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197 lines
9 KiB
XML
197 lines
9 KiB
XML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glBindAttribLocation">
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<refmeta>
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<refentrytitle>glBindAttribLocation</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glBindAttribLocation</refname>
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<refpurpose>Associates a generic vertex attribute index with a named attribute variable</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glBindAttribLocation</function></funcdef>
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<paramdef>GLuint <parameter>program</parameter></paramdef>
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<paramdef>GLuint <parameter>index</parameter></paramdef>
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<paramdef>const GLchar *<parameter>name</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>program</parameter></term>
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<listitem>
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<para>Specifies the handle of the program object in
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which the association is to be made.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>index</parameter></term>
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<listitem>
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<para>Specifies the index of the generic vertex
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attribute to be bound.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>name</parameter></term>
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<listitem>
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<para>Specifies a null terminated string containing
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the name of the vertex shader attribute variable to
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which <parameter>index</parameter> is to be
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bound.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para><function>glBindAttribLocation</function> is used to
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associate a user-defined attribute variable in the program
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object specified by <parameter>program</parameter> with a
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generic vertex attribute index. The name of the user-defined
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attribute variable is passed as a null terminated string in
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<parameter>name</parameter>. The generic vertex attribute index
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to be bound to this variable is specified by
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<parameter>index</parameter>. When
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<parameter>program</parameter> is made part of current state,
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values provided via the generic vertex attribute
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<parameter>index</parameter> will modify the value of the
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user-defined attribute variable specified by
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<parameter>name</parameter>.</para>
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<para>If <parameter>name</parameter> refers to a matrix
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attribute variable, <parameter>index</parameter> refers to the
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first column of the matrix. Other matrix columns are then
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automatically bound to locations <parameter>index+1</parameter>
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for a matrix of type mat2; <parameter>index+1</parameter> and
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<parameter>index+2</parameter> for a matrix of type mat3; and
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<parameter>index+1</parameter>, <parameter>index+2</parameter>,
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and <parameter>index+3</parameter> for a matrix of type
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mat4.</para>
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<para>This command makes it possible for vertex shaders to use
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descriptive names for attribute variables rather than generic
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variables that are numbered from 0 to
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<constant>GL_MAX_VERTEX_ATTRIBS</constant> -1. The values sent
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to each generic attribute index are part of current state, just
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like standard vertex attributes such as color, normal, and
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vertex position. If a different program object is made current
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by calling
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<citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry>,
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the generic vertex attributes are tracked in such a way that the
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same values will be observed by attributes in the new program
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object that are also bound to
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<parameter>index</parameter>.</para> <para>Attribute variable
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name-to-generic attribute index bindings for a program object
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can be explicitly assigned at any time by calling
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<function>glBindAttribLocation</function>. Attribute bindings do
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not go into effect until
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<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>
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is called. After a program object has been linked successfully,
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the index values for generic attributes remain fixed (and their
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values can be queried) until the next link command
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occurs.</para>
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<para>Applications are not allowed to bind any of the standard
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OpenGL vertex attributes using this command, as they are bound
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automatically when needed. Any attribute binding that occurs
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after the program object has been linked will not take effect
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until the next time the program object is linked.</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para><function>glBindAttribLocation</function> is available
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only if the GL version is 2.0 or greater.</para>
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<para><function>glBindAttribLocation</function> can be called
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before any vertex shader objects are bound to the specified
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program object. It is also permissible to bind a generic
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attribute index to an attribute variable name that is never used
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in a vertex shader.</para>
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<para>If <parameter>name</parameter> was bound previously, that
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information is lost. Thus you cannot bind one user-defined
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attribute variable to multiple indices, but you can bind
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multiple user-defined attribute variables to the same
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index.</para>
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<para>Applications are allowed to bind more than one
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user-defined attribute variable to the same generic vertex
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attribute index. This is called <emphasis>aliasing</emphasis>,
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and it is allowed only if just one of the aliased attributes is
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active in the executable program, or if no path through the
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shader consumes more than one attribute of a set of attributes
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aliased to the same location. The compiler and linker are
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allowed to assume that no aliasing is done and are free to
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employ optimizations that work only in the absence of aliasing.
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OpenGL implementations are not required to do error checking to
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detect aliasing. Because there is no way to bind standard
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attributes, it is not possible to alias generic attributes with
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conventional ones (except for generic attribute 0).</para>
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<para>Active attributes that are not explicitly bound will be
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bound by the linker when
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<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>
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is called. The locations assigned can be queried by calling
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<citerefentry><refentrytitle>glGetAttribLocation</refentrytitle></citerefentry>.</para>
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<para>OpenGL copies the <parameter>name</parameter> string when
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<function>glBindAttribLocation</function> is called, so an
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application may free its copy of the <parameter>name</parameter>
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string immediately after the function returns.</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>index</parameter> is greater than or equal to
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<constant>GL_MAX_VERTEX_ATTRIBS</constant>.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if
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<parameter>name</parameter> starts with the reserved prefix
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"gl_".</para>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>program</parameter> is not a value generated by
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OpenGL.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if
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<parameter>program</parameter> is not a program object.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if
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<function>glBindAttribLocation</function> is executed between
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the execution of
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<citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
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and the corresponding execution of
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<citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with argument <constant>GL_MAX_VERTEX_ATTRIBS</constant></para>
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<para><citerefentry><refentrytitle>glGetActiveAttrib</refentrytitle></citerefentry>
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with argument <parameter>program</parameter></para>
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<para><citerefentry><refentrytitle>glGetAttribLocation</refentrytitle></citerefentry>
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with arguments <parameter>program</parameter> and
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<parameter>name</parameter></para>
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<para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para><citerefentry><refentrytitle>glDisableVertexAttribArray</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glEnableVertexAttribArray</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glUseProgram</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glVertexAttrib</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glVertexAttribPointer</refentrytitle></citerefentry></para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd.
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This material may be distributed subject to the terms and conditions set forth in
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the Open Publication License, v 1.0, 8 June 1999.
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<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
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</para>
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</refsect1>
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</refentry>
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