moonShaft

The single shaft of moonlight that drops through the Codex Tower's lantern dome onto its reading floor, and the pool it lands in. One additive material on a cylinder and a disc.

The shaft is a volume, not a surface: each fragment solves the view ray against the cylinder and shades the chord of lit air the ray crossed, through Beer's law. That is where the defined silhouette and the correct through-the- middle brightness come from, and it is why the camera can walk into the beam.

Where the shaft stands changes every frame, so it arrives on the entity's own per-instance lanes rather than on the material — a material property is authored state, and writing one every frame writes a file every frame:

The material itself carries only what does not move: the tint, the pool's edge exponent, and the dust — grain, grain_scale and drift, the last being how fast the motes fall through the beam in metres a second.