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glGetActiveUniformBlock - query information about an active uniform block
void glGetActiveUniformBlockiv(GLuint program, GLuint uniformBlockIndex, GLenum pname, GLint *params);
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.
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.
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.
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.
glGetActiveUniformBlockName(), glGetUniformBlockIndex(), glLinkProgram()
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