Procedural Wind

Not Officially Released

This feature has not been officially released yet. It is planned for KawaiiPhysics v1.22. Specifications may change during development.

Overview

Hair and clothing drifting in a constant direction can look repetitive on an outdoor character. You may want to tune the timing of stronger and weaker wind as well as its direction.

Procedural Wind combines steady force with periodic changes, phase changes toward the tips, and random variation. Start with steady wind, then add the changes the scene needs. This makes it easier to see which setting changed the appearance.

AI-generated concept of clothing drifting with wind. It is not a measured motion trajectory.

Usage

1. Add an entry to the node's External Forces.
2. Set its type to Procedural Wind.
3. Raise Constant Force a little above 0.
4. Play the level.

Display Modes and Settings

Parameter Mode shows the main settings in Simple and every setting in Advanced. Values hidden in Simple mode still contribute to the calculation.

Wind Settings

Change you want	First settings to tune
Direction or steady strength	Wind Direction, Constant Force
Periodically stronger and weaker wind	Sway Force and Sway Period in Advanced mode
A delay from roots toward tips	Ripple Force, Ripple Tip Phase Delay
Less regular variation	Random Force, direction noise

Wind Components and Composition

Component	Purpose
Constant	Wind with a constant strength
Sway	A wave that moves all bones in the same phase
Ripple	A wave that travels from root to tip
Strength Cycle	Periodic multiplier applied to Constant, Sway, and Ripple
Random	Smooth noise that varies wind strength
Gust	A gust triggered through the API

The components are combined as follows.

Total = (Constant + Sway + Ripple) * StrengthCycle + Random + Gust

Ripple Tip Phase Delay controls the phase delay at the tip. At 0 there is no wave propagation; negative values reverse propagation from tip to root. Wind Direction Noise Angle and Wind Direction Noise Period also vary the direction itself.

Procedural Wind Gust / Transient External Force

When an event needs stronger wind, editing ordinary wind values also means managing when to restore them. A Gust adds a short wind with specified rise, hold, and decay. For animation timing, put its trigger on a Notify track.

1. Open the Animation Sequence.
2. Move to the point where the gust should start.
3. Add KawaiiPhysics: Trigger Gust to its Notify track.
4. Raise Strength a little above 0 and set a positive total time, for example RiseTime=0.2 s and DecayTime=0.5 s. All three times default to 0.
5. Play the animation.

Concept: a gust rises, holds, then fades.

Check for stronger wind at that point followed by a fade. The Notify's total time is RiseTime + HoldTime + DecayTime. For gameplay events that need early cancellation, a programmer can manage stopping with a handle-based API.

Progress depends on animation evaluation. Check conditions where LOD or URO stops evaluation. The transient-force reference covers lifetimes, the 8-entry limit, and unsupported reference types.

Wind Preset Data Asset

Re-entering wind values for another outfit or scene takes time and makes comparison harder. Saving wind presets lets you choose previously tuned values. Keep this separate from the whole-node UKawaiiPhysicsPresetDataAsset.

1. Select the target Kawaii Physics node.
2. Open Wind Scope in Details.
3. Choose the target Procedural Wind under Force.
4. Open Presets.
5. Select Breeze.

Wind direction remains on the target. See wind preset APIs for the eleven saved fields and runtime application conditions.

To save custom wind, assign a Wind Preset Data Asset (WindScopePresetDataAsset) under Project Settings > Plugins > Kawaii Physics > Wind Scope, then use Save as Preset > Add New Preset in Wind Scope. Saving is unavailable with only built-in presets.

Wind Scope application modifies the ABP and also sets Enabled=true and TimeScale=1, whereas runtime application preserves these two fields. See Wind Scope for saving and overwriting.

Local, Shared, and Auto

The Shared and Auto wind sources use a Kawaii Physics Shared Publisher in the same Actor family. Match Shared Wind Tag to the publisher's Shared Group Tag.

• Shared uses wind parameters from the publisher. While the publisher is absent, it keeps advancing locally.
• Auto uses Shared while a publisher exists and Local otherwise.
• Phase offsets, Seed, Time Scale, enabled state, bone filters, and space remain configured on each node during sharing.

Seed is shared by Random and direction noise. Matching values can reproduce those fluctuations, but edits during PIE take effect on the next play session. It does not guarantee identical simulation results across all environments.

For programmatic updates to shared parameters or gusts, see Shared Publisher runtime control.

Related UE documentation

• Animation Notifies — Review Notify tracks, NotifyState intervals, and event firing conditions. (UE 5.8)
• Data Assets — Review data stored in assets and instances of existing Data Asset classes. (UE 5.8)