Collision Response

When bodies collide, separate them and apply impulse for bounce.

Position correction: push apart along normal by penetration depth.

inv_mass = 1/mass for finite mass; 0 for static (immovable). The 0.8 factor (slop): slowly correct over multiple frames to avoid jitter.

Impulse: instantaneous change in velocity to simulate bounce.

This conserves momentum and produces realistic bouncing.

Friction:

• Tangent direction: perpendicular to normal in plane of motion.
• Tangential impulse: limited by Coulomb friction (μ * normal_impulse).

Produces sliding behavior.

Restitution (e):

• 1.0: bouncy ball.
• 0.5: rubber.
• 0.0: clay (no bounce, sticks).

In real games: tuned per material.

Static vs dynamic bodies:

• Static: inv_mass = 0, doesn't move (walls, floors).
• Dynamic: full simulation.
• Kinematic: scripted movement, no force-driven.

For our toy: handle 2D rigid bodies, support all three types.