drains

Whether a surface has a drainage graph at all — the one thing about the graph that can be answered without building one.

build is fifty to a hundred milliseconds, and the callers that only need "is there one" run on the thread that draws: the streamer asks once a patch whether the sheet comes from the field or from a datum. Asking drainageGraph there is a frame of stall the first time a wet body is streamed on a build that never otherwise needs the graph on this thread.

surfaceSurfaceParameters

Undocumented