Juraj Obert Fabio Pellacini Sumanta N. Pattanaik Visibility Editing For All-Frequency Shadow Design. 1441-1449 2010 29 Comput. Graph. Forum 4 http://dx.doi.org/10.1111/j.1467-8659.2010.01741.x db/journals/cgf/cgf29.html#ObertPP10