🚀 What's New in v1.2.0 — Physical Clouds

Version 1.2.0 is the first release of the physical cloud line. The cloud deck stops being four painted sheets and becomes a medium with a droplet spectrum; the atmosphere coefficients are re-derived from measured column depths; godrays integrate a filtered transmittance with a fixed step count; the colour stage becomes twelve sliders;

☁️ Volumetric Cloud Engine — Microphysics, Not Constants

• The deck is a medium. CLOUD_DENSITY selects a liquid water content (0.075 / 0.15 / 0.30 g/m³) and CLOUD_MICRO a droplet spectrum (Continental 6 µm / Typical 8 µm / Maritime 12 µm); extinction is derived from them (σ = 3·LWC·Q_ext / 4ρ·r_eff), so "dense" is a physical quantity rather than a number that was tuned by eye.
• Resolution and detail are independent. CLOUD_QUALITY is the raymarch budget (Cheap 14 / Standard 24 / High 36 / Extreme 56 steps) and the new CLOUD_DETAIL is the shape field (2–5 octaves, 1080 → 135 m features). A weak GPU can keep crisp cloud tops and drop the step count instead of the shape; the two multiply, and the cost table is in the release notes.
• Coverage is cloud fraction, not brightness. New CLOUD_COVERAGE (Clear / Scattered / Broken / Broken to overcast / Overcast) moves the threshold the shape field has to cross, and each octave preset carries a bisected offset so "Broken" covers the same ~40 % of the sky on every profile.
• Cirrus is ice, not a small cumulus. New CLOUD_CIRRUS marches a fibrous veil at 6.5–11.2 km with its own extinction (~0.09 g/m³, 25 µm), and it dissolves into the horizon haze instead of ending on a visible edge.
• An independent mid-level deck. New CLOUD_MID_LAYER adds a second, separate layer rather than repeating the cumulus field.
• Real air. Altitudes in metres via CLOUD_HEIGHT (400 m / 1200 m / 2400 m / 3600 m), deck depth as a fraction of the base altitude, reach out to 32 km, wind as a velocity in m/s, per-cloud condensation level (CLOUD_BASE_VARIATION) and vertical development (CLOUD_UPDRAFT), and multiple scattering instead of a single-sample light tap.
• CLOUD_MODE keeps the v1.1.4 layered sheets available (Layered sheets / Volumetric) for hardware that cannot afford the march.

🌤️ Godrays — Filtered, Bounded and Stable in Time

• Shafts sample a filtered shadow term — a smoothstep band expressed in the same space as the depth compare — instead of step() on the blocker depth. Moving the camera by a fraction of a shadow texel no longer flips whole samples between lit and unlit.
• Fixed step count. The path is bounded (40 km) and divided into a constant number of taps, so the optical depth changes continuously as the sun moves instead of jumping whenever the path crosses a multiple of the old 150 m step.
• One cloud-shadow column per frame. The cloud transmittance that gates the shafts is screen-independent, so it is evaluated once per fullscreen-quad vertex in composite.vsh and handed over as a flat varying — 4 evaluations per frame instead of 2 million. That file is generated from composite.fsh by tools/gen_composite_vsh.py, so the duplicated field code cannot drift; CI can verify it with --check.
• Near-horizontal light fades out towards the horizon instead of integrating an effectively infinite path through the deck, which is what made the shafts "breathe" at sunset.

🌇 Atmosphere — Coefficients From Measurements, Twilight From Optics

• Rayleigh, aerosol scattering and absorption, and ozone as a 25 ± 15 km tent (Bruneton/Hillaire) replace the hand-tuned triplet that carried roughly 9× too much aerosol and no ozone at all.
• Twilight is produced by the optical path: civil, nautical and astronomical phases, the Earth's shadow and the Belt of Venus, all in gbuffers_skybasic. The old global on/off ramp over the finished result is gone, so the sky no longer dies by solar −1.4°.
• Airglow is added after the dark-adaptation gain. Multiplying it by the gain (which reaches 28 in deep twilight) used to paint the entire night

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