Enum LinesMode 

pub enum LinesMode<'a> {
    Compute,
    Defer(&'a mut dyn FnMut(LinesJob) -> Deferred),
}

What a projection does on an exact-lines MISS.

Variants

Compute

Run the pass here and now, on this thread — an export, a test, a runner that cannot run the job.

Defer(&'a mut dyn FnMut(LinesJob) -> Deferred)

Hand the job over. The answer comes back as the lines (a runner that answered at once), None while it is being computed elsewhere — the placement then draws its mesh approximation — or Deferred::Here to run it on this thread after all.