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@remotion/paths: Treat arcs with a zero radius as straight lines - #12859
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JonnyBurger merged 1 commit intoNov 1, 2026
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The SVG spec draws an `A` command with `rx` or `ry` of 0 as a straight line to its end point. Every sampled point of such an arc was (0, 0), so `getLength()` returned 0, `getPointAtLength()` returned (0, 0) at the start and null after it, and `evolvePath()` returned a `0 0` dash array. Interpolate along the line instead, as the existing comment intended. Co-Authored-By: Claude Opus 5.5 <[email protected]>
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One-commit PR making construct() handle zero-radius arcs per the SVG spec ("Out-of-range elliptical arc parameters").
- Zero-radius arc fallback (
packages/paths/src/helpers/arc.ts) —pointOnEllipticalArc()now linearly interpolates betweenp0andp1(p0 + (p1 - p0) * t) instead of returning(0, 0). Becausetis the normalized arc-length fraction formakeArc(), this makesgetLength(),getPointAtLength(),getTangentAtLength()andevolvePath()agree withreduceInstructions()/getBoundingBox()/cutPath(), which already replace such arcs with a line. - Test (
packages/paths/src/test/get-point-at-length.test.ts) — covers the absolute (A) and relative (a) forms: length ≈ 50 and midpoint ≈ (30, 25) forM 10 10 A 0 20 0 0 1 50 40.
I verified the full packages/paths suite locally (107 pass, 0 fail) and confirmed makeArc is the only consumer of pointOnEllipticalArc, so no other behavior is affected.
deepseek-v4.1-flash ｜ 𝕏
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Per the SVG spec ("Out-of-range elliptical arc parameters"), an arc with
rx = 0orry = 0is a straight line to its end point.reduceInstructions()(and sogetBoundingBox()/cutPath()) already does that, butconstruct()didn't:pointOnEllipticalArc()returned(0, 0)for every sample, with the line case left as a commented-out TODO.For
M 10 10 A 0 20 0 0 1 50 40:getLength()getPointAtLength(p, 0)getPointAtLength(p, 25)evolvePath(0.5, p)0 0, offset 050 50, offset ≈25I used Claude Code to write this change.