This release merges VBSNG's flagship volumetric cloud system NubisClouds into the main branch. Re-implemented from Schneider/Vos 2015 SIGGRAPH (Horizon Zero Dawn), supplemented with Schneider 2017 GPU Pro 7, Hillaire 2016 Frostbite, and Häggström 2018 thesis. In-cloud flight, dawn/dusk transitions, and through-cloud light all feel physically right.
1 · Noise & Geometry
- Multi-frequency procedural noise: Perlin-Worley base shape (64³ RGBA16F) + Worley FBM detail erosion (32³) + 2D curl noise (128²); all compute-generated once
- Spherical-shell cloud geometry: base 1500 m / top 5000 m (configurable); matches Earth curvature, distant clouds sink at horizon
- Four cloud-type blend: stratus / stratocumulus / cumulus / cumulonimbus, UI-smooth transitions by altitude gradient
2 · Lighting Model
- Beer-Powder lighting: HZD's signature Beer-Powder combined with Beer-Lambert — correct "powdered sugar" edge
- Multiple scattering approximation: 3-order Wrenninge sum (
Σ 0.5ⁿ · exp(-k·0.5ⁿ · d)); diffuse warmth inside the cloud - Dual HG phase: forward HG (g=0.7) for sun-side silver lining; backward HG (g=-0.25) for backlight rim
3 · Performance Optimization
- Adaptive sampling: low-density regions use cheap mode (base shape only); on hit, step back and switch to expensive (full detail + 6-tap sun cone)
- Depth-aware occlusion: scene-depth driven geometric occlusion — mountains, buildings, aircraft block clouds correctly
- Wind drift: CPU-accumulated wind vector, no discontinuous morph evolution
4 · UI Real-time Controls
Cloud base height / top / coverage / density / type / detail strength / lighting parameters / sample count — all wired to ImGui for live adjustment. Instructors can freeze a weather preset in the scenario editor for reuse.
Key Parameters
- Sample steps: 96–160 raymarch + 6-tap sun cone
- Cloud top: default 5 km, up to 18 km
- Noise textures: noise_low 64³ + noise_high 32³ + curl 128², compute-generated once
- Phase function: Dual HG (front 0.7 / back -0.25)
- Multiple scattering: 3-order Wrenninge approximation
References
- Schneider, Vos. The Real-time Volumetric Cloudscapes of Horizon Zero Dawn. SIGGRAPH 2015
- Schneider. Nubis: Authoring Realtime Volumetric Cloudscapes with the Decima Engine. GPU Pro 7, 2017
- Hillaire. Physically Based Sky, Atmosphere and Cloud Rendering in Frostbite. 2016
- Häggström. Real-time rendering of volumetric clouds. MSc Thesis, 2018