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Volumetric Lighting Cookbook

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Bradley Brown edited this page Aug 13, 2026 · 1 revision

Volumetric Lighting Cookbook

Copy-paste recipes for the Fracturing Fog volumetric system. Each recipe lists exact control values, explains why it works, and offers variations. For what each control means, see the Volumetric Lighting Guide.

Companion pages: User Index · Volumetric Lighting Guide · User Bulb 3D Guide

All controls are in Lighting & FX (Fractal Params → Open Lighting & FX…), across the Lights, Shadow, and Fog / Volumetric expanders. Colors are AARRGGBB hex; keep alpha FF.

Contents

The three rules of god rays

God rays (crepuscular rays, light shafts) are just fog that is bright where light reaches it and dark where the fractal blocks the light. Three things must all be true or you get flat haze instead of shafts:

  1. Fog to light up — Fog density > 0 and Volume steps > 0.
  2. Something to cast the shadow — Shadow steps > 0. Without shadows nothing carves the dark gaps between shafts. This is the #1 reason shafts don't appear.
  3. A reason to glow toward the light — Anisotropy > 0, and the light positioned behind/beside the fractal relative to the camera, so the fractal occludes it and the shafts fan out toward you.

Everything else (clouds, color, palette) is styling on top of those three.

Note

These recipes are tuned for the 3-D fractals (Mandelbulb, Mandelbox, Quaternion, KIFS, …), whose geometry fills the frame at unit scale. On Relief 3D (2-D heightfield terrain) the same knobs work but the numbers differ — the fog is bounded to the terrain's height band and the air path is shorter, so you need higher Fog density, and shafts show against the sky only in the band just above the ridge. The default GPU relief path also uses the key light only for fog, and Palette map doesn't apply to relief yet. See the relief-specific caveats in the Relief 3D Cookbook → Foggy valley with god-rays.

Tuning workflow

Dial in this order — each step builds on the last:

  1. Density first. Set Volume steps to 16 and raise Fog density until the depth reads right (~0.1–0.2 for most scenes). Ignore shafts for now.
  2. Add shafts. Turn Shadow steps to 24. Reposition Light 1 (θ/φ) so it sits behind the fractal from the camera's view — shafts appear in the gaps.
  3. Shape them. Raise Anisotropy to 0.5–0.8 for forward punch; adjust Softness k for edge hardness.
  4. Color (optional). Raise Light 2/3 intensity for colored fill, or set a Fog color, or turn up Palette map.
  5. Clouds (optional). Raise Volume noise, set Noise scale, add Self-shadow for internal structure.
  6. Quality pass. Raise Volume steps to 32–48 for the final render.

1 · Classic god rays (crepuscular shafts)

Bright white shafts fanning through gaps in the fractal — the signature look.

Control Value Control Value
Fog density 0.15 Volume steps 28
Height falloff 0 Anisotropy 0.7
Shadow steps 24 Softness k 8
Light 1 intensity 1.2 Fog color FFFFFFFF

Why: density gives the fog something to light; shadow steps let the fractal carve dark lanes; positive anisotropy concentrates the glow toward the light so the lit lanes read as beams. Position Light 1 behind the fractal (try θ ≈ 3.9, φ ≈ 1.2) and orbit the camera until the silhouette breaks the light into shafts.

Variations:

  • Softer, dustier shafts: Anisotropy 0.4, Softness k 3.
  • Laser-sharp shafts: Anisotropy 0.85, Softness k 24.
  • Add floating dust: Volume noise 0.2, Noise scale 1.5.

2 · Soft depth haze (atmospheric perspective)

No shafts — just distance fading to atmosphere, so far parts of the fractal recede. Cheap and subtle.

Control Value
Fog density 0.08
Volume steps 0 (flat exp-fog is enough)
Shadow steps 0
Anisotropy 0

Why: with Volume steps = 0 you get pure Beer–Lambert extinction — distant geometry blends toward the sky gradient with almost no cost. Set the Sky top / bottom colors (Sky / Environment expander) to control the haze tint.

Variations:

  • Warmer haze: sky bottom color to a warm grey (FFB9A88C).
  • Add faint glow: Volume steps 12, Anisotropy 0.3 — barely-there shafts.

3 · Ground mist / valley fog

Fog pools low and clears overhead — mist clinging to the base of the fractal.

Control Value Control Value
Fog density 0.4 Height falloff 2.0
Volume steps 24 Anisotropy 0.5
Shadow steps 24 Volume noise 0.3
Noise scale 0.6 Noise speed 0.05

Why: Height falloff scales density by exp(-2·y), so fog is dense near y = 0 and thin above. The gentle noise + slow drift keeps the mist alive. Aim the light low (φ near 1.4–1.6, near the horizon) to rake shafts across the mist.

Variations:

  • Thicker soup at the base: Fog density 0.7, Height falloff 3.0.
  • Higher fog line: lower Height falloff to 1.0.

4 · Static volumetric clouds

The fog breaks into cloud masses surrounding the fractal.

Control Value Control Value
Fog density 0.5 Volume noise 0.85
Volume steps 32 Noise scale 0.5
Shadow steps 24 Noise octaves 5
Anisotropy 0.6 Noise speed 0

Why: high Volume noise swings density between empty space and dense clumps; low Noise scale makes big soft masses; 5 octaves adds wispy edges. Shadow steps

  • anisotropy still give shafts between the clouds.

Variations:

  • Wispier: Noise scale 1.5, Noise octaves 6.
  • Denser cumulus: Fog density 0.8, Volume noise 1.0.
  • Add internal shadow depth: see Recipe 10.

5 · Drifting clouds (animated)

Recipe 4, but the clouds move — ideal for video / slideshow.

Control Value
(start from Recipe 4)
Noise speed 0.3
Light orbit speed 0.1 (optional — sweeps the shafts too)

Why: Noise speed advects the FBM lookup over scene time so the clouds roll. Use the Start/Stop button next to the field to freeze on a good frame without losing the rate. Pair with a slow Light orbit for shafts that sweep as the clouds drift.

Tip: keep Noise speed small (0.05–0.4). Fast drift looks like boiling, not weather.

6 · Cathedral shafts (warm, colored)

Warm, sacred window-light shafts — think sun through stained glass.

Control Value Control Value
Fog density 0.18 Volume steps 32
Shadow steps 28 Anisotropy 0.75
Softness k 12 Fog color FFFFE0B0 (warm)
Volume noise 0.15 Noise scale 1.2

Why: hard-ish shadows (high softness k) + strong forward anisotropy make crisp, defined beams; the warm Fog color tints the whole medium golden even under a white key light. A little noise adds drifting dust motes in the beams.

Variations:

  • Cooler, moonlit chapel: Fog color FFB8CCFF, lower Light 1 intensity to 0.7.
  • Dustier air: Volume noise 0.3, Noise scale 2.0.

7 · Colored medium — amber haze & teal mist

Fog with its own color, independent of the (white) lights. Two presets:

Amber haze

Control Value
Fog density 0.2
Volume steps 24
Shadow steps 24
Anisotropy 0.5
Fog color FFFFCC00

Teal mist

Control Value
Fog density 0.25
Volume steps 24
Shadow steps 24
Anisotropy 0.4
Fog color FF66CCFF

Why: Fog color multiplies the accumulated in-scatter, so the whole medium takes that hue while the lights stay neutral. This is the cleanest way to set a single fog mood. Compare with Recipe 8, where the lights (not the medium) provide color.

8 · Three-light stage lighting

Colored fog from multiple directions — white key, cool blue fill, warm amber rim. Uses the pre-colored Lights 2 and 3, so no color editing needed.

Control Value Control Value
Light 1 intensity 1.0 (white key) Light 2 intensity 0.8 (blue fill)
Light 3 intensity 0.6 (amber rim) Fog density 0.2
Volume steps 32 Shadow steps 24
Anisotropy 0.6 Fog color FFFFFFFF

Why: each light with intensity > 0 injects its own color into the fog. Light 2 defaults to cool blue (B0C8FF), Light 3 to warm amber (FFC890), so the fog picks up blue on one side and amber on the other — cinematic color contrast with a neutral medium.

Only Light 1 casts shadow shafts by default; Lights 2/3 add colored glow without carved shafts. That's usually the desired look (one hero shaft, colored ambience). To give all three shafts, set ShadowLightMask = 0x7 in a saved scene/preset.

Variations:

  • Push the contrast: Light 2 intensity 1.2, Light 3 1.0.
  • Custom light colors: set them in the Control Center's Color & Light section or a saved scene.

9 · Back-scatter rim halo

The glow appears when the light is behind the camera — a soft halo rimming the fractal instead of shafts toward the light. Ethereal, backlit-cloud feel.

Control Value
Fog density 0.3
Volume steps 28
Shadow steps 16
Anisotropy −0.5
Volume noise 0.4

Why: negative anisotropy peaks the phase function away from the light, so fog glows brightest where the light comes from behind you. Combine with clouds for a "sun behind the storm" edge glow.

Variations:

  • Stronger halo: Anisotropy −0.75.
  • Mix forward + back by animating anisotropy across a scene keyframe track.

10 · Stormcloud with internal god-ray banding

Dense clouds that self-shadow, producing dark-to-light banding inside the cloud body — the depth that flat clouds lack.

Control Value Control Value
Fog density 0.7 Volume noise 1.0
Volume steps 40 Noise scale 0.5
Shadow steps 24 Noise octaves 5
Anisotropy 0.6 Self-shadow 2.5
Noise speed 0.15 Self-shadow steps 8

Why: Self-shadow marches each cloud sample toward the light through the FBM density, darkening the far side of each clump — you see light bleed through the near edge and fall off into the body. Costs extra, so add it last and keep Self-shadow steps modest.

Variations:

  • Backlit thunderhead: combine with Anisotropy −0.4 (Recipe 9).
  • Lighter cumulus: Fog density 0.5, Self-shadow 1.5.

11 · Underwater shafts + caustics

Light shafts stabbing down through water, with rippling caustic highlights on upward faces. Combines volumetrics with the caustics FX.

