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<div class="refentry" title="glBindAttribLocation"><a id="glBindAttribLocation"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glBindAttribLocation — Associates a generic vertex attribute index with a named attribute variable</p></div><div class="refsynopsisdiv" title="C Specification"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glBindAttribLocation</b>(</code></td><td>GLuint <var class="pdparam">program</var>, </td></tr><tr><td> </td><td>GLuint <var class="pdparam">index</var>, </td></tr><tr><td> </td><td>const GLchar *<var class="pdparam">name</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Parameters"><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 handle of the program object in
which the association is to be made.</p></dd><dt><span class="term"><em class="parameter"><code>index</code></em></span></dt><dd><p>Specifies the index of the generic vertex
attribute to be bound.</p></dd><dt><span class="term"><em class="parameter"><code>name</code></em></span></dt><dd><p>Specifies a null terminated string containing
the name of the vertex shader attribute variable to
which <em class="parameter"><code>index</code></em> is to be
bound.</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="description"></a><h2>Description</h2><p><code class="function">glBindAttribLocation</code> is used to
associate a user-defined attribute variable in the program
object specified by <em class="parameter"><code>program</code></em> with a
generic vertex attribute index. The name of the user-defined
attribute variable is passed as a null terminated string in
<em class="parameter"><code>name</code></em>. The generic vertex attribute index
to be bound to this variable is specified by
<em class="parameter"><code>index</code></em>. When
<em class="parameter"><code>program</code></em> is made part of current state,
values provided via the generic vertex attribute
<em class="parameter"><code>index</code></em> will modify the value of the
user-defined attribute variable specified by
<em class="parameter"><code>name</code></em>.</p><p>If <em class="parameter"><code>name</code></em> refers to a matrix
attribute variable, <em class="parameter"><code>index</code></em> refers to the
first column of the matrix. Other matrix columns are then
automatically bound to locations <em class="parameter"><code>index+1</code></em>
for a matrix of type <code class="function">mat2</code>; <em class="parameter"><code>index+1</code></em> and
<em class="parameter"><code>index+2</code></em> for a matrix of type <code class="function">mat3</code>; and
<em class="parameter"><code>index+1</code></em>, <em class="parameter"><code>index+2</code></em>,
and <em class="parameter"><code>index+3</code></em> for a matrix of type
<code class="function">mat4</code>.</p><p>This command makes it possible for vertex shaders to use
descriptive names for attribute variables rather than generic
variables that are numbered from 0 to
<code class="constant">GL_MAX_VERTEX_ATTRIBS</code> -1. The values sent
to each generic attribute index are part of current state.
If a different program object is made current by calling
<a class="citerefentry" href="glUseProgram"><span class="citerefentry"><span class="refentrytitle">glUseProgram</span></span></a>,
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
<em class="parameter"><code>index</code></em>.</p><p>Attribute variable
name-to-generic attribute index bindings for a program object
can be explicitly assigned at any time by calling
<code class="function">glBindAttribLocation</code>. Attribute bindings do
not go into effect until
<a class="citerefentry" href="glLinkProgram"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>
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.</p><p>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.</p></div><div class="refsect1" title="Notes"><a id="notes"></a><h2>Notes</h2><p><code class="function">glBindAttribLocation</code> 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.</p><p>If <em class="parameter"><code>name</code></em> 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.</p><p>Applications are allowed to bind more than one
user-defined attribute variable to the same generic vertex
attribute index. This is called <span class="emphasis"><em>aliasing</em></span>,
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.</p><p>Active attributes that are not explicitly bound will be
bound by the linker when
<a class="citerefentry" href="glLinkProgram"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>
is called. The locations assigned can be queried by calling
<a class="citerefentry" href="glGetAttribLocation"><span class="citerefentry"><span class="refentrytitle">glGetAttribLocation</span></span></a>.</p><p>OpenGL copies the <em class="parameter"><code>name</code></em> string when
<code class="function">glBindAttribLocation</code> is called, so an
application may free its copy of the <em class="parameter"><code>name</code></em>
string immediately after the function returns.</p><p>Generic attribute locations may be specified in the shader source
text using a <code class="function">location</code> layout qualifier. In this case,
the location of the attribute specified in the shader's source takes precedence
and may be queried by calling <a class="citerefentry" href="glGetAttribLocation"><span class="citerefentry"><span class="refentrytitle">glGetAttribLocation</span></span></a>.
</p></div><div class="refsect1" title="Errors"><a id="errors"></a><h2>Errors</h2><p><code class="constant">GL_INVALID_VALUE</code> is generated if
<em class="parameter"><code>index</code></em> is greater than or equal to
<code class="constant">GL_MAX_VERTEX_ATTRIBS</code>.</p><p><code class="constant">GL_INVALID_OPERATION</code> is generated if
<em class="parameter"><code>name</code></em> starts with the reserved prefix
"gl_".</p><p><code class="constant">GL_INVALID_VALUE</code> is generated if
<em class="parameter"><code>program</code></em> is not a value generated by
OpenGL.</p><p><code class="constant">GL_INVALID_OPERATION</code> is generated if
<em class="parameter"><code>program</code></em> is not a program object.</p></div><div class="refsect1" title="Associated Gets"><a id="associatedgets"></a><h2>Associated Gets</h2><p><a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>
with argument <code class="constant">GL_MAX_VERTEX_ATTRIBS</code></p><p><a class="citerefentry" href="glGetActiveAttrib"><span class="citerefentry"><span class="refentrytitle">glGetActiveAttrib</span></span></a>
with argument <em class="parameter"><code>program</code></em></p><p><a class="citerefentry" href="glGetAttribLocation"><span class="citerefentry"><span class="refentrytitle">glGetAttribLocation</span></span></a>
with arguments <em class="parameter"><code>program</code></em> and
<em class="parameter"><code>name</code></em></p><p><a class="citerefentry" href="glIsProgram"><span class="citerefentry"><span class="refentrytitle">glIsProgram</span></span></a></p></div><div class="refsect1" title="See Also"><a id="seealso"></a><h2>See Also</h2><p><a class="citerefentry" href="glDisableVertexAttribArray"><span class="citerefentry"><span class="refentrytitle">glDisableVertexAttribArray</span></span></a>,
<a class="citerefentry" href="glEnableVertexAttribArray"><span class="citerefentry"><span class="refentrytitle">glEnableVertexAttribArray</span></span></a>,
<a class="citerefentry" href="glUseProgram"><span class="citerefentry"><span class="refentrytitle">glUseProgram</span></span></a>,
<a class="citerefentry" href="glVertexAttrib"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,
<a class="citerefentry" href="glVertexAttribPointer"><span class="citerefentry"><span class="refentrytitle">glVertexAttribPointer</span></span></a></p></div><div class="refsect1" title="Copyright"><div id="Copyright"><h2>Copyright</h2><p>
Copyright © 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.
<a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
</p></div></div></div>