All content in this course uses:

Test the Hair Simulation

In this tutorial, you will use the Hair Simulation System to create and customize hair assets.  

SampleHair.zip

The sample scene provides you with a basic setup of a procedural groom (in the form of a debug-colored curtain) and some primitives for collision demonstration. 

In this tutorial, you will explore the Hair System and learn how to create and customize hair assets.  

Overview

Follow these instructions to import the sample assets and scenes for this project:

. In the Demo Team Hair System package, select the 

button to download assets and sample scenes.

. Locate the sample content in your Project directory at 

Assets\Samples\Demo Team Hair System\0.9.0-exp.1\Minimal Hair Sample

Import the minimal hair sample scene

 directory. Open the sample scene for the 

 your project uses.  The sample scene provides you with a basic setup of a procedural groom (in the form of a debug-colored curtain) and some primitives for collision demonstration. 

Feel free to explore the system by changing the hair asset's parameters (located in 

 in your project) and the hair instance (in 

). Or why not make a brush out of the curtain? Select 

: If you want your hair simulation to continuously update in the Scene view when you are not in Play mode, select the 

Explore the hair sample scenes

The Hair System makes it possible for you to easily create 

, either from grooms you import from external 3D modeling software (with the 

 file format for curve data), or through simple procedural generation tools — to scatter hairs on a mesh or other primitive, or use a custom generator, for example.

Shape strands with simple parameters like length and curl.

Plug in your own generators for custom placement.

Import grooms from 3D modeling software, like Weta Wig, Houdini, Maya Xgen, etc., through the Alembic file format (.abc) with the option to resample curves with an adjustable particle count along each strand. 

If you need a sample Alembic file, you may download this 

hair asset, right-click in the Project window and select 

The hair asset

 controls the hair asset and its simulation parameters, such as system and strand settings (for example, configurable constraints or level of detail (LOD)) and the hair instance volume settings (including the hair instance volume debug settings). You can assign multiple hair assets to one instance, such as main groom, fly-aways, or baby hairs. This division of groom parts could be relevant for characters with human hair, for example.

Follow these instructions to create a hair instance:

Add a Hair Instance component to the empty GameObject. 

property of the Hair Instance Inspector. 

: In order to expose all Hair Instance parameters, select the 

 (⋮) menu and then expand each subsection as the screenshots below illustrate. 

The hair instance

Follow these instructions to create a procedural groom:

 to rebuild your asset after you adjust strand settings so you can understand the effect of properties such as 

button to have Unity automatically rebuild your asset each time you change a parameter value.

Procedural groom on a user-specified mesh

You can build clusters and level of detail (LOD) chains automatically based on spatial relationships. The Hair System supports root, strand, and simplified strand-level clusters.

You can also automatically generate and easily adjust LODs on a hair instance and seamlessly blend between LODs while the simulation is running.

A first look at levels of detail

The hair instance comes with a variety of settings options. Below we explain some of the settings to help you determine how to use them to customize your project to your specifications.  

There are these strand-rendering options:

: Renders hair strands with a line topology. This implies that the hair width is always 1 pixel.

: Renders the hair strands as quads, each made of 2 triangles.

: Renders the hair strands using HDRP's software line renderer. Only available if your project uses the HDRP pipeline version 15.

The hair simulation can run at 30, 60 or 120Hz. Higher values produce more stable and precise results but require more system resources and potentially cause performance slowdowns. 

 determine the number of simulation steps executed per visual update in the Unity game loop.

 This outputs the hair simulation result to a staging buffer before rendering, which allows for tessellation prior to rendering, as well as  precise motion vectors. There are two 

: Increase this value above 0 to smooth strand curves, although this reduces performance. 

 precision is the fastest, most memory-efficient option to provide reasonable quality, but it can also produce artifacts if it is insufficiently precise.

 method is the preferred option, since it converges faster than the 

 control the behavior of the simulated hair strands. 

 is the number of times the hair simulation evaluates the 

 frequency interval. The higher you set this value, the more precise Unity's representation of the 

All physics simulations work best with small and constant time steps. Adjusting the 

 property allows the user to divide regular time steps into smaller intervals. A higher 

 value produces higher precision, more stable results, but also requires more system resources. Currently, the difference between a step and a substep is that the simulation volume and boundary data is only rebuilt per step, and interpolated per substep. 

These properties provide linear and angular damping to subtract a fraction of the hair strands' velocity over an adjustable time interval. They include a scaling factor for gravity, which allows for negative gravity effects.

Customize the simulation settings for your groom: Parameter Adjustment

: Enables blending in global position (the reference pose prior to simulation) over a specific time interval. 

 behaves similarly, but for segment rotation.

 from the root to the tip of a strand. The 

determine where and for how long to fade the effect, normalized to the longest strand in each group.

The hair system supports sphere, cube, capsule, torus, and discrete SDF colliders. 

Hair instance settings

Follow these instructions to configure a hair instance to respect boundaries (colliders): 

 settings of the hair instance that you want to respect boundaries (colliders). 

 option to automatically recognize physics colliders (for example, spheres, cubes, capsules). 

 to set the hair instance to automatically pick up 

 colliders. This allows Unity to identify regular colliders or triggers that have a Hair Boundary component. The Hair Boundary component provides the primitive definition to the hair system. 

Unity Version 2021.2