Setting Up Bindings for Grooms

Groom Binding assets are used to attach and skin a Groom component to a Skeletal Mesh component. No binding is needed if a groom asset only needs to be “rigidly” attached to a skeletal mesh.

Creating a Binding Asset

To create a Binding asset:

1. Locate a Groom asset in the Content Browser.
2. Right-click on the groom and select Create Binding from the context menu.

3. In the Groom Binding Options dialog window, set the following:

   

   • Set Groom Binding Type to Skeletal Mesh or Geometry Cache to bind the groom to.

     Selecting Geometry Cache as the Groom Binding Type requires the Geometry Cache plugin to be enabled.

   • Set Target Skeletal Mesh / Target Geometry Cache to select which skeletal mesh or geometry cache asset this groom should be bound to. You must select a skeletal mesh or geometry cache to create a binding asset.

Advanced Options for Creating a Binding Asset

The Groom Binding Options dialog contains some advanced options you can use when creating a binding asset:

• Use Num Interpolation Points to define the number of samples used for the hair global interpolation, which is optionally enabled within the Groom Asset Editor under the Interpolation panel with the setting RBF Interpolation under the Hair Interpolation section. Global interpolation preserves the original groom shape under large skeletal mesh deformations. Using more samples means more accurate deformation but also implies additional cost. In general, a 100 samples or less should be good enough.
• Source Skeletal Mesh optionally defines the mesh on which the groom was authored on. The mesh could be different from the Target Skeletal Mesh assigned, and the topology could also be different. The system assumes both the Source and Target meshes share the same UV mapping to transfer the hair curves and positions. The Matching Section constrains the transfer to use only a particular mesh section.

Setup

To use a groom binding asset to bind a groom to a skinned mesh:

1. Create a Groom component and make it a child component of a skeletal mesh. You can do this directly on a Skeletal Mesh in a level or in a Blueprint.

   A Groom component on a level actor.	A Groom component in a Blueprint.

2. With the Groom component selected, perform the following actions in the Details panel:

   • Assign a groom asset to the Groom Asset assignment slot.
   • Assign a groom binding asset to the Binding Asset assignment slot.

Your groom should look attached similarly to how the one pictured below is:

The binding data is only used if the current level of detail (LOD) Binding Type is set to Skinning. This can be set up separately for each LOD in the Groom Asset Editor under the LOD panel settings. You can verify the current active binding type in the level by selecting Lit > Instances in the viewport menus and visualizing the Binding Type for each.

Click image for full size.

Previewing Groom Bindings in Groom Asset Editor

The Binding panel in the Groom Asset Editor is where you'll manage any binding asset assigned to this groom. It lists all the groom binding assets compatible with the current groom asset.

You can use the Eye icon below the binding asset assignment slot to preview the binding asset within the preview window.

You can use the animation assignment slot above the preview window to select an available animation to preview the hair deformation for the current groom. Use the play and stop buttons to start and stop the animation in the preview window.

You can visualize a groom's Root data in a level by selecting Lit > Groom > Root Bindings. The root binding data for each rendered strand is shown by a colored white line at the root of the hair, along with the corresponding triangle on which the root is bound.

Groom Binding Properties

Groom Binding Options Properties

The following properties are found in the Groom Binding Options dialog when creating a groom binding asset:

Groom Binding Asset Editor Properties

The following properties are found in the Groom Asset Editor when opening a groom asset:

Groom Asset Editor Binding Properties

The following properties are found in the Groom Asset Editor under the LOD panel: