FEPR: fast energy projection for real-time simulation of deformable objects.

We propose a novel projection scheme that corrects energy fluctuations in simulations of deformable objects, thereby removing unwanted numerical dissipation and numerical "explosions". The key idea of our method is to first take a step using a conventional integrator, then project the result back to the constant energy-momentum manifold. We implement this strategy using fast projection, which only adds a small amount of overhead to existing physics-based solvers. We test our method with several implicit integration rules and demonstrate its benefits when used in conjunction with Position Based Dynamics and Projective Dynamics. When added to a dissipative integrator such as backward Euler, our method corrects the artificial damping and thus produces more vivid motion. Our projection scheme also effectively prevents instabilities that can arise due to approximate solves or large time steps. Our method is fast, stable, and easy to implement---traits that make it well-suited for real-time physics applications such as games or training simulators.