UnrealJolt

Plugin that brings Jolt Physics into unreal engine 5

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Getting Started

Some things to consider before using this

• This is a bolt on integration and not a replacement for the existing chaos physics solver.
• You should only need this if you specifically want some kind of behaviour that's not available in chaos.
• Deterministic physics, multicore processing of many bodies could make the case.
• Multicore processing it not yet implemented properly using Unreal's own thread pool system.
• The implementation of this plugin while is generic (somewhat), is still tied to something I am developing on the side. Just keep in mind that all features of UE might not be integrated, you might have to do it yourself. (Drop a PR if you do :) )
• There are possibilities of breaking changes, until 1.0.0 at least. (will try to avoid)

Requirements

• Unreal engine 5 (mostly tested on 5.6.0, should work on older versions)

Installation

• Clone (git clone --recursive git@github.com:Yadhu-S/UnrealJolt.git) or download into the Plugins folder (<project>/Plugins or Engine/Plugins)
• Take a look inside UnrealJoltLibrary.Build.cs to see the user defines, modify what you need, or leave defaults. Check the available defines here
• Compile project
• Make sure UnrealJolt is enabled in "Plugins"
• Use actor-tag and tag dynamic objects with jolt-dynamic (make sure that the object is movable) and static objects with jolt-static

Configuration

• Plugins->Jolt in your project settings.
• Check the defaults, and change if required.
• Debug rendering is slow, especially when visualizing large heightmaps. Drawing all those triangles. (Need to look into drawing triangles only once for static objects )

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Features

UJoltSkeletalMeshComponent

• UJoltSkeletalMeshComponent extends USkeletalMeshComponent to add jolt specific functionality (Browse JoltSkeletalMeshComponent.h to see the available functions)
• Modify the physics asset as required through the editor
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  • Compound shapes are also supported
• Adjust the options as required
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  • Adjust the "Visual Offset" to align the visual mesh with the physics body

Heightmaps

• Landscapes and LandscapeSplines are cooked automatically when you Play in Editor.
  • This may be a chore if you work with many levels, playing a level at least one time in editor (will work on it).
• A JoltData directory is always generated during cooking and must be included when packaging your project.

• ⚠️ Function for reading landscape spline data is not exposed by default in UE

✅ Enabling Landscape Spline Cooking

1. Modify Engine/Source/Runtime/Landscape/Classes/LandscapeSplineSegment.h and add LANDSCAPE_API to the GetLocalMeshComponents() declaration to fix link errors
2. In UnrealJolt/Source/UnrealJolt/UnrealJolt.Build.cs, uncomment: PublicDefinitions.Add("JOLT_PLUGIN_LANDSCAPE_API_MODIFIED");

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Deterministic simulation

To ensure deterministic simulation with Jolt Physics across platforms, follow the official guidelines. Use Jolt’s math and utility functions (Sin, Cos, QuickSort, BinaryHeapPush/Pop, Hash) instead of STL or platform-dependent ones, and always keep API calls (body/constraint creation, updates) in the same order.

For builds:

• On Windows (MSVC), add FPSemantics = FPSemanticsMode.Precise; to <ProjectName>Target.cs and <ProjectName>Editor.Target.cs.
• On Linux (Clang), add AdditionalCompilerArguments += " -ffp-model=precise -ffp-contract=off"; to the same files.

Because these options differ from Unreal defaults (LinuxToolChain.cs, VCToolChain.cs), create a custom build config or apply the changes consistently across both game and editor builds by modifying:
UnrealClient.Target.cs, UnrealEditor.Target.cs, UnrealGame.Target.cs, and UnrealServer.Target.cs.

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Contributing

Found this project useful? Awesome!

If you’ve added a feature, fixed a bug, or improved something that isn’t here yet—feel free to open a PR!

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Credits

• Jorrit Rouwe for making jolt
• Andrea Catania for the video series on YouTube