Unreal Engine plugin · Documentation

Unreal Engine 5.4 to 5.8
C++ runtime
Windows

Caligo.
Smoke and fog.

Caligo draws smoke and fog as real volumes: ground fog that wraps around your set, fog banks that roll in, columns of smoke bending in the wind, coloured smoke bombs, balls of smoke that grow and fade, and full-frame smoke with fine curling wisps. Each effect is ray marched through animated 3D noise inside a box, lit by your sun or its own key light, with soft self-shadows.

Every frame is a function of the time only, with no simulation that builds up frame after frame. Scrubbing in Sequencer and rendering with Movie Render Queue show the exact same frames, and the smoke is already there on the first frame.

A stone colonnade in thick ground fog, lit by a low sun behind the columns

Quick start
Blueprints
Presets
Puffs and Sequencer
Settings
Performance
Compatibility
Support

Quick start

Enable Caligo Smoke & Fog in Edit > Plugins and restart the editor.
Open the sample level /Caligo/Maps/Caligo_Showcase. In the Content Browser, use Settings > Show Plugin Content, then Plugins > Caligo Content > Maps. It has 18 numbered booths, one per preset, with the settings written on the wall.
Turn on Realtime in the viewport (Ctrl+R) to see the smoke move in the editor.
In your own level, drop BP_Caligo (Plugins > Caligo Content > Blueprints) and pick an effect in its Preset dropdown.
Set the size of the box with Size. The smoke lives inside it and thins out before its sides, so the box never shows.

The Caligo sample level: rows of numbered booths filled with fog and smoke — The sample level.

Contact sheet of the 18 sample booths — The 18 booths, one per preset.

Blueprints

BP_Caligo (Plugins > Caligo Content > Blueprints) is the easiest way in:

Drop it in your level.
Pick an effect in its Preset dropdown. The list has all 18 presets: fog (Fog), rising smoke (Smoke), puffs (Puffs) and smoke that fills a volume (Fill). The settings change at once.
Tweak Volume, Motion, Look and Lighting as you like.

The C++ classes Caligo Fog, Caligo Smoke, Caligo Puffs and Caligo Fill do the same, each with its own presets. All of them can be extended in Blueprints.

Spawn Caligo is a Blueprint node for gameplay. It puts any preset at a transform. A Puffs preset fires one burst at once and the actor removes itself when the smoke has faded. Other presets stay until you destroy them, unless you set Life Span. For example: On Hit > Spawn Caligo (Puffs: Impact) at the hit point.

Presets

Fog

Preset	Look
Ground Fog	Low fog hugging the ground and rolling slowly around objects.
Fog Bank	A thick wall of fog moving in.
Mist	Patches of thin mist drifting through the volume.
Rolling Fog	Fog that tumbles over itself, as from a fog machine.

Smoke

Preset	Look
Plume	A column of grey smoke rising and bending in the wind.
Black Smoke	Thick dark smoke, as from burning oil.
Smoke Bomb	Dense coloured smoke pouring out of a canister.
Steam	White steam, fast and quickly gone.
Fire Smoke	Smoke lit from below by the fire it comes from.

Puffs

Preset	Look
Puff	One ball of smoke that grows, rolls and fades.
Impact	A quick puff thrown off a hit.
Explosion	A cloud of eight puffs bursting out.
Smoke Balls	Round puffs popping up one after another.
Drifting Puffs	Long puffs drifting sideways.

Fill

Preset	Look
Full Frame	Smoke filling the frame with veils and fine curling wisps.
Pour In	Smoke pouring in from one side, from `Start Time`.
Dark Billows	Dark, heavy billows.
Haze	A light veil of smoke with fine wisps.

Fog and Plume presets sit on the actor, which is the ground. Puffs and Fill presets are centred on it. Pour In pours along the actor's X axis, so rotate the actor to choose the side the smoke comes from.

Full-frame grey smoke on black, with veils and thin curling wisps — Fill: Full Frame, pouring in from the left.

Several round balls of smoke on black — Puffs: Smoke Balls.

Puffs and Sequencer

Puffs presets fire bursts of puffs. The Bursts settings say when:

Trigger	When a burst goes off
Repeat	Every `Interval` seconds from `First Burst`.
Beats	On music beats: `BPM` and the list of `Beats` (1 = the first beat, at time 0).
Times	At the exact times of the `Times` list, in seconds.
On Fire	Only when Fire is called from Blueprint.

Fire works in every mode, on top of the scheduled bursts. Up to 8 puffs are drawn at a time (the youngest).

