kimbatt / unity-deterministic-physics Goto Github PK

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

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unity unity3d physics physics-simulation physics-engine deterministic

unity-deterministic-physics's Introduction

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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unity-deterministic-physics's Issues

How is this different from the Unity DOTS Physics?

Hi there,

You reference the Units DOTS Physics package in your readme, which claims to be deterministic in its description.

Is the difference here that the Unity DOTS Physics package is only deterministic on the same platform/processor, while this project is deterministic across platforms/processors?

Looks like a cool project!

rollback?

Is it possible to roll back the physics engine to an earlier state with collisions?

Can I use JobHandle in the OnUpdate() function?

Execute ExampleScene, all objects will penetrate the ground!

2D support

Hi,

Can you add support for 2D physics + a 2D example? Thanks!

Hi, Is it possible to release the auto generation unity code tool?

Hi, Is it possible to release the auto generation unity code tool?
xxx.gen
//------------------------------------------------------------------------------
//
// This code was generated by a tool.
//
// Changes to this file may cause incorrect behavior and will be lost if
// the code is regenerated.
//
//------------------------------------------------------------------------------

sfloat values like Translation doesn't show in the inspector?

WebGL Builds are Laggy

Not sure why but webgl builds are pretty laggy.

CollisionWorld.CastCollider doesn't work well!

Editor Authoring functionality missing

First of all I'd like to thank you @Kimbatt for sharing this project. So far it has worked great.

Unity DOTS physics has editor authoring components with the included Unity.Physics.Editor & Unity.Physics.Hybrid (not entirely sure if both are required). With Unity.Physics it is possible to design gameobjects in the editor and use those in the code through subscenes and entity prefabs, but the authoring components are not compatible with this project. At the moment including Unity.Physics.Editor & Unity.Physics.Hybrid gives a ton of errors. I think this project would be complete with the authoring functionality.

Physics quite unstable

I tried playing around for few days with these packages, sadly I can confirm it is far from production ready.

Cylinder/Mesh colliders are very unstable. Also tried the same setup with float version and issues was gone.

Frictions are quite off, as objects loses the force almost 2x faster than in float version.

sfloat:

float:

P.S. Yes the scenarios here shown are not exact the same for comparison. But it is quite obvious then u play around in the scene and in float version everything slides completely differently.

In any case, it is cool package modification and nice attempt for deterministic physics. However, if you dont plan using only boxes and sphere likes in example, you wont find this package doing what you want.

Translation component (and likely other transform components) doesn't affect position of object

Hi,

The UnityS.Transforms.Translation component, which is made to be a soft float equivalent to the Unity.Transforms.Translation component, doesn't affect the actual position of an object. While I'm not 100% certain as to why this is the case, I'm guessing it probably has something to do with Unity using Unity.Transforms.Translation when using Convert To Entity.