trailHalfLifeAt

How long the trail takes to fade to half, in seconds, for this mood.

A drawing declares its trail as the share of the picture that survives one sixtieth of a second, which is how it was authored. This is the same number as a time, which is what the surface fades by, so a drawing fades at the same rate on any refresh rate. Most drawings sit between 50 and 250 ms; the ones built to look like a long exposure sit above that on purpose.