Further extensions to make this an uber tool:

There needs to be a 'convert to path' dynamic tool, which maintains a path converted from the original shape (spiral, oval etc) so that the user can edit the handles on the original shape.

That is, a spiral can be the parent of a path, and the path, the parent of an offset - so the spiral can affect the offset without becoming a path? That might be cool indeed.

Rather than defaulting to 'cap', outset should allow the user to choose between the 3 corner choices, cap, mitre and bevel.

Simply use the cap/join settings of the shape being offset

Why does the path always get closed? I can't see any justification for this in the algorithm?

Agreed

Why does a crossed (self intersecting) path get 'unwound' when making outset? I would have thought that a reasonable definition would be 'the curve n pixels to the left of this curve as I walk in the standard direction'. This would remove some of the abiguity I think?

Intuitively, when I have a shape with a hole, I expect outset to close this hole and inset to make it bigger. This is what the current algorithm does.

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