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Unity deterministic physics

This is a modified version of Unity DOTS Physics version 0.6.0-preview.3, which supports cross-platform deterministic physics simulation by using soft floats.

Usage

The following packages must be installed:

  • Burst
  • Collections
  • Entities
  • Jobs

You'll need to use the UnityS.Physics and the UnityS.Mathematics namespaces instead of the usual Unity.Physics and Unity.Mathematics.

See Unity Physics manual for documentation.

Notes on determinism

For a deterministic physics simulation:

  • All bodies must be created in the same order every time you create the simulation
  • Bodies must only be modified in a system that is updated in FixedStepSimulationSystemGroup
  • You must not use the result of floating point operations as input for the physics engine
  • Be careful when using hashmaps / hashsets, because iterating over them may be non-deterministic (it depends on the implementation).
  • Check how to use soft floats here.
  • Make sure that your code is also deterministic.

Example

See the ExampleScene scene for an example. After running it, your simulation should look exactly like this:

License

Unity.Physics, Unity.Mathematics, and Unity.Transforms are licensed under the Unity Companion License.

Soft floats is licensed under the MIT License. See https://github.com/Kimbatt/soft-float-starter-pack for more information.

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Cross-platform deterministic physics simulation in Unity, using DOTS physics and soft floats

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