Direct Manipulation of Subdivision Surfaces on GPU

We present an algorithm for interactive deformation of subdivision surfaces, including displaced subdivision surfaces and subdivision surfaces with geometric textures. Our system lets the user directly manipulate the surface using freely-selected surface points as handles. During deformation the control mesh vertices are automatically adjusted such that the deforming surface satisfies the handle position constraints while preserving the original surface shape and details. To best preserve surface details, we develop a gradient domain technique that incorporates the handle position constraints and detail preserving objectives into the deformation energy. For displaced subdivision surfaces and surfaces with geometric textures, the deformation energy is highly nonlinear and cannot be handled with existing iterative solvers. To address this issue, we introduce a shell deformation solver, which replaces each numerically unstable iteration step with two stable mesh deformation operations. Our deformation algorithm only uses local operations and is thus suitable for GPU implementation. The result is a real-time deformation system running orders of magnitude faster than the state-of-the-art multigrid mesh deformation solver. We demonstrate our technique with a variety of examples, including examples of creating visually pleasing character animations in real-time by driving a subdivision surface with motion capture data.