Custom jobs

Little Physics exposes three public system groups where you can plug in ECS systems, plus four job interfaces that schedule Burst-friendly work over native physics buffers. Together they let you read and modify simulation state at import, mid-step, and export without fighting the internal pipeline.

When to use what

Goal	Hook	Recommended API
Override ECS data before it enters native memory	Import workflow — before internal import	ECS components
Patch BodiesList or maps after import	Import workflow — after internal import	Native structures + PhysicsJobHandle
Apply forces, custom collision response, gameplay	Inside the pipeline — LittlePhysicsUserSystemGroup	Package job interfaces
Read native results before write-back	Export workflow — before internal export	Native structures
Sync to rendering, networking, or destroy entities	Export workflow — after internal export	ECS components

Prefer the package job interfaces inside the fixed-step loop. They iterate the correct buffers, respect ActiveBodiesCount, and chain PhysicsJobHandle through ScheduleAndChain. For raw IJob / IJobParallelFor work, combine dependencies manually — see Custom job interfaces.

Job interfaces

All four interfaces run in LittlePhysicsUserSystemGroup unless noted. Three are parallel over active bodies or collision slots; ILineCastJob uses a single helper thread.

Interface	Iterates	Parallel
IBodiesJob	Every active body in BodiesList	Yes
ICollisionJob	Object-to-object collision slots in CollisionDataMap	Yes
ISurfaceJob	Surface contacts in SurfaceCollisionMap	Yes
ILineCastJob	Linecast hits against the spatial map	No (single thread)

Prerequisites

Custom systems should:

1. Gate on PhysicsReadyTag after bootstrap completes.
2. Read simulation buffers from PhysicsStructuresComponent.
3. Chain jobs through SimulationDataComponent.PhysicsJobHandle whenever you touch native memory outside the package interfaces.

Use LittlePhysicsTimeComponent.DeltaTime inside LittlePhysicsUserSystemGroup for the scaled substep delta (respects time scale and substeps).

Samples

The package All Samples import includes working custom-job examples:

Sample scene	System	Interface / group
Scene 4 — Trigger	TriggerAttractionSystem	ICollisionJob.IWriteBodies
Scene 5 — Linecast	LineCastSystem	ILineCastJob.IWriteBody
Scene 5 — Linecast	LineCastInputSystem	LittlePhysicsImportGroup (pre-import input)
Scene 3 — Pachinko	DisappearAtYSystem	LittlePhysicsExportGroup (post-export cleanup)

Related

• Pipeline — full system group hierarchy and execution order
• Physics singleton — native buffers your jobs read and write
• Custom job groups — import, mid-step, and export hook points

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Table of contents

• Custom job groups
• IBodiesJob
• ICollisionJob
• ISurfaceJob
• ILineCastJob
• Custom job interfaces
• Import workflow
• Export workflow
• Inside the pipeline