Verlet Transform Tree

A simulation structure for animating hierarchical transforms using Verlet integration. Typically used for tails, ropes, chains, or foliage where child transforms follow dynamic, physics-based motion.

The VerletTransformTree defines and simulates a single transform hierarchy using Verlet physics. It handles node registration, per-frame simulation updates, and optional collision resolution based on settings curves. Each node retains a reference to its transform and original pose for positional and rotational constraints.

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Public Fields

Root

public Transform root;

The root transform of the simulated hierarchy. All children (excluding those in ignoreList) will be registered as nodes.

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Settings

public VerletTransformTreeSettings settings;

Reference to a VerletTransformTreeSettings asset that defines spring, damping, angle limits, drag, and collision curves based on depth in the hierarchy.

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Ignore List

public List<Transform> ignoreList = new List<Transform>();

Any transforms to exclude from simulation. Useful for skipping specific branches of the hierarchy or static bone references.

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Nodes

public List<VerletTransformNode> nodes = new List<VerletTransformNode>();

The list of simulated nodes in the hierarchy. Each node stores initial transform data and current simulation state.

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Show Debug

public bool showDebug = false;

If enabled, node data and wire representations (capsules, links) will be drawn in the Scene view.

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Public Methods

Register Nodes

[ContextMenu("Register Nodes")]
public void RegisterNodes()

Scans the transform hierarchy starting from root and populates the nodes list. Excludes any transforms in ignoreList.

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Add Force

public void AddForce(Vector3 force)

Applies a global directional force to all nodes in the hierarchy.

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Add Force at Position

public void AddForceAtPosition(float forceMagnitude, Vector3 position)

Applies a radial force from a given world position, diminishing by distance. Useful for explosions or impacts.

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Clear Forces

public void ClearForces()

Clears accumulated external forces from all nodes.

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Reinitialise

public void Reinitialise()

Resets all nodes to their original transform state and clears accumulated simulation data. Typically used after editing hierarchy structure in-editor.

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Example Usage

Basic Setup

Attach a VerletTransformTree component to a GameObject and assign the root transform (e.g. a bone or empty parent).

Assign a VerletTransformTreeSettings asset to configure spring behaviour.

Optionally use the context menu "Register Nodes" to initialise the node hierarchy.

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Runtime Force Application

public class TailWhip : MonoBehaviour
{
    public VerletTransformTree tree;

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            tree.AddForce(Vector3.right * 5f);
        }
    }
}

This applies a one-time directional force to all nodes in the tree.