Skip to content

Setting up your mesh for cloth simulation

Havok uses vertex-based cloth simulation, which is what this workflow supports. The simulation is physically accurate, but for performance reasons self-collision is not supported.

Selection Sets / UV Indices

These are vertex selections used to define different behavior zones. Common usage includes:

  • Simulated vertices
  • Fixed vertices
  • Display-only vertices
  • Collision or other constraint groups

To create them:

  1. Select the mesh
  2. Enter Edit Mode
  3. Select the desired vertices
  4. Fill in the Section Name
  5. Press Save UV Indices

particle selection

This will create an entry in:

  • blend_path/export_data/selectionsets/uv_indices.json, or
  • optional_export_path/selectionsets/uv_indices.json

Vertex Selection Groups

Vertex groups are float-based selections used when non-uniform values are required.

To export a vertex group:

  • Create a vertex group on the mesh
  • Set Min Export Value and Max Export Value
  • Select the Weight Group to export
  • Choose a Weight Type

Available weight types:

  • Distance Used for distance constraints or collision radii.
  • Float Used for modifiers.

  • Angle Used for angle-based modifiers.

  • Press a Export Vertex Group(UV Oder)

vertex group exports

The data will be saved to:

  • blend_path/export_data/floatchannels/weight_groups.json, or
  • optional_export_path/floatchannels/weight_groups.json

Collidables

Because cloth meshes move dynamically, precise control over their position is difficult. Collidable shapes are used to restrict or guide movement. The following collidable shapes are available:

  • Capsule
  • Sphere
  • Plane
  • Convex Geometry
  • Convex Heightfield

all types of colision

Notes on Collidables

  • Collidable objects use the prefix collision_<type> so the addon can identify and skip them during processing.
  • They often include a bone name prefix to assign the collidable to a specific bone.
  • Collidables do not need to be parented to the armature and should remain disconnected.

Creating and Assigning Collidables

  • Select a mesh or collidable object shape type you want to change
  • Choose a Collision Type
  • Assign a bone using the Bone Selector (if needed)
  • Press Set Collision to convert the mesh into the selected collision shape

Assigning Collidable type

If the object is already a collidable, it will be updated except a Bone Selector if already set.

When selecting an armature, a Place Collidable button appears:

  • Select one bone in Edit/Pose mode → create a sphere
  • Select two bones in Edit/Pose mode → create a capsule

create sphere

create capsule

Capsule Resizing

When a capsule collidable mesh is selected, additional resize options will appear.

Capsules can be resized using the following control points:

  • Bottom
  • Middle
  • Top

To resize the capsule:

  1. Toggle the desired controls (Bottom, Middle, and/or Top)
  2. Press Resize Capsule to apply the changes

resize capsule

If the capsule's size choses is uneven, the collidable effectively becomes a Tapered Capsule.

Note

Tapered Capsules are not supported by the addon. For proper functionality, it is recommended to convert the collidable to Convex Geometry.