1. School of Artificial Intelligence, Beijing University of Posts and Telecommunications, Beijing, China
2. State Key Lab of CAD&CG, College of Computer Science and Technology, Zhejiang University, Hangzhou, China
3. Department of Computer Science, ETH Zürich, Zürich, Switzerland
4. National Engineering Research Center of Visual Technology, School of Computer Science and Institute for Artificial Intelligence, Peking University, Beijing, China