Groom Properties and Settings

A list of all settings and properties relevant to hair rendering and simulation with Groom Assets.

This page contains a 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.

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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 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.

Hair Length Scale

When enabled, this allows scaling the length of the hair.

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.

Use Cards

When enabled, this option forces the groom to use cards/meshes geometry instead of strands.

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.

Simulation

Physics Asset

The Physics Asset to be used for this groom when physics simulation is enabled.

Groom Asset

Imported alembic .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.

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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

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.

Frame Start

The starting index to start sampling the animation from.

Frame End

The ending index to stop sampling the animation at.

Skip Empty Frames at Start of Groom Animation

When enabled, skips empty (pre-roll) frames and starts importing at the frame which actually contains data.

Import Groom Asset

Import, or re-import, the Groom Asset from this file.

Preview

Group Name

The name given to the hair group.

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.

Has Precomputed Weights

This defines whether to use the precomputed weights.

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.

Groom Binding Options

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.

Binding Asset Details

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.