Ue Udw Particles Lightning Wind Sounds

UDW particles, lightning, wind, sounds

All the rendered/heard weather effects: particles, lightning, wind systems, and sounds. For per-material weather (wetness/snow coverage on surfaces), see ue-udw-material-and-screen-effects.

When to use this skill

• Rain or snow not visible, or visible where it shouldn't be.
• Choosing between particle collision modes for perf vs flexibility.
• Lightning bolts striking specific actors as game logic.
• Adding wind force to physics objects or making chaos cloth react.
• Weather sounds going quiet at wrong times.
• Adding ambient outdoor audio (birds, insects, city) that changes with time/weather.
• Diagnosing VR splash particles only rendering in one eye.

Rain / Snow / Dust Particles

Three per-particle categories on UDW: Rain Particles, Snow Particles, Dust Particles. Each is controlled by the corresponding weather state value.

For shared behaviors (collision and spawning), see Shared Particle Settings below.

Splash Particles in VR

Weather Particle Collision

Set with Particle Collision Mode.

Simple Collision details

Line traces against simple collision geometry of the level. The particles trace on one channel — Weather Particle Collision Channel (default: Visibility).

Niagara particle traces are queries — meshes need queries enabled on their collision response.

GPU particles take a small number of valid particle paths and reuse them — still can be a significant CPU cost.

Particles not blocked when they should be (Simple Collision):

• Object lacks simple collision geometry. Traces only check simple collision.
• Collision profile isn't set to block the channel selected on UDW (default Visibility), with collision response Collision Enabled or Query Only (Niagara uses queries).
• Particles coming through a high ceiling: raise Ceiling Check Height on UDW.

Distance Field Collision details

Pure GPU emitters querying the global distance field.

Particles not colliding (Distance Field):

• Project not generating mesh distance fields.
• View Show → Visualize → Global Distance Field to see what particles actually see.
• For meshes that should block, enable Affect Distance Field Lighting.

Blocking particles without a mesh

UDS Occlusion Volume actor at Blueprints/Occlusion/ — enable its setting to block weather particles. Only available with Simple Collision mode.

Latency-free per-sphere blocking

For a moving space where particle collision latency is a problem (e.g. a player vehicle interior):

Only one Kill Sphere can be active at a time globally. Manage activation/deactivation manually for multiple.

Shared Particle Settings (Spawning)

In Shared Particle Settings. Particles spawn only in a volume around the camera; the illusion is they spawn everywhere.

Particles Not Visible

Lightning

Two types:

Both scale with the Thunder/Lightning value of current weather state.

Thunder sound settings live in the Sound Effects category — see below.

Manual lightning flash

Copy code
UDW.FlashLightning(customLocation, customTargetLocation)
// customLocation: optional; should be at cloud level (root of bolt)
// customTargetLocation: if nonzero, the bolt ends there

Lightning striking specific actors

Copy code
1. Add the UDW_Lightning Strikable Actor Interface to your actors
2. Implement "Test for Potential Lightning Strike":
   outputs: can-be-struck-now (bool) + world location where strike hits
3. On UDW → Lightning category:
   Enable "Enable Lightning Flashes Striking Actors"
4. Set "Fraction Of Lightning Flashes Which Can Strike Actors"
   (how many potential flashes go to actors when any are in range)
5. Implement the interface's "Struck by Lightning" event
   to spawn extra effects or run game logic

Lightning in Sequencer

Copy code
1. Add UDW to the sequence
2. Create Event → Trigger track on UDW
3. Add a keyframe; right-click for properties
4. Endpoint → Quick Bind → Flash Lightning
5. Configure custom location/seed in keyframe properties
6. Check Call in Editor to preview in the sequence editor

Wind

Wind Direction

Controlled separately from weather state via Wind Direction in Basic Controls + the Wind Direction category. Direction drives weather particles and cloud movement on UDS.

WOVs can override wind direction. If Apply Wind Direction is true on a WOV, the volume's wind direction wins as the player enters.

Wind Gusts

Wind intensity has a perlin-noise variation applied to simulate gusts. Settings in Wind Gusts: scale of variation, speed of the perlin noise.

Wind Debris

Small debris particles flying through the air when Wind Intensity is high. Category: Wind Debris.

Wind Directional Source

A Wind Directional Source is an engine component used by chaos cloth and SpeedTree assets. UDW makes and controls one with current wind by default.

Wind Physics Force

Apply wind force to physics-simulating objects. Add the Wind Physics Force component as a child of any primitive component simulating physics. At runtime, the component queries UDW wind state and line-traces to test exposure.

Wind Camera Shake

Enable in Wind Camera Shake to shake the player camera at max wind speeds.

Weather Sound Effects

Enabled by default for wind, rain, thunder. Category: Sound Effects.

Runtime control

Copy code
UDW.SetEnableWeatherSoundEffects(bool)   // toggle all
// Or set the per-sound Volume variables directly

All UDW sounds use the UDS_Weather sound class. Add it as a child of your project's Sound Effects class so weather sounds inherit your sound mix.

