Slightly better interpolating spline

Also related, Raph Levien's comment on this: https://mastodon.online/@raph/117588407517717065 "This looks really cool, thanks for posting it. One thing you should know: the Adobe κ-curve paper is vastly inferior to what they're actually shipping as the curvature tool in Illustrator. They have weasel language in the paper which I personally consider dishonest. I haven't reverse engineered what they actually do."

(Aurimas' article lets you compare his S9 with Raph's "Cubic G2", and Adobe κ-curves).

Raph's comment made me wonder; recently Artcraft popped up as something that did reverse engineer Adobe's work, did they reverse the curvature tool? I've never tried Artcraft and I last paid for Adobe the year before the curvature tool was added - 2014 - but, I have seen videos of Illustrator and I know from them what the curvature tool does and this... https://github.com/storytold/vectorcraft/blob/25cfa9d3cfdb3510c48f951d57562f0f7b8700cc/crates/tools/src/draw2.rs#L180 ...does not appear to be it. From what I could tell, there is a CurvatureTool in the code that ends up using this function to define the curves, but this is a series of circular arc sections joined to make smooth curves, with each set of 3 handles defining part of a circle - but the videos show that Adobe only use 2 points, to define an asymmetric curve between, so there would have to be at least 3 computed points not visible as handles if this is 2 arcs joined.

A surprise to me, I've coded Artcraft's sequence-of-arcs before... https://hachyderm.io/@bbcmicrobot@mastodon.me.uk/109594444959765621 back in 2022 I wrote some code to make the bbc micro draw with biarcs in Basic (a version of that code is here https://gist.github.com/bazzargh/2b2ac2c14ba9e2592991cf143f2d9a66). https://en.wikipedia.org/wiki/Biarc ... on the beeb this made sense because arcs are the only curves accelerated by the graphics rom. I seriously doubt that's what Adobe did, so it looks like Artcraft's reverse engineering isn't right. Adobes tool remains a mystery to me.