Unintuitive output for vsk.arc's start and stop params

[bcongdon]

I'm a bit confused by the "start" and "stop" parameters of vsk.arc. They don't seem to do what I'd expect:

self.ellipseMode("radius")
self.arc(0, 0, w=5, h=5, start=0, stop=90, degrees=True)
self.arc(15, 0, w=5, h=5, start=90, stop=180, degrees=True)
self.arc(30, 0, w=5, h=5, start=180, stop=270, degrees=True)
self.arc(45, 0, w=5, h=5, start=270, stop=360, degrees=True)
self.circle(60, 0, diameter=5)

With the above code, I'd expect the output to look more like this:

Put another way, it looks like the "start" and "stop" degrees are not always relative to the same absolute starting reference point. This same behavior seems to happen in radians mode too. Am I misunderstanding the intended usage?

[abey79]

vsketch uses the unit circle convention: zero angle points to the right and positive angles extend counter-clockwise. In this regards, the output of your code is as expected. You were instead expecting the "compass" conversion (0 angle pointing top, positive angles extending clockwise).

I will clarify the documentation on this.

[bcongdon]

Ah, I see. That makes a lot more sense now, thanks for the clarification!

[abey79]

No worries.

I'm going to reopen this issue so I don't forget to update arc's documentation.

[lenary]

This caught me out too, because the +y direction of the unit circle for arc and the +y direction for coordinates do not match, if you use vsk.size(…, landscape=True, center=False). In this case, Increasing y takes you "down" the page in coordinate space, whereas for your unit circle increasing y takes you "up" the page.

[abey79]

I agree this is not ideal. I should add this to the list of breaking changes to make pre-1.0.