1. A method comprising: receiving an animation rig with a plurality of rig parameters, the rig parameters defining a deformation space for an attached surface mesh, the attached surface mesh comprising a plurality of nodes; receiving material stiffness data on a subset of the rig parameters, the material stiffness data defining a stiffness scale value for each of the subset of the rig parameters, wherein the stiffness scale value is relative to a stiffness of a homogeneous material chosen for a finite element method model derived from the attached surface mesh, using the rig and the material stiffness data to influence a physics-based simulation of the effects of one or more of gravity, inertia, and penalty-collisions on the subset of the rig parameters, wherein the physics-based simulation of the effects of one or more of gravity, inertia, and penalty-collisions is constrained by the deformation space of the rig; and generating a plurality of keyframes for some or all of the rig parameters of the animation rig as a result of the physics-based simulation of the effects of one or more of gravity, inertia, and penalty-collisions on the subset of the rig parameters.