Integrating Anchor Fields for Structural Integrity

In this lesson, you will learn how to use Anchor Fields to designate specific parts of a Geometry Collection as "unbreakable," ensuring your buildings don't crumble like sandcastles the moment they take damage.

The Problem: Total Collapse

When you fracture a mesh in Chaos, the engine treats every piece as an independent dynamic object subject to gravity. If you destroy a wall at the base, the entire structure will realistically—but often frustratingly—collapse instantly. In game design, we usually want specific sections (like foundations or load-bearing pillars) to remain anchored to the world, providing a sense of structural integrity.

Integrating Anchor Fields

An Anchor Field acts as a constraint that effectively "pins" pieces of your Geometry Collection to their original transform, overriding the default physics simulation.

To implement this, you use a Field System Actor. Instead of using a Radial Force to push objects, you use a Master Field with an Anchor node.

1. Create a Field System Actor: Place it in your level and position it where you want the "support" to be (e.g., the foundation of a building).
2. Setup the Anchor: Inside your Field System Actor, set the evaluation type to Field_EFieldPhysicsType::Field_PhysicsType_ExternalClusterStrain or apply the Anchor field directly. This forces the engine to ignore gravity and impact forces for any pieces currently intersecting that field’s volume.
3. Logic Implementation: You can trigger this via Blueprints using the Apply Physics Field node.

// Conceptual flow for applying an anchor field
void AStructuralSupport::InitializeAnchor() {
    // We define the field region to be "static"
    // Any chunk inside this bounds will resist structural failure
    FieldSystemComponent->ApplyPhysicsField(
        true, 
        Field_PhysicsType_ExternalClusterStrain, 
        nullptr, 
        AnchorFieldNode
    );
}

Why Use This?

By applying an Anchor Field to the base of your Geometry Collections, you create a "safe zone." Even if you blast the upper floors with a Radial Force Field, the bottom floor will remain locked in space, allowing players to destroy a tower while leaving the foundation intact. This technique is essential for balancing visual destruction with gameplay requirements for stable environments.

Key Takeaway: Anchor Fields override physics simulations for selected geometry clusters, allowing you to selectively freeze parts of a mesh in place to preserve essential structural supports.