Arc.Polyline doesn't work if its domain has negative length. about elements HOT 2 CLOSED

There is a third option.
When a decreasing angle is provided, we should flip the basis circle (e.g. -Z normal) and make the angle increasing (but preserve the user's thought about "start" "end" in the parameterization — IOW, second parameter angle corresponds to "end", always.)

So:
in Arc constructors, if the user supplies a decreasing angle range, flip the order to be increasing and flip the basis curve direction to preserve the user's intended direction

Resulting behavior should follow this diagram.

@andrewheumann is the real expert though, and should review the solution. :)

from elements.

After some tries, it's not possible to implement what is shown because Arc parameter space is not 0 => Length but tied to the circle: first one is 0 to pi/2, second is 0 to -pi/2 or indeed 0 to pi/2 if normal is reversed. But third one is pi/2 to 0 in original direction or 3pi/2 to 2pi in reverse. Flipping Z or Transform is also have side effect of flipping X or Y axis as well to preserve correct hand rule I think this is too confusing.
It's either consistent domain and simple maintenance or more flexibility but some risks.
I did a PR with support of negative domain and fixes for Arc functions that were not consistent: #998

from elements.