Graphics Reference
In-Depth Information
In OpenGL ES 3.0, three approaches may be used to map a generic vertex
attribute index to an attribute variable name in the vertex shader. These
approaches can be categorized as follows:
• The index can be specified in the vertex shader source code using the
layout(location = N)
qualifier (recommended).
• OpenGL ES 3.0 will bind the generic vertex attribute index to the
attribute name.
• The application can bind the vertex attribute index to an attribute
name.
The easiest way to bind attributes to a location is to simply use the
layout(location = N)
qualifier; this approach requires the least amount
of code. However, in some cases, the other two options might be more
desirable. The
glBindAttribLocation
command can be used to bind a
generic vertex attribute index to an attribute variable in a vertex shader.
This binding takes effect when the program is linked the next time—it
does not change the bindings used by the currently linked program.
void
glBindAttribLocation
(GLuint
program
, GLuint
index
,
const GLchar *
name
)
program
name of a program object
index
generic vertex attribute index
name
name of the attribute variable
If
name
was bound previously, its assigned binding is replaced with an
index.
glBindAttribLocation
can be called even before a vertex shader
is attached to a program object. As a consequence, this call can be used
to bind any attribute name. Attribute names that do not exist or are not
active in a vertex shader attached to the program object are ignored.
Another option is to let OpenGL ES 3.0 bind the attribute variable name
to a generic vertex attribute index. This binding is performed when the
program is linked. In the linking phase, the OpenGL ES 3.0 implementation
performs the following operation for each attribute variable:
For each attribute variable, check whether a binding has been specified via
glBindAttribLocation
. If a binding is specified, the appropriate attribute
index specified is used. If not, the implementation will assign a generic vertex
attribute index.
