Groom Properties Reference | Unreal Engine 4.27 Documentation

This page contains reference for properties and settings available for Hair Rendering and Simulation using Groom Assets.

Groom Component

The following properties are available from the Groom component's Details panel when added to a Level as an Actor or when added to a Blueprint.

Property	Description
Groom Group Desc
Hair Width:	Overrides the hair width (in centimeters).
Hair Root Scale	The scale of the hair width at the root.
Hair Tip Scale	The scale of the hair width at the tip.
Hair Clip Length	The normalized hair clip lenght. For instance, at which length the hair will be clipped. 1 means no clipping, and 0 means hairs are fully clipped.
Hair Shadow Density	Controls the hair density to reduce or increase hair count during shadow rendering. It enables you to inrease/decrease the shadowing on hair when the number of strands is not realistic.
Hair Raytracing Radius Scale	Scales the hair geometry radius for ray-tracing effects, such as shadows.
Use Hair Raytracing Geometry	Enables hair geometry to be used with ray tracing features.
LOD Bias	Sets the bias for the selected level of detail (LOD). A value greater than 0 will progressively select lower detailed LODs. This property is used when 'r.HairStrands.Cluster.Culling' is enabled.
Use Stable Rasterization	When enabled, this ensures the hair does not alias. When enabled, groups of hairs might appear thicker. Isolated hair should remain thin.
Scatter Scene Lighting	When enabled, hair is lit with the scene color. It is used for vellus/short hair, like peach fuzz, to bring light from the surrounding surface, like skin.
Materials
Element [N]	Assign your Hair Material to this Asset slot.
Groom
Groom Asset	The Groom Asset to be used for rendering this Actor.
Binding Asset	An optional Binding Asset for binding a groom onto a Skeletal Mesh. If the Binding Asset is not specified, the projection is done at runtime, which implies a large GPU cost at statup time.
Physics Asset	The Physics Asset to be used for this groom when physics simulation is enabled.
Attachment Name	An optional name, where the Groom component should be attached at, when parented to a Skeletal Mesh.
Groom Cache
Groom Cache	The groom animation to playback on this component. It must be compatible with the Groom Asset.
Running	Enable to play back the animation.
Looping	Enable to loop the animation when the elapsed time is past the animation range.
Manual Tick	Enable to play back only through Sequencer.
Elapsed Time	This is a read-only value that shows the time that has elapsed since the start of the animation.

Groom Asset

Imported alebmic (.abc) files create a Groom Asset in the Content Browser. When opened, the Groom Asset Editor enables you to edit properties and settings relevant to the groom.

For more information, see the Groom Asset Editor User Guide .

Groom Import Options

The Groom Import Options are available when importing a Groom Alembic (*.abc) file. Grooms are imported as one of two options: a Groom asset or as an animated Groom Cache.



Groom Import Options	Groom Cache Import Options

Property	Description
Conversion
Rotation	Rotation in Euler angle in degrees to fix up or front axes.
Scale	Scale value to convert file unit into centimeters.
Groom Cache
Import Groom Cache	Import the animated groom detected in this alembic file.
Import Groom Asset	Import the groom detected in this file.
Preview
Group ID	The ID given to the hair strands in this hair group.
Curve Count	The number of hair strands within this hair group.
Guide Count	The number of simulation guides within this hair group.
Preview: Decimation Settings
Curve Decimation	Uniformly reduces the number of hair strands used.
Vertex Decimation	Uniformly reduces the number vertices for each hair strand.
Preview: Interpolation Settings
Override Guides	Replaces the imported guides by selecting a set of strands from the imported groom. The amount of guides depends on the value set by Hair to Guide Density.
Hair to Guide Density	Density factor for converting hair into guide curve if no guides are provided.
Interpolation Quality	Interpolation data quality: Low: Builds interpolation data based on nearest neighbor search. Low quality interpolation data, but fast to build, taking only a few minutes. Medium: Builds interpolation data using curve shape matching search but within a limited spatial range. This is a tradeoff between Low and High in terms of quality and build time, which can take several minutes. High: Builds interpolation data based on curve shape matching search resulting in high quality interpolation data. But it is relatively slow to build, taking several dozen minutes. ]
Interpolation Distance	Interpolation distance metric: Parametric: Builds interpolation data based on curve parametric distance. Root: Builds interpolation data based on distance between guide's root and strand's root. Index: Builds interpolation data based on guide and strands vertex indices.
Randomize Guide	Randomize how guides influence a strand.
Use Unique Guide	Enables whether only a single or multiple guides should influence a strand.

Binding Asset Options

The following properties are available creating or opening an Binding Asset for a given Groom Asset in the Content Browser. Right-click a Groom Asset and choose the Create Binding option from the menu to open these properties.

Property	Description
Build Settings
Groom Binding Type	Sets the type of binding to create a Groom Asset Binding for: Skeletal Mesh or Geometry Cache.
Target Skeletal Mesh	The Skeletal Mesh which the Groom Asset is attached to.
Hair Interpolation
Num Interpolation Points	The number of points used for Radial Basis Function (RBF) interpolation.
Conversion
Source Skeletal Mesh	The Skeletal Mesh on which the groom was originally authored. This is an optional slot, and is only used if the hair binding is done on a different Skeletal Mesh than the one which it has been authored.
Matching Section	The number of points used for the Radial Basis Function (RBF) interpolation.

Binding Asset

After having created a Binding Asset for a Groom, you can open it from the Content Browser to access the following properties.

Property	Description
Build Settings
Groom Binding Type	Sets the type of binding to create a Groom Asset Binding for: Skeletal Mesh or Geometry Cache.
Groom	The Groom Asset that this Binding Asset is attached to.
Source Skeletal Mesh	The Skeletal Mesh on which the groom was originally authored. This is an optional slot, and is only used if the hair binding is done on a different Skeletal Mesh than the one which it has been authored.
Target Skeletal Mesh	The Skeletal Mesh on which the groom is attached to.
Num Interpolation Points	The number of points used for Radial Basis Function (RBF) interpolation.
Matching Section	The number of points used for the Radial Basis Function (RBF) interpolation.
Hair Groups
Curve Count	The number of curves contained in the imported groom file for this binding asset.
Curve LOD	The number of rendered level of detail curves used for this binding asset.
Guide Count	The number of guides contained in the imported groom file used for the binding asset.
Guide LOD	The number of simulation levels of detail used for this binding asset.