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Experiments with Euler spirals and error metrics #229

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This branch contains some experiments with Euler spirals, particularly trying to come up with error metrics that are cheap to evaluate. It's on top of the euler branch, which probably should be cleaned up and merged at some point. The commits up to 8c4fee represent merges and cleanup of the more generic Euler work.

Most of the work is in the "euler2" example. This needs the "euler" feature to compile. The main thing there is generation of a random cubic Bézier, then finding the Euler spiral (with geometric Hermite interpolation, thus G1 continuity) and trying to estimate the error between the two.

This branch is not intended for merge, but may contain some work that's useful.

raphlinus and others added 16 commits February 11, 2021 08:39
Checkpoint of experiment work
Adds derivatives and curvature.
Generate Euler spirals from cubics.
Iterate from Euler spirals to cubics, with an error tolerance.
Provide accuracy (with verified error bounds).
Add benchmarks and refine error estimation (the powf was potentially
expensive).
Rename "FitEulerResult" to "EulerParams".
Also make them easier to find and improve docs a bit.
A pretty good implementation of parallel curves, including handling the
cusp, and applying the closed-form error metric for subdivision.
This commit captures the source code for the illustrations in the
parallel curve blog post.
This is a sketch of "reverse curve fitting," more specifically figuring out an error metric for converting arbitrary cubic beziers to euler spirals. What's there is promising but not polished.
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