Shangming Yang , Sch. of Comput. Sci. & Eng., Univ. of Electron. Sci. & Technol. of China, Chengdu, China

Zhang Yi , Coll. of Comput. Sci., Sichuan Univ., Chengdu, China

Mao Ye , Sch. of Comput. Sci. & Eng., Univ. of Electron. Sci. & Technol. of China, Chengdu, China

Xiaofei He , State Key Lab. of CAD&CG, Zhejiang Univ., Hangzhou, China