Tutorial Skirt en

Skirt Physics Setup

日本語版

This tutorial explains how to set up skirt physics.

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Prerequisites

• Completed Quick Start
• SkeletalMesh with skirt bones

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Skirt Challenges

Compared to hair, skirts have these challenges:

1. Multiple bone chains - Multiple chains around the skirt
2. Leg penetration - Legs easily penetrate the skirt during walking
3. Bone distance - Adjacent chains may separate too much

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Basic Skirt Setup

Single Chain Setup

First, set up one bone chain.

Reference Parameters

Parameter	Reference	Description
Damping	0.2-0.3	Moderate damping
Stiffness	0.1-0.2	Shape retention
World Damping Location	0.7-0.9	Stability during movement
World Damping Rotation	0.7-0.9	Stability during rotation
Limit Angle	45-90	Allow larger sway
Gravity	(0, 0, -0.3)	Light gravity

Multiple Chain Setup

If the skirt has multiple bone chains:

1. Method 1: Multiple KawaiiPhysics nodes

   • Use separate nodes for each chain
   • Can adjust settings individually

2. Method 2: Single node for multiple chains

   • Set common parent bone as Root Bone
   • All chains operate with same settings

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Bone Constraint (Maintaining Bone Distance)

To prevent adjacent bone chains from separating too much, use Bone Constraint.

Note: Promoted to Production Ready in v1.19.

Setup Method

1. Open Bone Constraints section
2. Add bone pairs
   • Bone1: Left side bone (e.g., skirt_L_01)
   • Bone2: Right side bone (e.g., skirt_R_01)
3. Similarly, add adjacent bone pairs

Reference Settings

Parameter	Reference
Global Compliance Type	Soft
Constraint Iteration Count (Before)	1-2
Constraint Iteration Count (After)	1-2

Notes

• May increase processing load
• Use DataAsset to share settings across multiple AnimBPs
• Supports regex-based bone configuration

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Sync Bone (Leg Penetration Solution)

Added in v1.20

Sync Bone is a feature that synchronizes skirt bones with the movement of reference bones (such as legs). This allows you to implement penetration countermeasures that previously required ControlRig or PoseDriver, all within the KawaiiPhysics node.

How It Works

Applies the displacement from reference pose of the source bone (Source Bone) to the target bones (Target Bones).

Setup Method

1. Open Sync Bones section
2. Source Bone: Set the reference bone (e.g., thigh_L)
3. Target Bones: Set the skirt bones to be affected
4. Distance / Ratio / Amount: Configure movement adjustment parameters

Use Cases

• Skirt rises when leg is lifted
• Skirt follows leg movement during walking

Benefits

• No additional ControlRig or PoseDriver setup required
• Self-contained within KawaiiPhysics node
• Naturally integrates with physics simulation

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Preventing Leg Penetration (Collision)

Prevent legs from penetrating the skirt during walking.

Tip: Combining with the Sync Bone feature added in v1.20 provides more natural results.

Using Capsule Limits

Capsule Limits are suitable for legs.

Setup Steps

1. Add Capsule Limits
2. Set Driving Bone to thigh bone (e.g., thigh_L)
3. Adjust capsule position with Offset
4. Adjust capsule thickness with Radius
5. Adjust capsule length with Length
6. Set up similarly for the other leg

Multiple Collisions

To cover entire legs:

• Thigh capsules (left and right)
• Knee to calf capsules (left and right)

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Pleated Skirt vs Flare Skirt

Pleated Skirt

Skirts with folds need to maintain their shape.

• Higher Stiffness (0.2-0.3)
• Smaller Limit Angle (30-45)

Flare Skirt

Flowing skirts express soft movement.

• Lower Stiffness (0.05-0.1)
• Lower Damping (0.1-0.2)
• Larger Limit Angle (60-90)

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Using Curve Data

Express different movement at waist vs hem.

Example: Softer Hem

Stiffness Curve Data:

• X=0.0 (waist): Y=1.0
• X=1.0 (hem): Y=0.3

Example: Smaller Collision at Hem

Radius Curve Data:

• X=0.0 (waist): Y=1.0
• X=1.0 (hem): Y=0.5

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Troubleshooting

Skirt is erratic

• Increase World Damping
• Decrease Limit Angle
• Check Teleport Distance Threshold

Legs penetrate skirt

• Add Capsule Limits
• Increase collision Radius
• Cover entire legs with multiple collisions

Bone chains separate

• Set up Bone Constraint
• Add adjacent bone pairs

Poor performance

• Lower Constraint Iteration Count
• Reduce number of collisions
• Disable Update Physics Settings In Game

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Related Links

• Parameter Reference - All parameter details
• FAQ - Frequently asked questions
• Hair Setup
• Accessories Setup