Huagen Wan Xiaogang Jin Hujun Bao Direct 3D Painting with a Metaball-Based Paintbrush. 100- 2000 15 J. Comput. Sci. Technol. 1 http://jcst.ict.ac.cn/cone/cone01.html#paper11 db/journals/jcst/jcst15.html#WanJB00