Collision detection

Collision Detection


  • Contains all the physics data on a single asset (e.g. static mesh)

  • Done so that all BodyInstance references can share the physics data/config and not dupe tris everywhere

  • Contains FKAggregateGeom that has simplified collision representation of asset

  • Typically assets implement GetBodySetup function that's used in physics state creation


  • Blocking will naturally occur between two objects set to block

  • Hit events wont trigger unless Simulation Generates Hit Events is set

  • Simulation Generates Hit events doesn't need to be set on both

  • Overlap + Generate Overlap events must both be set for overlap events

  • Interaction between two objects is min of the flags of both actors. Ex:

  • Block + block = block

  • [Block + sim generates hit events] + block = Hit Event on 1st actor + block

  • [overlap+ disabled generate overlapevents] + block = nothing

  • [overlap + generate overlap events] + block = overlap event on 1st actor

  • After first blocking collision, collision system stops looking for collisions


  • Not recommended for object to have generate hit events and overlap events

UE Physics has an async scene + sync scene based on PhysX

  • Async means physics computation results can be reported at later frames

  • Sync means it runs before all UE4 sim code

  • No interdependency calculation between the two

Thread & Sample showing how to update collision at runtime:

Turn On Drawing For Traces/Geometry Sweeps

  • World->DebugDrawTraceTag

  • DrawGeomSweeps

  • DrawGeomOverlaps

There's a Collision Analyzer Tool for debugging Developer Tools->Collision Analyzer