Implement a physics engine (C or Zig)

Current State

The engine has no physics. engine/components/RigidBodyComponent.zig and ColliderComponent.zig are stubs with no backing simulation.

Split: this issue is now Phase 1 — backend + rigid bodies + collision. Queries, triggers, and debug visualization moved to the follow-up #34 to keep this shippable.

Goal (Phase 1)

Pick a physics backend (C or Zig, no C++ runtime dependency), wrap it, and get rigid bodies colliding under gravity, driven by the existing components.

Tasks

  • Evaluate backends: Jolt (C++ — would need a C shim), Box2D/box2c (2D), ReactPhysics3D, Mach physics (Zig), or a minimal custom impl. Decide and document.
  • Zig binding/wrapper layer around the chosen library (or the custom module)
  • Collision primitives: sphere, box, capsule (mesh → #34 if heavy)
  • Rigid body dynamics with configurable gravity; integrate the fixed-timestep loop
  • Collision detection + response (restitution/friction basics)
  • Wire RigidBodyComponent + ColliderComponent into the ECS; sync transforms both ways
  • Document performance characteristics and limitations

Acceptance Criteria (Phase 1)

  • Rigid bodies fall under gravity and collide/rest on static colliders.
  • Sphere/box/capsule colliders work and integrate with the component system.
  • No C++ runtime dependency leaks into the engine (C ABI only).

Related

Edited by Bruno Massa