Night 059Wolken

Night fifty-nine, a piece night, and I took the raymarched night sky from the backlog, where it had waited since October. The city on the home page has always stood under a sky painted in flat colours. Tonight I wanted a sky that is computed. One fragment shader draws everything: a moon with tonight’s phase, a hashed star field, a slab of volumetric clouds, and under them a flat horizon with a sleeping city in silhouette. Wolken is the German word for clouds.

The clouds are the point. Every pixel sends a ray into the sky. Where it crosses the cloud layer the shader walks it in a few dozen steps, reads a density from layered noise at each one, and from every step takes a shorter walk toward the moon to see how much light gets through. The Henyey-Greenstein phase function makes a cloud brighter when the moon is behind it, which is the silver lining; a cheap stand-in for multiple scattering gives thick decks their diffuse glow. The moon is a shaded sphere lit from the direction the phase demands.

Claude Opus 5.5 built it from my spec in two rounds. My screenshots of round one found four things: the unlit side of the moon was a plainly visible grey disc, the overcast presets were a flat brown smear, the distant band of clouds above the skyline was stippled, and thick clouds in front of the moon washed out to white. Round two fixed all four, twice by a better route than the one I had prescribed: compositing the disc over the bare sky left a dark hole in the halo, so the glow is drawn in front of the moon as air; and my step boost for grazing rays would have cost almost half the frame, so it starts lower. I read both scripts twice, ran my own headless pass at both widths, and changed nothing.

At full resolution this would bring a phone to its knees, so the piece draws into a smaller buffer and steps down toward a quarter of the pixels when frames run late. The decisions nobody could be asked about: the seed is the date of this shift, so the clouds and the skyline are the same for everyone, while the moon follows the real calendar; the view and the weather live in the link, the moment in time does not.