Software Engineering Radio - the podcast for professional software developers SE Radio 739: Erin Catto on Video Game Physics Engines
Sep 23, 2026
Erin Catto, veteran game developer and creator of the open-source Box2D engine, explores the engineering behind video game physics. He covers collision detection, rigid-body simulation, friction, sleeping bodies, and simulation islands. The conversation also examines realism versus stability, CPU and SIMD optimization, deterministic replay, testing techniques, and the evolution from Box2D to the new 3D engine Box3D.
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The Four Stages Of A Physics Step
- Each simulation step typically proceeds through broad phase, narrow phase, solver, and transform updates.
- Bounding boxes cheaply cull potential pairs before computationally expensive geometry finds actual contact points.
Why Contact Points Create Realistic Rotation
- Physically resolving contacts requires impulses at contact points, not merely moving overlapping objects apart.
- The moment of inertia combines an object's shape and size with its mass to determine rotational response.
Game Physics Trades Exactness For Robustness
- Game physics approximates differential equations because real-time performance prevents exact solutions.
- Robustness matters as much as accuracy because games encounter unpredictable scenarios outside their tests.