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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="glBindAttribLocation">
<refentryinfo>
<copyright>
<year>2003-2005</year>
<holder>3Dlabs Inc. Ltd.</holder>
</copyright>
<copyright>
<year>2010-2013</year>
<holder>Khronos Group</holder>
</copyright>
</refentryinfo>
<refmeta>
<refentrytitle>glBindAttribLocation</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glBindAttribLocation</refname>
<refpurpose>Associates a generic vertex attribute index with a named attribute variable</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glBindAttribLocation</function></funcdef>
<paramdef>GLuint <parameter>program</parameter></paramdef>
<paramdef>GLuint <parameter>index</parameter></paramdef>
<paramdef>const 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 handle of the program object in
which the association is to be made.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>index</parameter></term>
<listitem>
<para>Specifies the index of the generic vertex
attribute to be bound.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>name</parameter></term>
<listitem>
<para>Specifies a null terminated string containing
the name of the vertex shader attribute variable to
which <parameter>index</parameter> is to be
bound.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para><function>glBindAttribLocation</function> is used to
associate a user-defined attribute variable in the program
object specified by <parameter>program</parameter> with a
generic vertex attribute index. The name of the user-defined
attribute variable is passed as a null terminated string in
<parameter>name</parameter>. The generic vertex attribute index
to be bound to this variable is specified by
<parameter>index</parameter>. When
<parameter>program</parameter> is made part of current state,
values provided via the generic vertex attribute
<parameter>index</parameter> will modify the value of the
user-defined attribute variable specified by
<parameter>name</parameter>.</para>
<para>If <parameter>name</parameter> refers to a matrix
attribute variable, <parameter>index</parameter> refers to the
first column of the matrix. Other matrix columns are then
automatically bound to locations <parameter>index+1</parameter>
for a matrix of type <function>mat2</function>; <parameter>index+1</parameter> and
<parameter>index+2</parameter> for a matrix of type <function>mat3</function>; and
<parameter>index+1</parameter>, <parameter>index+2</parameter>,
and <parameter>index+3</parameter> for a matrix of type
<function>mat4</function>.</para>
<para>This command makes it possible for vertex shaders to use
descriptive names for attribute variables rather than generic
variables that are numbered from zero to the value of
<constant>GL_MAX_VERTEX_ATTRIBS</constant> minus one. The values sent
to each generic attribute index are part of current state.
If a different program object is made current by calling
<citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry>,
the generic vertex attributes are tracked in such a way that the
same values will be observed by attributes in the new program
object that are also bound to
<parameter>index</parameter>.</para> <para>Attribute variable
name-to-generic attribute index bindings for a program object
can be explicitly assigned at any time by calling
<function>glBindAttribLocation</function>. Attribute bindings do
not go into effect until
<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>
is called. After a program object has been linked successfully,
the index values for generic attributes remain fixed (and their
values can be queried) until the next link command
occurs.</para>
<para>Any attribute binding that occurs after the program object has been linked will not take effect
until the next time the program object is linked.</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para><function>glBindAttribLocation</function> can be called
before any vertex shader objects are bound to the specified
program object. It is also permissible to bind a generic
attribute index to an attribute variable name that is never used
in a vertex shader.</para>
<para>If <parameter>name</parameter> was bound previously, that
information is lost. Thus you cannot bind one user-defined
attribute variable to multiple indices, but you can bind
multiple user-defined attribute variables to the same
index.</para>
<para>Applications are allowed to bind more than one
user-defined attribute variable to the same generic vertex
attribute index. This is called <emphasis>aliasing</emphasis>,
and it is allowed only if just one of the aliased attributes is
active in the executable program, or if no path through the
shader consumes more than one attribute of a set of attributes
aliased to the same location. The compiler and linker are
allowed to assume that no aliasing is done and are free to
employ optimizations that work only in the absence of aliasing.
OpenGL implementations are not required to do error checking to
detect aliasing.</para>
<para>Active attributes that are not explicitly bound will be
bound by the linker when
<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>
is called. The locations assigned can be queried by calling
<citerefentry><refentrytitle>glGetAttribLocation</refentrytitle></citerefentry>.</para>
<para>OpenGL copies the <parameter>name</parameter> string when
<function>glBindAttribLocation</function> is called, so an
application may free its copy of the <parameter>name</parameter>
string immediately after the function returns.</para>
<para>Generic attribute locations may be specified in the shader source
text using a <function>location</function> layout qualifier. In this case,
the location of the attribute specified in the shader's source takes precedence
and may be queried by calling <citerefentry><refentrytitle>glGetAttribLocation</refentrytitle></citerefentry>.
</para>
</refsect1>
<refsect1 id="errors"><title>Errors</title>
<para><constant>GL_INVALID_VALUE</constant> is generated if
<parameter>index</parameter> is greater than or equal to
<constant>GL_MAX_VERTEX_ATTRIBS</constant>.</para>
<para><constant>GL_INVALID_OPERATION</constant> is generated if
<parameter>name</parameter> starts with the reserved prefix
"gl_".</para>
<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>
</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>glGetActiveAttrib</refentrytitle></citerefentry>
with argument <parameter>program</parameter></para>
<para><citerefentry><refentrytitle>glGetAttribLocation</refentrytitle></citerefentry>
with arguments <parameter>program</parameter> and
<parameter>name</parameter></para>
<para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para><citerefentry><refentrytitle>glDisableVertexAttribArray</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glEnableVertexAttribArray</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glUseProgram</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.
Copyright <trademark class="copyright"></trademark> 2010-2013 Khronos Group.
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>
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