Implementing Geometry Collections for Destructible Environments

In this lesson, you will learn how to transform static environment props into dynamic, destructible assets using the Chaos Physics system.

Up until now, our objects have been static meshes—solid, unmoving shells. To create destructible environments, we move away from UStaticMesh components and instead utilize Geometry Collections. A Geometry Collection is a specialized asset type that treats a 3D model not as a single solid volume, but as a cluster of individual "fracture pieces" held together by a data-driven internal structure.

The Conversion Workflow

To begin, you must enable the ChaosEditor plugin. Once active, right-click any static mesh in your Content Browser and select Create Geometry Collection. This initiates the conversion process, which allows you to define how the object breaks. You will be introduced to the Fracture Editor, where you select a "Fracture Method"—such as Uniform or Radial—to slice your mesh into smaller, physical chunks.

Enabling Real-Time Physics

Once converted, the object is no longer governed solely by standard rigid body physics. Instead, it interacts with a Chaos Physics Solver. You must place a GeometryCollectionActor into your level; this actor serves as the anchor point for the physics simulation.

To trigger a collapse based on an impact force, you rely on the Field System. By applying a Radial Falloff or Box Falloff field, you can send "damage" signals to the collection. When an input action (like a projectile firing) overlaps with these fields, the internal bonds between the geometry pieces are broken:

// Logic for applying an impulse to a Geometry Collection at the hit location
void ADestructibleActor::TriggerFracture(FVector HitLocation, float ImpulseStrength)
{
    // The Geometry Collection interprets the impact to fracture its bonds
    GeometryCollectionComponent->ApplyPhysicsField(
        EFieldPhysicsType::Field_ExternalClusterStrain, 
        ImpulseStrength, 
        HitLocation
    );
}

By manipulating these fracture bonds, you can transition a wall from a solid, static obstacle into a crumbling pile of debris the moment an external force threshold is exceeded.

Key Takeaway: Geometry Collections transform rigid static meshes into clusters of breakable shards, allowing you to orchestrate structural collapses by triggering physics-based forces against their internal connection data.