handle self-intersecting paths in convert to satin

[lexelby]

This one's bothered me since I wrote Convert to Satin. This version automatically detects paths that loop back on themselves and splits them up. No more telling the user to split up the path, now Ink/Stitch does it for them, splitting as many times as necessary to make it work.

The code isn't brilliant, but it seems to get the job done. It just repeatedly splits the path in half until it finds pieces that don't self-intersect, then converts each to a satin by itself. This means that if you convert a path you might end up with multiple satins, but they're in order so it's really not that big a deal. Maybe in the future we can try to join the satins up, but I don't think it's going to matter all that much to the user.

[kaalleen]

I don't know if this is ready for testing, but since I was at the computer I thought I'd give it a try.
It works great, but if users go a bit too crazy about it, we get an error message:

[...] inkstitch/lib/extensions/convert_to_satin.py", line 167, in get_scores
    angle = abs(math.degrees(math.acos(cos_angle_between)))
ValueError: math domain error

Tested with this file

If the shape is simplified through Ctrl+L everything works fine.

[lexelby]

Yup, definitely ready for testing, same for the other two PRs I made last week.

Nice find, awesome work! I think that problem must have existed since we added Convert To Satin in the first place :)

[lexelby]

Speaking of going crazy, there are some edge cases where this new version still doesn't work, like if a path doubles back on itself sharply at the end. I'm okay with that though, because the user can pretty easily see how to fix it. Garbage in, garbage out. :)

[kaalleen]

Speaking of going crazy, there are some edge cases where this new version still doesn't work, like if a path doubles back on itself sharply at the end. I'm okay with that though, because the user can pretty easily see how to fix it. Garbage in, garbage out. :)

You are reading my mind ;)
I was just going to add a similar comment about this issue right here.
Sharp edges shouldn't be the way you design a satin column and we are giving a proper error message already now. If the user doesn't see it right away, you can still use the troubleshoot extension, which will point directly to the bad rung (... or let's better say bad edge).

[lexelby]

I found a separate error. I tried it on a path and got a "recursion depth exceeded" error. I knew that was a risk, and, well, here we are. :) The path had a really gnarly little tangle at one of the corners, created by using "stroke to path". I cleaned it up and it worked fine. Now to figure out how to automate that cleanup...