Control Value Expander
Fog density 0.3 Fog / Volumetric
Volume steps 32 Fog / Volumetric
Height falloff 0.5 Fog / Volumetric
Anisotropy 0.7 Fog / Volumetric
Fog color FF2E6E7E (deep teal) Fog / Volumetric
Shadow steps 24 Shadow
Caustics strength 0.8 (Reflection/Edge/… — caustics)
Caustics speed 0.4 Lights

Why: teal fog color + downward key light + forward anisotropy = classic underwater shafts; the animated caustics add the dancing surface-refraction highlights. Aim Light 1 near-vertical (φ small).

Variations:

  • Murkier depths: Fog density 0.6, Fog color FF1E4A55.
  • Add drifting particulate: Volume noise 0.3, Noise speed 0.1.

12 · Nebula / cosmic volumetrics

The fog takes the fractal's own color theme — glowing gas clouds in the palette of the surface. This is the palette map (layer D) at work.

Control Value Control Value
Fog density 0.5 Volume noise 0.9
Volume steps 36 Noise scale 0.4
Shadow steps 16 Noise octaves 6
Anisotropy 0.4 Palette map 0.7
Noise speed 0.1 Fog color FFFFFFFF

Why: Palette map recolors the lit fog by the active 3D color theme's gradient, keyed by fog depth — thick regions pull one end of the ramp, thin regions the other. With cloudy noise this reads as a nebula whose colors match the fractal. Pick an expressive color theme first; the fog inherits it.

Variations:

  • Fog fully in the theme palette: Palette map 1.0.
  • Blend palette with a base tint: Palette map 0.4 + a Fog color.

13 · Psychedelic dream fog

Maximum palette map — surreal, non-realistic color that binds fog and fractal into one shifting palette.

Control Value
Fog density 0.4
Volume steps 32
Shadow steps 12
Anisotropy 0.3
Volume noise 0.6
Noise speed 0.25
Palette map 1.0

Why: at full strength the fog is entirely theme-colored; animated noise makes the palette swirl. Deliberately not physical — pair with a vivid, high-contrast color theme for the strongest effect.

14 · Horror: single hard shaft

One stark, hard-edged beam in near-blackness — dread, interrogation-lamp energy.

Control Value Control Value
Fog density 0.25 Volume steps 32
Shadow steps 32 Softness k 40 (very hard)
Anisotropy 0.85 Ambient 0.03 (Lights)
Light 1 intensity 1.5 Fog color FFDDE6FF (cold)

Why: high softness k + high anisotropy make one tight, sharp shaft; crushing the Ambient to near-zero drops everything else into darkness so the single beam dominates. Position Light 1 to rake across the fractal at a steep angle.

15 · Sweeping searchlight (animated)

A shaft that sweeps across the scene over time — great for video loops.

Control Value
Fog density 0.2
Volume steps 28
Shadow steps 24
Anisotropy 0.75
Light orbit speed 0.4

Why: Light orbit speed rotates Light 1 around world-Y (Lights 2/3 follow at 0.7× and 1.3×, desynced), so the shafts swing through the frame. Use Start/Stop to hold a frame. Keep the rate low for a stately sweep.

Variations:

  • Multi-color sweep: raise Light 2/3 intensity (Recipe 8) so blue and amber shafts chase each other at different speeds.

Advanced combinations

  • Volumetric + Relief 3D — volumetrics work with the Relief 3D raymarch; fog wraps the raised relief for dramatic depth.
  • Color layers stack — light color (Recipe 8) × fog color (Recipe 7) × palette (Recipe 12) all compose. E.g. blue fill light + amber fog color + low palette map = a complex, film-graded atmosphere.
  • Scene Engine keyframes — animate Anisotropy from −0.5 → +0.8 across a shot to swing from back-halo to forward shafts as the camera moves; or ramp Palette map 0 → 1 to dissolve realistic fog into a dream palette.
  • Slideshow — volumetric settings are part of the saved scene, so they carry through slideshow cross-fades.

Troubleshooting

Symptom Cause Fix
Fog is flat, no shafts Shadow steps = 0 Raise Shadow steps to 24+.
Still no shafts Light not occluded by the fractal Move Light 1 (θ/φ) behind the fractal from the camera view.
Shafts too weak / even Anisotropy near 0 Raise to 0.5–0.8.
Whole image washed white Fog density too high Lower toward 0.1–0.3; check Light 1 intensity.
Clouds look like static/noise Noise scale too high Lower to 0.4–0.8 for soft masses.
Clouds "boil" in video Noise speed too high Lower to 0.05–0.3.
Colored fog looks muddy Light color and fog color both strong Pick one color source (lights or fog color), leave the other neutral.
Fog color ignored Value is white FFFFFFFF Set a non-white Fog color, or it's a ×1 no-op.
Palette map does nothing Strength 0, or theme has a flat gradient Raise Palette map; pick an expressive color theme.
No fog at all on UserBulb GPU UserBulb GPU path skips volumetrics Render UserBulb on the CPU (turn off Use GPU render).
Render is slow High Volume steps × Shadow steps + self-shadow Tune at 12–16 steps; rely on adaptive LOD; use GPU where supported.

See also

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