Sound Occlusion

Default: a simple system periodically traces from the camera and adjusts sound volume + low-pass filter (muffling) if the player is in an enclosed space. Toggle/adjust in Sound Occlusion category.

The actual occlusion calculation lives in Player Occlusion on UDS — see ue-uds-modifiers-configs-state.

Forced-occluded zones

Place a UDS Occlusion Volume actor (Blueprints/Occlusion/) to always-occlude a space. The Occlusion Sampling Mode in Player Occlusion decides if volumes are sampled.

Sound portals

UDS Occlusion Portal component. If instances exist around the occlusion sampling location, they're traced against and can negate occlusion when the trace is unobstructed. Use case: an open door/window letting outside weather sound naturally into the space.

Your own outdoor sounds following weather occlusion

Set your own sound sources to use the sound class UDS Outdoor Sound — they get occluded by the same volume attenuation as weather sounds.

Environment Sounds

System for general ambient outdoor audio (birds, insects, city ambience) that responds to time/weather and the sound occlusion. Sound Effects category on UDW selects the environment sound asset; a Forest ambience example ships.

Authoring an Environment Sound asset

Copy code
1. Make a new data asset of type UDS_Environment_Sound
2. Point at a metasound source asset (the actual sound played)
3. Tune volume + parameter overrides

Metasound source format

For sound occlusion and four-direction stereo panning, output format must be 5.1:

Directional audio is spatialized based on listener orientation and occluded directionally. Global audio is stereo, occluded by global occlusion.

Audio bus setup

Copy code
Source Settings:
   Enable Bus Sends: true
   Enable Base Submix: false
   + Post-Effect Bus Send → audio bus "UDS_Weather_AudioBus"

Reacting to Time/Weather/Wind

Five input parameters UDW sets on your metasound:

Included metasound nodes use these:

Reference: included Forest Example metasound source at Sound/MetaSounds/.

Runtime control

Copy code
UDW.ChangeEnvironmentSound(asset)  // change at runtime
UDW.ChangeEnvironmentSound(null)   // stop environment sounds

Gotchas

• Splash particles only in one eye in VR — Splash Particles Rendering Mode = Translucent.
• Particles not visible at all — invisible collision source blocking; or Show flags hiding sprites (Use Defaults); or Niagara compile fail (Full Rebuild on the asset).
• Particles ignore an interior space (Simple Collision) — ceiling too tall; raise Ceiling Check Height. Or use Weather Particles Kill Sphere for a moving interior.
• UDS Occlusion Volume doesn't block particles — Particle Collision Mode is Distance Field. Switch to Simple Collision (volume blocking is Simple-only).
• Lightning never strikes the player despite the interface — Enable Lightning Flashes Striking Actors is off, or Fraction Of Lightning Flashes Which Can Strike Actors is 0.
• Sounds go quiet at incorrect times — Sound Occlusion traces hitting surfaces they shouldn't. Adjust Player Occlusion on UDS (trace count, channel, update period).
• No sound from open door/window — add a UDS Occlusion Portal component to the door/window. Make sure traces can reach it.
• Wind doesn't affect chaos cloth / SpeedTree — Wind Directional Source category on UDW isn't enabled, or Disable when in interior is on and the actor is occluded.
• Wind Camera Shake doesn't trigger — Wind Intensity below the threshold band, or player is occluded.
• Environment Sound metasound playing but no panning/occlusion — output format isn't 5.1, or Post-Effect Bus Send to UDS_Weather_AudioBus is missing.
• Custom outdoor sound not occluded with weather — assign it the UDS Outdoor Sound class.

References & source material

Docs (Ultra Dynamic Weather 9.5):

• Rain Particles
• Snow Particles
• Dust Particles
• Weather Particle Collision (Simple / Distance Field / Kill Sphere / Occlusion Volume)
• Weather Particle Spawning
• Lightning (Flashes, Obscured, Flash Lightning, Strikable Interface)
• Weather Sound Effects
• Sound Occlusion (Portal, UDS Outdoor Sound)
• Environment Sound (metasound format)
• Wind Direction
• Wind Debris
• Wind Gusts
• Wind Directional Source
• Wind Physics Force
• Wind Camera Shake
• Common Issues — Weather (incl. VR splash, Simulate mode)

Plugin asset paths:

• Particles/ — Rain, Snow, Dust, Wind Debris niagara systems
• Particles/ — Lightning Strike + Obscured Lightning systems
• Sound/MetaSounds/ — included Forest Example environment sound metasound source
• Blueprints/Occlusion/ — UDS Occlusion Volume actor; UDS Occlusion Portal component
• Materials → UDS_Weather sound class; UDS_Weather_AudioBus audio bus
• Component classes: Weather Particles Kill Sphere; Wind Physics Force

Related skills: ue-udw-setup-and-state, ue-udw-spatial-weather (WOV wind override; UDS Occlusion Volume), ue-uds-modifiers-configs-state (Player Occlusion calculates occlusion; AmbientSound — Time and Weather Controlled is the simpler sound option), ue-udw-material-and-screen-effects (material wetness/snow accumulates from particle landing context).