Hi John, I recall that, those ragdolls falling down stairs. From what I heard from a few Pixel employees, Pixar uses Bullet for some rigid body VFX effects, and

Hi John, I recall that, those ragdolls falling down stairs. From what I heard from a few Pixel employees, Pixar uses Bullet for some rigid body VFX effects, and Bullet still uses velocity-level LCP in combination with maximal coordinate constraints or with Featherstone-style reduced coordinate forward dynamics. The impulse/velocity-based contact model allows to model arbitrary soft contact (using contact force mixing (CFM) and error reduction parameter (ERP) terms), similar to spring-damper or MuJoCo-style contact (for MuJoCo see https://mujoco.readthedocs.io/en/latest/computation.html https://mujoco.readthedocs.io/en/latest/computation.html and https://github.com/deepmind/mujoco https://github.com/deepmind/mujoco). For the last 10 years we use this also for robotics simulation for quadruped robots and robot arm grasping contact. Check out Erin Catto's presentation about re-inventing soft springs in this PDF: https://box2d.org/files/ErinCatto_SoftConstraints_GDC2011.pdf https://box2d.org/files/ErinCatto_SoftConstraints_GDC2011.pd... Furthermore, impulse/velocity-level LCP based constraint solving can be combined with finite element method (FEM) or mass-spring based deformable contact solving if higher-accuracy contact and friction modeling is needed.