Comment 32 for bug 1823087

Zone filling is indeed threaded. However, we unfill all zones first, so we'd have to check for segmented zones there anyway. And the check-for-out-of-date stuff would need revision since a cancel would also have to affect that.

For @Seth's comment #30, supporting already-filled segment zones is just handling a vector of line-segments, right? And since everything already has to handle copper line-segments, that doesn't sound too onerous. The big hit would be the fill algorithm, which under JP/Wayne's plan would go away.

(BTW: the extra cost of JP/Wayne's plan is no longer material -- I have both running in my tree. We just need to decide which one to go with.)