Wookash Podcast

What Makes a Good Physics Engine? | Erin Catto

Jul 25, 2026
Erin Catto, game physics engineer and creator of Box2D, talks about the origins of his physics work and how simple, robust algorithms changed game development. He discusses solver challenges, lifetime-safety handles, and the evolution from Box2D to a new Box3D for multiplayer. The conversation covers performance, stability trade-offs, and lessons from building physics-rich games like Legend of California.
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ADVICE

Use Handles With Generation Numbers

  • Prefer opaque handles and an ID+generation scheme over raw pointers to safely manage lifetime and detect stale references.
  • Erin's body ID encodes world index, body index and generation so dropped/reused indices are reliably detected.
ADVICE

Expose A Small Stable C API

  • Ship a plain C API for physics libraries to ease cross-language bindings and hide internal data layout.
  • Erin emphasizes C headers let you change internals without forcing users to recompile templates or parse headers.
INSIGHT

Wide SIMD Speeds Constraint Solving

  • Wide SIMD (processing multiple constraints in parallel with X/Y/Z lanes) delivers big solver throughput gains.
  • Erin solves four constraints at once using SIMD vectors arranged as separate X, Y, Z lanes for fast parallel math.
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