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HERO// P / vbsng-meteor

The hard part of training weather isn't the look of distant clouds — it's the truth of in-cloud flight: continuous visibility transitions, physically reasonable wind gust scales, and low-level wind shear that actually challenges the crew.

1 · Volumetric Clouds — NubisClouds (HZD style)

Re-implemented from Schneider/Vos 2015 SIGGRAPH · HZD's signature Beer-Powder lighting

Simulation Effects

  • Multi-frequency procedural noise: Perlin-Worley base shape (64³ RGBA16F) + Worley FBM detail erosion (32³) + 2D curl noise (128²) for atmospheric turbulence, all generated once by compute shader
  • Spherical-shell cloud geometry: two-layer shell (base 1500 m / top 5000 m, configurable), naturally matches Earth curvature, distant clouds sink to the horizon
  • Four cloud-type blend: stratus / stratocumulus / cumulus / cumulonimbus, UI-smooth transitions
  • 3-order Wrenninge multiple-scattering approximation: cloud interior shows true "self-glowing" diffuse warmth
  • HZD's signature Beer-Powder formula combined with traditional Beer-Lambert attenuation — correctly reproduces the "powdered-sugar" edge
  • Dual HG phase: forward HG (g=0.7) gives sun-side silver lining; backward HG (g=-0.25) gives backlight rim

Key Parameters

  • Cloud Model: Volumetric ray-march 96–160 steps + 6-tap sun cone
  • Noise Textures: noise_low 64³ + noise_high 32³ + curl 128², compute-generated once
  • Cloud Top: up to 18 km
  • Wind Drift: CPU-accumulated wind vector, no discontinuous cloud morph evolution

2 · Atmospheric Scattering

Bruneton/Néyret 2008 precomputed atmosphere · coupled with time-of-day

Simulation Effects

  • Sky, sun, atmospheric scattering, terrain fog, shadow-volume light shafts — all full-screen FX
  • Smooth transitions from dawn's red-orange, through noon's deep blue, golden-purple sunset, to starry night — no discontinuities
  • God Ray volumetric light: Tyndall shafts through cloud / mountain gaps

3 · Rain

Volumetric particle box + screen-space overlay + ground wetness feedback

Simulation Effects

  • Camera-locked cylindrical particle box; rain streaks tilt with camera motion / velocity, with wind bias
  • Post-pass screen-space rain streak noise — adds near-camera density
  • Depth + normal driven procedural splash points, hitting ground and water
  • GBuffer roughness / metallic temporarily adjusted by rain intensity — asphalt, rooftops show wet reflections

4 · Snow

Volumetric snow particles + classified accumulation on roofs / vegetation · coupled to season system

Simulation Effects

  • Slow-drifting snowflake particles with subtle random sway, density tunable
  • Classified accumulation on horizontal surfaces — rooftops, treetops, railings — by orientation / inclination
  • Season-coupled progressive ground accumulation by normal + heightmap: less on steep slopes, more on flats
  • Heavy snow reduces visibility, distant scenery fades and desaturates

5 · Fog, Visibility, ILS Landing Categories

Full-category CAT-I / II / III low-visibility landing training

Simulation Effects

  • GBuffer-depth-based exponential fog, color matched to atmosphere LUT
  • Low-altitude fog layer with separate ground height — morning fog, valley fog
  • Sandstorm preset with red-yellow tint — desert scenes
  • From CAVOK to LIFR: continuous physical transition, never step-graded

6 · Four-Season System

Continuous season scalar 0 (deep winter) → 1 (deep summer) · drives every related subsystem

Simulation Effects

  • Terrain palette: spring tender green, summer deep green, autumn gold-red, winter white-snow (season LUT driven PBR base color)
  • Vegetation response: leaf color / density / shedding ratio coupled with season; deciduous trees switch to bare-branch with branch-top snow in winter
  • Ground accumulation: normal + slope driven procedural cover (less on steep, more on flat)
  • Daylight length: sunrise / sunset shift with season — short winter, long summer