  Synthesizing realistic human movements, dynamically responsive to the
environment, is a long-standing objective in character animation, with
applications in computer vision, sports, and healthcare, for motion prediction
and data augmentation. Recent kinematics-based generative motion models offer
impressive scalability in modeling extensive motion data, albeit without an
interface to reason about and interact with physics. While
simulator-in-the-loop learning approaches enable highly physically realistic
behaviors, the challenges in training often affect scalability and adoption. We
introduce DROP, a novel framework for modeling Dynamics Responses of humans
using generative mOtion prior and Projective dynamics. DROP can be viewed as a
highly stable, minimalist physics-based human simulator that interfaces with a
kinematics-based generative motion prior. Utilizing projective dynamics, DROP
allows flexible and simple integration of the learned motion prior as one of
the projective energies, seamlessly incorporating control provided by the
motion prior with Newtonian dynamics. Serving as a model-agnostic plug-in, DROP
enables us to fully leverage recent advances in generative motion models for
physics-based motion synthesis. We conduct extensive evaluations of our model
across different motion tasks and various physical perturbations, demonstrating
the scalability and diversity of responses.
