glGetUniformLocation
3G

# glGetUniformLocation

Returns the location of a uniform variable

## C Specification

    		GLint glGetUniformLocation
    		GLuint program
    		const GLchar *name

## Parameters

`program`

  Specifies the program object to be queried.

`name`

  Points to a null terminated string containing the name of the uniform variable whose location is to be queried.

## Description

`glGetUniformLocation` returns an integer that represents the location of a specific uniform variable within 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` starts with the reserved prefix "gl_".

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. Except if the last part of `name` indicates a uniform variable array, the location of the first element of an array can be retrieved by using the name of the array, or by using the name appended by "[0]".

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.

## Notes

`glGetUniformLocation` is available only if the GL version is 2.0 or greater.

## Errors

`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.

`GL_INVALID_OPERATION` is generated if `glGetUniformLocation` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGetActiveUniform with arguments `program` and the index of an active uniform variable

glGetProgram with arguments `program` and `GL_ACTIVE_UNIFORMS` or `GL_ACTIVE_UNIFORM_MAX_LENGTH`

glGetUniform with arguments `program` and the name of a uniform variable

glIsProgram

## See Also

glLinkProgram, glUniform

## Copyright

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/.