Hair Rendering and Simulation Settings Reference

A list of settings and properties relevant to hair rendering and simulation.

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This page contains reference to settings available for different Components and Actors that use Hair for rendering and simulation in Unreal Engine 4 (UE4).

Groom Actor

The following properties are available from the Groom component's Details panel.

GroomActorSettings.png

Property

Description

Materials

Element [N]

Assign your Hair Material to this Asset slot.

Groom

Groom Asset

Hair strand Asset used for rendering.

Bind Groom to Skeletal Mesh

When activated, the hair groom will be attached and skinned onto the mesh if the Groom Component is a child of a Skeletal Mesh/Skinned component. It requires the following project settings: Compute Skin Cache enabled and Tick Animation on Skeletal Mesh init disabled.

Groom Groups Desc

Groom's group information:

  • Hair Count: The number of hairs within this hair group.

  • Guide Count: The number of simulation guides within this hair group.

  • Hair Width: Override the hair width (in centimeters).

  • 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.

Groom Asset

The following properties are available in the Groom Asset that is created in the Content Browser when importing an Alembic (*.abc) file that contains a hair groom.

Groom_AssetProperties.png

Property

Description

Hair Groups

Group ID

The group ID assigned to this imported hair groom.

Curve Count

The number of curves contained in the imported Groom file.

Guide Count

The number of guides contained in the imported Groom file.

Auto-Generated Guides

This is checked when Override Guides is enabled during import of a Groom file.

Material

Assign a default Material to be used by this Groom Asset.

Build Settings

Hair to Guide Density

Density factor for converting hair into guide curve if no guides are provided.

File Path

Source File

The drive file path to the source Groom file that was imported.

Groom Import Options

The following import options are available when importing an Alembic (*.abc) file that contains a hair groom.

GroomImportOptions.png

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.

Build Settings

Override Guides

Overrides imported guides with generated ones.

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 which guides affect a given hair strand.

Use Unique Guide

Forces a hair strand to be affected by a unique guide.

Niagara Groom Asset System

The following properties are custom parameters set up in the Niagara GroomAssetSystem that controls the hair physics when assigned to a Groom component.

NiagaraOverrideParameters.png

Use the Niagara System selection box to assign the GroomAssetSystem. If you do not see it, enable Show Plugin Content from the dropdown's View Options.

Property

Description

Default Value

Override Parameters

AirDensity

Default hair density in g/cm3.

0.001

AirDrag

Coefficient between 0 and 1 to describe how much the groom is going ot be dragged into the air.

1.0

AirVelocity

Uniform air velocity in cm/s that is used to drag the groom.

0,0,0

BendDamping

Rayleigh damping of the bending constraint. This value must be between 0 and 1.

0.001

BendScale

Describes how much the BendStiffness will be scaled from the root to tip. For example, with a value of 0.1, the tip bend stiffness is equal to 0.1 * root bend stiffness.

0.1

BendStiffness

This describes how much the groom will maintain its rest shape. The value is in megapascal (MPa).

0.01

GravityVector

Vector of the gravity acceleration that will be applied onto the groom in cm/s2.

0.0,0.0,-981.0

KineticFriction

Coefficient between 0 and 1 that will set the kinetic friction.

0.1

NumIterations

Number of iterations used for the constraints iterative solver (XPBD)

10

ProjectBend

Enables the constraint projection for the bend constraint.

Disabled

ProjectCollision

Enables the constraint projection for the collision constraint.

Enabled

ProjectStretch

Enables the constraint projection for the stretch constraint.

Disabled

RootThickness

Thickness of the root measured in centimeters (cm). This property will be used by simulation to compute the mass and inertia.

0.1

SolverFps

Sets the sampling rate of the solver, such as, how many times the solver is going to be called per-second.

60

StaticFriction

Coefficient between 0 and 1 that sets dry friction.

0.1

StrandsDensity

Density of the groom strands in g/cm3.

1.0

StrandsSmoothing

A value between 0 (original curve) and 1 (straight line) controls how much the incoming guide curve is smoothed. This smoothing could help the solver to converge.

0.1

StrandsViscosity

Sets how the strands are influencing each other.

1.0

StretchDamping

Rayleigh damping of the stretching constraint. The value must be between 0 and 1.

0.001

StretchScale

Describes how much the StretchStiffness will be scaled from root to tip. For example, with a value of 0.1, the tip stretch stiffness is equal to 0.1 * root stretch stiffness.

1.0

StretchStiffness

This value describes how much the groom will keep its rest length. The value is in megapascal (MPa).

1.0

SubSteps

Number of substeps that will be applied to the dt given by the parameter SolverFps.

TipThickness

Thickness of the tip measured in centimeters (cm). This property is used by simulation to compute the mass and inertia.

0.1

Niagara

Niagara System Asset

Assignment slot for an available Niagara Particle System Asset. For Hair, this should be the GroomAssetSystem that is assigned.

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