light-rays

The pure half of light shafts (WEATHER-DESIGN stage 4, board #1084): when a shaft exists, how bright it is along its length and toward the sun, how it widens, and how sunlight bends entering water. No Babylon; b3d-light-shafts draws it, under the cloud deck and under the water with the SAME model.

The model (Tonio, 2026-09-27):

• A shaft STARTS at the edge the light comes through (the underside of the cloud, the underside of the water) and runs away from it along the light.
• It is an additive fill of the light's colour, flat across and NOT blurred: edge (0.35) at the source, falling linearly to 0 at its far end.
• It is RECTANGULAR by default (spread 0): parallel to the sun's light, so perspective alone makes a set of them radiate from the sun and widen toward you. spread adds real widening if wanted.
• It is most prominent looking TOWARD the sun: light scattered forward by the medium, a phase term on the angle between your view and the sun.
• Under cloud it only makes sense for a broken sky: coverage 0.5 or more, but not closed (1+). And the gaps set the width: broad shafts from the ragged sky at the threshold, very narrow ones as the cover closes toward 1.