NAME

       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_TESS_CONTROL_SHADER,
       GL_UNIFORM_BLOCK_REFERENCED_BY_TESS_EVALUATION_SHADER, GL_UNIFORM_BLOCK_REFERENCED_BY_GEOMETRY_SHADER,
       GL_UNIFORM_BLOCK_REFERENCED_BY_FRAGMENT_SHADER, or GL_UNIFORM_BLOCK_REFERENCED_BY_COMPUTE_SHADER then a
       boolean value indicating whether the uniform block identified by uniformBlockIndex is referenced by the
       vertex, tessellation control, tessellation evaluation, geometry, fragment or compute 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.

       GL_UNIFORM_BLOCK_REFERENCED_BY_COMPUTE_SHADER is accepted only if the GL version is 4.3 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/.

AUTHORS

       opengl.org

opengl.org                                         10/22/2013                           GLGETACTIVEUNIFORMBL(3G)