In this lesson, you will learn how to structure nested cluster hierarchies to control the sequential breakage of complex destructible objects.
When you create a Geometry Collection using a standard Voronoi fracture, the object shatters into dozens or hundreds of small pieces instantly. This often looks chaotic and unrealistic for large structures like a stone bridge or a concrete pillar. To fix this, we use Cluster Hierarchies, which group smaller fragments into larger "parent" chunks that must break apart before the individual pieces can separate.
Structuring the Hierarchy
Imagine a stone pillar. Instead of every piece being independent, you want the pillar to first crack into three or four large sections (the primary clusters). Only after those sections take additional damage should they break down into smaller rubble.
In the Fracture Mode editor, you handle this through the Cluster tab. The hierarchy is defined by Levels:
- Level 0: The base object (the whole pillar).
- Level 1: The primary clusters (the large sections the pillar splits into first).
- Level 2+: The secondary clusters (smaller pieces that break off the Level 1 chunks).
Configuring the Cluster Level
To enforce this behavior, you must adjust the Damage Threshold settings on the Geometry Collection component. If your primary clusters have a high threshold and your secondary pieces have a low one, the object will appear solid until it receives enough force to break the Level 1 connections.
You can visualize this in the viewport by toggling Show -> Chaos -> Geometry Particles -> Cluster Index. When you fracture, you’ll see the "parent" nodes grouping the "child" nodes. To move an object from a single chunk into a hierarchy, use the Cluster tool to select specific geometry nodes and assign them to a new parent. This ensures that when an impact occurs, the system evaluates the parent cluster's integrity before allowing its children to separate from the main mass.
Key Takeaway: Cluster hierarchies allow you to define a "damage-to-break" sequence, ensuring that large structures collapse into realistic chunks before shattering into finer debris.