Fix zero tangents at polyline endpoints in simplify_bezpath - #606
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mlwilkerson wants to merge 2 commits into
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Fix zero tangents at polyline endpoints in simplify_bezpath#606mlwilkerson wants to merge 2 commits into
mlwilkerson wants to merge 2 commits into
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Line segments converted via `to_cubic` have a derivative that vanishes at t = 0 and t = 1, so `SimplifyBezPath::sample_pt_tangent` returned the zero vector at run endpoints. `fit_to_cubic` then took `atan2(0, 0) == 0`, silently constraining the fit to the world +x axis and producing degenerate or reversed end tangents (hairpins past the endpoint). Fall back to the cubic's chord when the sampled derivative is zero; the chord is the exact tangent for the line-segment case, the only way these non-regular cubics arise here. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Closes #605
Claude's fix here and Claude's description follows:
SimplifyBezPath::sample_pt_tangentreturned the zero vector at the endpoints of line segments (theirto_cubicformhas a vanishing derivative at
t = 0andt = 1), whichfit_to_cubicturned into a spurious +x-axis tangentconstraint via
atan2(0, 0). Fall back to the cubic's chord when the sampled derivative is zero — exact for theline-segment case, the only way these degenerate cubics arise here.
Adds a regression test: a quarter-circle polyline now fits with correct end tangents (as a single cubic) instead of a
hairpin.