A faceted polygon ("crystal") is a rigid body with position, velocity, rotation and angular velocity. Each step, gravity accelerates it downward; when its lowest vertex crosses the floor or a wall, the penetration is pushed back out and the normal velocity component is reflected and scaled by the restitution slider (0 = sticks, 0.95 = near-perfectly elastic), while a small torque and friction term come from how far the contact point sits from the body's centre — off-centre hits make it tumble, centred hits bounce straight.
- Drag — grab the crystal and throw it; the release velocity is measured from your last few pointer movements.
- Kick — applies a sideways + upward impulse scaled by mass (impulse = mass × Δv), same as a real collision.
- Energy — kinetic (½mv² + ½Iω²) plus gravitational potential (mgh) relative to the floor; it drops on every inelastic bounce and jumps up on every kick.