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Fix SSurface::EdgeNormalsWithinSurface() to handle non-orthogonal u,v derivatives correctly.

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This commit is contained in:
phkahler 2020-06-01 21:10:25 -04:00 committed by whitequark
parent 225f82a292
commit 94a3cfdeb7
1 changed files with 9 additions and 3 deletions
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12
src/srf/boolean.cpp
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@ -379,11 +379,17 @@ void SSurface::EdgeNormalsWithinSurface(Point2d auv, Point2d buv,
enxyz = (ab.Cross(*surfn)).WithMagnitude(SS.ChordTolMm());
// And based on that, compute the edge's inner normal in uv space. This
// vector is perpendicular to the edge in xyz, but not necessarily in uv.
Vector tu, tv;
Vector tu, tv, tx, ty;
TangentsAt(muv.x, muv.y, &tu, &tv);
Vector n = tu.Cross(tv);
// since tu and tv may not be orthogonal, use y in place of v, x in place of u.
// |y| = |v|sin(theta) where theta is the angle between tu and tv.
ty = n.Cross(tu).ScaledBy(1.0/tu.MagSquared());
tx = tv.Cross(n).ScaledBy(1.0/tv.MagSquared());
Point2d enuv;
enuv.x = enxyz.Dot(tu) / tu.MagSquared();
enuv.y = enxyz.Dot(tv) / tv.MagSquared();
enuv.x = enxyz.Dot(tx) / tx.MagSquared();
enuv.y = enxyz.Dot(ty) / ty.MagSquared();
// Compute the inner and outer normals of this edge (within the srf),
// in xyz space. These are not necessarily antiparallel, if the