glGetUniformLocation — Returns the location of a uniform variable
GLint glGetUniformLocation( | GLuint program, |
const GLchar *name); |
programSpecifies the program object to be queried.
namePoints to a null terminated string containing the name of the uniform variable whose location is to be queried.
glGetUniformLocation returns an
integer that represents the location of a specific uniform
variable within a the default uniform block of a program object.
name must be a null terminated string
that contains no white space. name must
be an active uniform variable name in program
that is not a structure, an array of structures, or a subcomponent
of a vector or a matrix. This function returns -1 if
name does not correspond to an active uniform variable in
program or if name
is associated with a named uniform block.
Uniform variables that are structures or arrays of
structures may be queried by calling
glGetUniformLocation for each field within
the structure. The array element operator "[]" and the
structure field operator "." may be used in
name in order to select elements within
an array or fields within a structure. The result of using these
operators is not allowed to be another structure, an array of
structures, or a subcomponent of a vector or a matrix.
The first element of a uniform array is identified using the name
of the uniform array appended with "[0]". If the last part
of the string name indicates a uniform array, then the location of the
first element of that array can be retrieved by either using the name of
the array, or by using the name appended by "[0]".
Locations for sequential array indices are not required to be sequential. The location for "a[1]" may or may not be equal to the location for "a[0]" + 1. Furthermore, since unused elements at the end of uniform arrays may be trimmed the location of the i + 1 array element may not be valid even if the location of the i element is valid. As a direct consequence, the value of the location of "a[0]" + 1 may refer to a different uniform entirely. Applications that wish to set individual array elements should query the locations of each element separately.
The actual locations assigned to uniform variables are not
known until the program object is linked successfully. After
linking has occurred, the command
glGetUniformLocation can be used to obtain
the location of a uniform variable. This location value can then
be passed to
glUniform
to set the value of the uniform variable or to
glGetUniform
in order to query the current value of the uniform variable.
After a program object has been linked successfully, the index
values for uniform variables remain fixed until the next link
command occurs. Uniform variable locations and values can only
be queried after a link if the link was successful.
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.
GL_INVALID_OPERATION is generated if
program has not been successfully
linked.
glGetActiveUniform
with arguments program and the index of
an active uniform variable
glGetProgramiv
with arguments program and
GL_ACTIVE_UNIFORMS or
GL_ACTIVE_UNIFORM_MAX_LENGTH
glGetUniform
with arguments program and the name of a
uniform variable
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. http://opencontent.org/openpub/.