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You can set up physics simulations for your grooms by enabling settings within the Groom Asset Editor and the Groom component.
Enabling Physics Simulation on a Groom
To enable Physics simulation for a groom go to the Groom Asset Editor > Physics panel. Enable the checkbox for Enable Simulation.
Once enabled, the groom should now simulate physics. Below is an example of the groom simulation while a character is walking.
Physics Simulation Properties
You can find the simulation properties for grooms in the Groom Asset Editor and on a Groom component.
Groom Asset Editor Simulation Properties
The following simulation settings are found in the Groom Asset Editor under the Physics and LOD panels.
Physics Panel Settings
The following settings are found in the Physics panel:
| Property | Description |
|---|---|
| Solver Settings | |
| Enable Simulation | Enables physics simulation for this groom grouping. |
| Niagara Solver | Select the solver to be used for simulation:
|
| Custom System | Add a custom Niagara system to use when the property Niagara Solver is set to Custom Solver. |
| Sub Steps | The number of sub steps to be done per frame. Solver calls are done at 24 frames per second. |
| Iteration Count | The number of iterations to solve constraints with the XPBD solver. |
| External Forces | |
| Gravity Vector | The acceleration vector measured in cm/s2 to be used for gravity. |
| Air Drag | The coefficient between 0 and 1 to be used for air drag. |
| Air Velocity | The velocity of the surrounding air measured in cm/s. |
| Bend Constraint | |
| Solve Bend | Enables solving of the bend constraint during the XPBD loop. |
| Project Bend | Enables the projection of the bend constraint after the XPBD loop. |
| Bend Damping | Damping applied for the bend constraint using a value between 0 and 1. |
| Bend Stiffness | The stiffness for the bend constraint in GPa. |
| Bend Stiffness Scale | This curve determines how much the bend stiffness is scaled along each strand. The x-axis range is 0,1, where 0 maps to the root and 1 to the tip of the strand. |
| Stretch Constraint | |
| Solve Stretch | Enables solving of the stretch constraint during the XPBD loop. |
| Project Stretch | Enables the projection of the stretch constraint after the XPBD loop. |
| Stretch Damping | The damping for the stretch constraint using a value between 0 and 1. |
| Stretch Stiffness | The stiffness for the stretch constraint in GPa. |
| Stretch Stiffness Scale | This curve determines how much the stretch stiffness is scaled along each strand. The X-axis range is 0,1, where 0 maps to the root and 1 to the tip of the strand. |
| Collision Constraint | |
| Solve Collision | Enables solving of the collision constraint during the XPBD loop. |
| Project Collision | Enables the projection of the collision constraint after the XPBD loop. |
| Static Friction | The static function used for collision against physics assets. |
| Kinetic Friction | The kinetic friction used for collision against physics assets. |
| Strand Viscosity | The viscosity between 0 and 1 that is used for self-collision. |
| Grid Dimension | The dimension of the grid used to compute the viscosity force. |
| Collision Radius | The radius to be used for collision detection against physics assets. |
| Radius Scale | This curve determines how much the collision radius is scaled along each strand. The X-axis range is 0,1, where 0 maps to the root and 1 to the tip of the strand. |
| Strand Parameters | |
| Strands Size | The number of particles per guide that are used for simulation. |
| Strands Density | The density of strands measured in g/cm3. |
| Strands Smoothing | The smoothing between 0 and 1 for the incoming guide curves that leads to better stability. |
| Strands Thickness | The strands thickness in centimeters that are used for mass and inertia computation. |
| Thickness Scale | This curve determines how much the strands thickness is scaled along each strand. The X-axis range is 0,1, where 0 maps to the root and 1 to the tip of the strand. |
LOD Panel Properties
The following settings are found in the LOD panel:
| Property | Description |
|---|---|
| Simulation | Overrides the simulation used to represent this level of detail. Choose between the following:
|
Groom Component Properties
The following properties are available on a Groom component to override simulation settings set in the Groom Asset Editor.
Before a groom simulation can be overridden with a Groom component, the groom asset must first have Enable Simulation enabled in the Groom Asset Editor.
| Property | Description |
|---|---|
| Physics Asset | The physics asset to be used for hair simulation. |
| Simulation Settings | |
| Override Settings | Makes this component's settings override the groom asset physics settings. |
| Simulation Setup | |
| Reset Simulation | Make this simulation reset at some point in time. |
| Debug Simulation | Makes the simulation strands visible. |
| Local Simulation | Makes strands simulation be done in local space. |
| Linear Velocity Scale | The amount of linear velocities sent to the local groom space from the reference bone. |
| Angular Velocity Scale | The amount of angular velocities sent to the local groom space from the reference bone. |
| Local Bone | The name of the bone used for the simulation of local space. |
| Teleport Distance | Teleport distance threshold to reset the simulation. |
| Solver Settings | |
| Enable Simulation | Enables the simulation of the groom groups / levels of detail. Requires both this setting and the one in the groom asset to be enabled. |
| External Forces | |
| Gravity Vector | The acceleration vector measured in cm/s2 to be used for gravity. |
| Air Drag | The coefficient between 0 and 1 to be used for air drag. |
| Air Velocity | The velocity of the surrounding air measured in cm/s. |
| Material Constraints | |
| Bend Damping | Damping applied for the bend constraint using a value between 0 and 1. |
| Bend Stiffness | The stiffness for the bend constraint in GPa. |
| Stretch Damping | The damping for the stretch constraint using a value between 0 and 1. |
| Stretch Stiffness | The stiffness for the stretch constraint in GPa. |
| Static Friction | The static function used for collision against physics assets. |
| Kinetic Friction | The kinetic friction used for collision against physics assets. |
| Strand Viscosity | The viscosity between 0 and 1 that is used for self-collision. |
| Collision Radius | The radius to be used for collision detection against physics assets. |