In this lesson, you will learn how to use Field System Actors to create invisible spatial "zones of influence" that dynamically manipulate how Chaos Geometry Collections react to physics in your scene.
The Invisible Hand of Chaos
Up until now, you’ve focused on defining how objects fracture. But how do you trigger those fractures, or add forces like wind or gravity, exactly where you want them without manually updating every mesh? That is the role of the Field System Actor.
Think of a Field System Actor as a "broadcast station" that emits physics rules. Anything inside its radius—a sphere, box, or cylinder—is forced to obey the instructions you define. You aren't applying force to a specific mesh; you are creating a region of space that says, "Anything that enters here gets pushed left" or "Anything inside here must shatter immediately."
Setting Up the Field
To get started, drag a Field System Actor from your Place Actors panel into your level. This actor serves as the hub. You then add "Fields" to it, which function like commands in a list. For example, a Radial Falloff field can define a circular area, and a Strain field can use that volume to tell a nearby destructible wall to shatter.
You can bridge these systems by using the Field System Component on your Geometry Collection to listen for these inputs. If you want a player’s explosion to shatter a wall, you spawn a Field System Actor at the impact point with a Radial Vector field. The Geometry Collection within that radius will react instantly based on the intensity you set.
// Logic flow for activating a field
// 1. Define the shape (e.g., Radial Falloff)
// 2. Define the influence (e.g., Force, Sleep, or Kill)
// 3. Apply to the Field System Actor
// 4. Geometry Collection inside the zone receives the physics state change
By decoupling the action (the field) from the object (the geometry), you keep your physics system performant and modular. You can reuse the same field setup for different objects without re-writing logic for each individual destructible mesh.
Key Takeaway: Field System Actors act as spatial volumes that override local physics behavior, allowing you to manipulate geometry dynamically without modifying the meshes themselves.