With Follow Sequencer ticked (the default), every Caligo actor reads the time of your sequence:

in the editor, it follows the Sequencer playhead, so scrubbing shows each frame exactly;
in game and in Movie Render Queue, it follows the Level Sequence that is playing;
without an open or playing sequence, it runs on the world clock.

To put a puff on a frame:

Scrub to the frame.
Select the actor and click Add Burst At Playhead. The trigger switches to Times.
Click again on other frames to add more. Clear Bursts starts over.

For full manual control, tick Use Custom Time and key Custom Time yourself. Time Scale gives slow motion, and Time Offset starts the smoke further along.

Movie Render Queue. Each pixel marches its ray with a small random offset that changes every sample. Render with 8 or more spatial samples for smooth smoke.

Settings

Volume

Shape: Layer (fog on the ground, up to Layer Height), Plume (a column from the bottom centre), Puffs (balls fired by bursts) or Fill (the whole volume, as full as Coverage says).
Size: the box the smoke lives in.
Edge Fade: the smoke thins out over this distance near the sides of the box. The distance wanders with the noise, so the sides never show as straight lines.
Coverage: how much of the volume is filled.
Layer: Layer Height, Layer Softness and Layer Roll (how high the top of the fog rolls up and down).
Plume: Plume Radius, Plume Spread (how fast it widens) and Plume Fade (where it has thinned out).
Fill: Pour, Pour Speed and Pour Softness. The smoke pours in along X from Start Time.
Puffs: Puff Radius, Puff Count, Puff Spread, Puff Stagger, Puff Size Random, Puff Growth (time to reach its size), Puff Life, and Puff Velocity, Puff Velocity Random and Puff Drag (the launch, slowed by the air).

Motion

Wind: the air carrying the smoke, in cm/s.
Rise: hot smoke drifting up, in cm/s. A plume rises at this speed and bends with the wind.
Turbulence, Turbulence Scale and Evolution: the swirls. They set how far the swirls push the smoke, how big they are, and how fast they change. Strong swirls bend the outlines and stretch the smoke into curls.

Look

Density: how much light 1 m of smoke stops.
Noise Scale: the size of the billows.
Billows: round cauliflower billows (1), or smooth veils of smoke (0).
Detail: fine detail that frays the edges. Wisps and Wisp Scale: thin curling filaments around the smoke.
Color: white for steam and fog, grey for smoke, dark for soot, a colour for a smoke bomb.
Brightness and Exposure Independent: brightness stays the same at any exposure, so a preset looks the same in any level. Untick it to light the smoke in scene units.
Ambient and Ambient Color: soft light from all around. Backlight: how much the smoke glows when lit from behind. Self Shadow: how dark the smoke's own shadow is.
Glow Color, Glow Intensity, Glow Radius and Glow Offset: light from inside the smoke, such as a fire under its smoke.
Steps: samples along each ray (96 by default). More is smoother and slower.

Lighting and time

Source: Scene uses the brightest Directional Light of the level (the sun). Custom uses Light Direction and Light Color. Light Intensity: the strength of the key light.
Seed changes the pattern. Follow Sequencer, Use Custom Time, Custom Time, Time Scale, Time Offset, and Start Time (when pouring smoke starts).

Ground fog rolling around dark blocks — Fog: Ground Fog wraps around the set.

A grey plume and a fire-lit plume rising on black — Smoke: Plume and Fire Smoke.

Performance

The smoke is drawn by its material, one draw per actor. The cost grows with the area it covers on screen and with Steps.
Empty parts of the box are skipped quickly. Lower Steps for smoke far from the camera.
Measured on an RTX 3090 at 1080p: smoke covering about 80% of the screen with the default 96 steps adds about 6 to 15 ms per frame. Lower Steps for a cheaper effect.

Compatibility

Unreal Engine 5.4, 5.5, 5.6, 5.7 and 5.8, Windows. Runtime module: works in packaged games.
The smoke is lit by one key light (the sun or its own), an ambient light and its own glow. Point lights and spot lights of the level do not light it.
The smoke does not cast shadows on the set, and does not receive them.
The smoke is drawn in the translucency pass without depth test, so the camera can fly into it. Rays stop on opaque geometry.
Not network replicated: the smoke is cosmetic. Call Fire from your own replicated gameplay code.

Support

Questions and bug reports: contentcreatorassetspack@gmail.com. Tell us your engine version and, if you can, attach a screenshot of the actor's settings.

Caligo.Smoke and fog.