Collision Response

• time: backup to point of collision or deal with it at next time step?
• kinematic or dynamic response?
• rigid objects or flexible objects?
• need to calculate normal of contact surface
  • if point- or edge-plane contact: normal to plane
  • if edge-edge contact: cross product of edges
  • if point-point or point-edge: ignore contact

Common approaches to rigid object collisions

• Kinematic Response
  
  • Move to surface being penetrated
  • Negate motion component (normal to contact surface) that violates penetration constraint.
  • for 'bounce' negate velocity component that is normal to contact surface
• Dynamic penalty
  • Add force (e.g. spring) to penalize penetration (i.e., restore non-penetration)
  • Can introduce stiff equations, and therefore small time steps, into simulation
  • Need to set force so that penetration is eliminated after just a couple of frames but not over react so as to introduce large amounts of energy into the system
• Impluse force
  • Assume response of collision is that separating velocity, Vs, is some fraction of normal component of collision velocity: Vs = e*Vn
  • Vs is a function of linear velocity and rotational velocity
  • compute normal force at contact point of rigid object such that linear velocity and rotational velocity equal Vs

If flexible object, move point/edge to contact surface and compute force on deformable object.