CavalierContours: Why not defined normalizing for zero vector? You can do it.

auto lineVisitor = [&](PlineVertex<Real> const& v1, PlineVertex<Real> const& v2) { result.emplace_back(); PlineOffsetSegment<Real>& seg = result.back(); seg.collapsedArc = false; seg.origV2Pos = v2.pos(); Vector2<Real> edge = v2.pos() - v1.pos(); Vector2<Real> offsetV = offset * unitPerp(edge); seg.v1.pos() = v1.pos() + offsetV; seg.v1.bulge() = v1.bulge(); seg.v2.pos() = v2.pos() + offsetV; seg.v2.bulge() = v2.bulge(); };

v1 and v2 are same after offset. Then it says “normalize not defined for zero vector”