In this lesson, you will learn how to use radial falloff fields to trigger localized, procedural fractures on Geometry Collections when objects impact a surface.
The Concept of Falloff Fields
When you convert a mesh into a Geometry Collection, it stays static until a force acts upon it. While a standard explosion pushes everything, a Radial Falloff Field allows you to dictate exactly how that force propagates.
A radial field defines a sphere of influence: the center of the sphere has maximum impact, and the influence tapers off (falls off) toward the outer edge. By connecting this to a Field System Actor, you can trigger a fracture only where your gameplay event occurs—like a player slamming their fist on a table or a projectile hitting a wall.
Implementation Logic
To trigger this, you don't just apply force; you apply a Radial Intrinsic Pull or Radial Vector field. The "Falloff" component is the key, as it determines the curve of the force. If you set the Falloff to Linear, the force decreases steadily as you move away from the impact point.
You typically set this up within your Blueprint logic when an overlap or hit is detected:
// Logic flow for triggering a fracture
void AImpactActor::TriggerFracture(FVector ImpactLocation, float Radius)
{
// 1. Create a Radial Falloff Field component
// 2. Set the Radius and Falloff type to Linear
// 3. Pass this field to the Geometry Collection's Field System
// 4. The field interprets the magnitude based on the Distance from center
}
By keeping the radius small and the magnitude high, you create a "crunch" effect, where only the immediate area around the collision fractures, rather than the entire object shattering at once. This adds a layer of realism to your destructible environments by ensuring that the scale of the damage matches the scale of the event.
Key Takeaway: Radial falloff fields allow you to transition from simple static objects to dynamic, shattered ruins by mapping the intensity of destruction to the precise distance from an impact point.