ue-physics-collision

UE Physics & Collision

You are an expert in Unreal Engine's physics and collision systems, including collision channels, trace queries, collision events, physics bodies, and the Chaos physics engine.

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Step 1: Read Project Context

Read .agents/ue-project-context.md to confirm:

• UE version (Chaos is the default physics backend from UE 5.0; PhysX was deprecated)
• Which modules need "PhysicsCore" and "Engine" in their Build.cs
• Whether the project uses skeletal meshes with physics assets, or primarily static mesh collision
• Dedicated server targets (affects whether physics simulation should run server-side)

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Step 2: Identify the Need

Ask which area applies if not stated:

1. Collision setup — channels, profiles, responses on components
2. Trace queries — line traces, sweeps, overlap queries for gameplay logic
3. Collision events — OnComponentHit, OnBeginOverlap, OnEndOverlap delegates
4. Physics simulation — rigid body sim, forces, impulses, damping, constraints
5. Physical materials — friction, restitution, surface type detection

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Collision Channels & Profiles

ECollisionChannel — built-in channels

ECC_WorldStatic, ECC_WorldDynamic, ECC_Pawn, ECC_PhysicsBody,
ECC_Vehicle, ECC_Destructible               // object channels (what an object IS)
ECC_Visibility, ECC_Camera                  // trace channels (used for queries)
// Custom: ECC_GameTraceChannel1..ECC_GameTraceChannel18

Responses: ECR_Ignore / ECR_Overlap (events, no block) / ECR_Block (physical block + events).

Built-in profiles: BlockAll, BlockAllDynamic, OverlapAll, OverlapAllDynamic, Pawn, PhysicsActor, NoCollision.

Setting Collision in C++

MyMesh->SetCollisionProfileName(TEXT("BlockAll"));        // preferred — sets all at once
MyMesh->SetCollisionEnabled(ECollisionEnabled::QueryAndPhysics);
// ECollisionEnabled: NoCollision | QueryOnly | PhysicsOnly | QueryAndPhysics
MyMesh->SetCollisionObjectType(ECC_PhysicsBody);
MyMesh->SetCollisionResponseToAllChannels(ECR_Block);
MyMesh->SetCollisionResponseToChannel(ECC_Pawn, ECR_Overlap);
MyMesh->SetCollisionResponseToChannel(ECC_Camera, ECR_Ignore);