2010 Khronos Group
glGetActiveUniformBlock 3G
glGetActiveUniformBlock query information about an active uniform block

## C Specification

void `glGetActiveUniformBlockiv` GLuint program GLuint uniformBlockIndex GLenum pname GLint *params

## Parameters

program

  Specifies the name of a program containing the uniform block.

uniformBlockIndex

  Specifies the index of the uniform block within program.

pname

  Specifies the name of the parameter to query.

params

  Specifies the address of a variable to receive the result of the query.

## Description

`glGetActiveUniformBlockiv` retrieves information about an active uniform block within program.

program must be the name of a program object for which the command glLinkProgram must have been called in the past, although it is not required that glLinkProgram must have succeeded. The link could have failed because the number of active uniforms exceeded the limit.

uniformBlockIndex is an active uniform block index of program, and must be less than the value of `GL_ACTIVE_UNIFORM_BLOCKS`.

Upon success, the uniform block parameter(s) specified by pname are returned in params. If an error occurs, nothing will be written to params.

If pname is `GL_UNIFORM_BLOCK_BINDING`, then the index of the uniform buffer binding point last selected by the uniform block specified by uniformBlockIndex for program is returned. If no uniform block has been previously specified, zero is returned.

If pname is `GL_UNIFORM_BLOCK_DATA_SIZE`, then the implementation-dependent minimum total buffer object size, in basic machine units, required to hold all active uniforms in the uniform block identified by uniformBlockIndex is returned. It is neither guaranteed nor expected that a given implementation will arrange uniform values as tightly packed in a buffer object. The exception to this is the std140 uniform block layout, which guarantees specific packing behavior and does not require the application to query for offsets and strides. In this case the minimum size may still be queried, even though it is determined in advance based only on the uniform block declaration.

If pname is `GL_UNIFORM_BLOCK_NAME_LENGTH`, then the total length (including the nul terminator) of the name of the uniform block identified by uniformBlockIndex is returned.

If pname is `GL_UNIFORM_BLOCK_ACTIVE_UNIFORMS`, then the number of active uniforms in the uniform block identified by uniformBlockIndex is returned.

If pname is `GL_UNIFORM_BLOCK_ACTIVE_UNIFORM_INDICES`, then a list of the active uniform indices for the uniform block identified by uniformBlockIndex is returned. The number of elements that will be written to params is the value of `GL_UNIFORM_BLOCK_ACTIVE_UNIFORMS` for uniformBlockIndex.

If pname is `GL_UNIFORM_BLOCK_REFERENCED_BY_VERTEX_SHADER`, `GL_UNIFORM_BLOCK_REFERENCED_BY_GEOMETRY_SHADER`, or `GL_UNIFORM_BLOCK_REFERENCED_BY_FRAGMENT_SHADER`, then a boolean value indicating whether the uniform block identified by uniformBlockIndex is referenced by the vertex, geometry, or fragment programming stages of program, respectively, is returned.

## Errors

`GL_INVALID_VALUE` is generated if uniformBlockIndex is greater than or equal to the value of `GL_ACTIVE_UNIFORM_BLOCKS` or is not the index of an active uniform block in program.

`GL_INVALID_ENUM` is generated if pname is not one of the accepted tokens.

`GL_INVALID_OPERATION` is generated if program is not the name of a program object for which glLinkProgram has been called in the past.

## Notes

`glGetActiveUniformBlockiv` is available only if the GL version is 3.1 or greater.

## See Also

glGetActiveUniformBlockName, glGetUniformBlockIndex, glLinkProgram

## Copyright

Copyright 2010-2013 Khronos Group. 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/.