Gl.BindAttribLocation (gb.opengl.glsl)
Static Sub BindAttribLocation ( Program As Integer, Index As Integer, Name As String )
Associates a generic vertex attribute index with a named attribute variable.
Parameters
- program
-
Specifies the handle of the program object in
which the association is to be made.
- index
-
Specifies the index of the generic vertex
attribute to be bound.
- name
-
Specifies a null terminated string containing
the name of the vertex shader attribute variable to
which index is to be
bound.
Description
Gl.BindAttribLocation is used to
associate a user-defined attribute variable in the program
object specified by
program with a
generic vertex attribute index. The name of the user-defined
attribute variable is passed as a null terminated string in
name. The generic vertex attribute index
to be bound to this variable is specified by
index. When
program is made part of current state,
values provided via the generic vertex attribute
index will modify the value of the
user-defined attribute variable specified by
name.
If
name refers to a matrix
attribute variable,
index refers to the
first column of the matrix. Other matrix columns are then
automatically bound to locations
index+1
for a matrix of type
mat2;
index+1 and
index+2 for a matrix of type
mat3; and
index+1,
index+2,
and
index+3 for a matrix of type
mat4.
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
Gl.MAX_VERTEX_ATTRIBS -1. The values sent
to each generic attribute index are part of current state.
If a different program object is made current by calling
Glu.seProgram,
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
index.
Attribute variable
name-to-generic attribute index bindings for a program object
can be explicitly assigned at any time by calling
Gl.BindAttribLocation. Attribute bindings do
not go into effect until
Gl.LinkProgram
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.
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.
Notes
Gl.BindAttribLocation 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.
If
name 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.
Applications are allowed to bind more than one
user-defined attribute variable to the same generic vertex
attribute index. This is called
aliasing,
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.
Active attributes that are not explicitly bound will be
bound by the linker when
Gl.LinkProgram
is called. The locations assigned can be queried by calling
Gl.GetAttribLocation.
OpenGL copies the
name string when
Gl.BindAttribLocation is called, so an
application may free its copy of the
name
string immediately after the function returns.
Generic attribute locations may be specified in the shader source
text using a
location layout qualifier. In this case,
the location of the attribute specified in the shader's source takes precedence
and may be queried by calling Gl.GetAttribLocation.
Errors
Gl.INVALID_VALUE is generated if
index is greater than or equal to
Gl.MAX_VERTEX_ATTRIBS.
Gl.INVALID_OPERATION is generated if
name starts with the reserved prefix
"gl_".
Gl.INVALID_VALUE is generated if
program is not a value generated by
OpenGL.
Gl.INVALID_OPERATION is generated if
program is not a program object.
Associated Gets
Gl.Get
with argument Gl.MAX_VERTEX_ATTRIBS
Gl.GetActiveAttrib
with argument
program
Gl.GetAttribLocation
with arguments
program and
name
Gl.IsProgram
See also
Gl.DisableVertexAttribArray,
Gl.EnableVertexAttribArray,
Glu.seProgram,
Gl.VertexAttrib,
Gl.VertexAttribPointer