GL version is 2.0 or greater.</para>
+
+ <para><constant>GL_FLOAT_MAT2x3</constant>,
+ <constant>GL_FLOAT_MAT2x4</constant>,
+ <constant>GL_FLOAT_MAT3x2</constant>,
+ <constant>GL_FLOAT_MAT3x4</constant>,
+ <constant>GL_FLOAT_MAT4x2</constant>, and
+ <constant>GL_FLOAT_MAT4x3</constant>
+ will only be returned as a <parameter>type</parameter>
+ if the GL version is 2.1 or greater.</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_VALUE</constant> is generated if
+ <parameter>index</parameter> is greater than or equal to the
+ number of active attribute variables in
+ <parameter>program</parameter>.</para>
+
+ <para><constant>GL_INVALID_OPERATION</constant> is generated if
+ <function>glGetActiveAttrib</function> is executed between the
+ execution of
+ <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
+ and the corresponding execution of
+ <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</para>
+
+ <para><constant>GL_INVALID_VALUE</constant> is generated if
+ <parameter>bufSize</parameter> is less than 0.</para>
+ </refsect1>
+ <refsect1 id="associatedgets"><title>Associated Gets</title>
+ <para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
+ with argument <constant>GL_MAX_VERTEX_ATTRIBS</constant>.</para>
+
+ <para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
+ with argument <constant>GL_ACTIVE_ATTRIBUTES</constant> or
+ <constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>.</para>
+
+ <para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
+ </refsect1>
+ <refsect1 id="seealso"><title>See Also</title>
+ <para><citerefentry><refentrytitle>glBindAttribLocation</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glVertexAttrib</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glVertexAttribPointer</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>
HCoop / clinton / guile-figl.git / blobdiff