  Mil2 pushes the performance of high-resolution cloth simulation, making the
simulation interactive (in milliseconds) for models with one million degrees of
freedom (DOFs) while keeping every triangle untangled. The guarantee of being
penetration-free is inspired by the interior-point method, which converts the
inequality constraints to barrier potentials. Nevertheless, we propose a major
overhaul of this modality by defining a novel and simple barrier formulation
which does not depend on the distance between mesh primitives. Such a
non-distance barrier model allows a new way to integrate collision detection
into the simulation pipeline. Another contributor to the performance boost
comes from the so-called subspace reuse strategy. This is based on the
observation that low-frequency strain vibrations are near orthogonal to the
deformation induced by collisions or self-collisions, often of high frequency.
Subspace reuse then takes care of low-frequency residuals, while high-frequency
residuals can also be effectively smoothed by GPU-based iterative solvers. We
show that our method outperforms existing fast cloth simulators by nearly one
order while keeping the entire simulation penetration-free and producing
high-equality animations of high-resolution models.
