noon_shaft

A bar of sunlight standing in the air between two columns. The material draws on a box of air; the fragment marches the view ray through that box and asks at each sample whether a ray toward the sun clears the colonnade — an analytic test against the column line, the stylobate under it and the architrave over it, so the bar carries the colonnade's own edges rather than a shadow map's. Scatter runs through a Henyey-Greenstein lobe, so the same air is bright looking into the sun and nearly clear looking away from it.

The sun comes from the frame, so the bars swing, lengthen and change colour with the day cycle without being told. Instance lane 0 carries the box centre and this slab's intensity; lane 1 the x of the column line it stands beside.