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Classify a tangent face that meets our surface edge-on beside a crossing face. Fixes the tangent-outside case from #1291 #5

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Classify a tangent face that meets our surface edge-on beside a crossing face. Fixes the tangent-outside case from #1291 #5

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ced9b09
Classify a tangent face that meets our surface edge-on beside a cross…
BoykoNeov Jul 27, 2026
b56bacb
Add a regression test for Booleans with a face tangent beside a cross…
BoykoNeov Jul 27, 2026
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89 changes: 67 additions & 22 deletions src/srf/raycast.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -425,6 +425,40 @@ SShell::Class SShell::ClassifyRegion(Vector edge_n, Vector inter_surf_n,
// use overlapping sets of 3 to reduce memory usage.
static const double Random[8] = {1.278, 5.0103, 9.427, -2.331, 7.13, 2.954, 5.034, -4.777};

//-----------------------------------------------------------------------------
// A face of our shell meets the surface being classified edge-on, with its
// normal parallel to that surface's normal at p, so the face lies in that
// surface's tangent plane at p. It might be coincident with the surface there,
// or it might merely be tangent to it at the shell's edge and curve away from
// it past that edge. The normals at p can't tell those apart, so probe the
// face's actual geometry a little way in from the shell's edge, and report how
// far it then deviates from the tangent plane (measured along nu, a unit
// normal to the surface at p). The direction we probed in, which points into
// the face perpendicular to the shell's edge, is returned in f.
//-----------------------------------------------------------------------------
static double ProbeTangentFace(SSurface *srf, Vector p, Vector inter_edge_n,
Vector nu, Vector *f, bool *flat)
{
// Probe at a small fraction of the face's own size, so that the deviation
// of a curved face is well above numerical noise no matter the model's
// scale.
Vector c00 = srf->ctrl[0][0],
cm0 = srf->ctrl[srf->degm][0],
c0n = srf->ctrl[0][srf->degn],
cmn = srf->ctrl[srf->degm][srf->degn];
double size = max(max((cm0.Minus(c00)).Magnitude(),
(c0n.Minus(c00)).Magnitude()),
(cmn.Minus(c00)).Magnitude());
// inter_edge_n points out of the face, so negate it to probe into it.
*f = (inter_edge_n.ScaledBy(-1)).WithMagnitude(max(size / 20, LENGTH_EPS * 100));

Point2d fuv;
srf->ClosestPointTo(p.Plus(*f), &fuv, /*mustConverge=*/false);
double dev = ((srf->PointAt(fuv)).Minus(p)).Dot(nu);
*flat = fabs(dev) < max(LENGTH_EPS, 1e-3 * f->Magnitude());
return dev;
}

bool SShell::ClassifyEdge(Class *indir, Class *outdir,
Vector ea, Vector eb,
Vector p,
Expand Down Expand Up @@ -479,7 +513,33 @@ bool SShell::ClassifyEdge(Class *indir, Class *outdir,
swap(inter_srf[0], inter_srf[1]);
}

Class coinc = (surf_n.Dot(inter_surf_n[0])) > 0 ? Class::SURF_COINC_SAME : Class::SURF_COINC_OPP;
// The class of the side of our edge that face 0 extends into, when
// face 0 lies in our tangent plane at p and face 1 does not. That's
// coincident with the shell if face 0 really is coincident with our
// surface, but see below for when it's only tangent to it.
Class towards_0 =
(surf_n.Dot(inter_surf_n[0])) > 0 ? Class::SURF_COINC_SAME : Class::SURF_COINC_OPP;

if(fabs(dotp[0]) < DOTP_TOL && fabs(dotp[1]) >= DOTP_TOL) {
// Face 0 might be merely tangent to our surface at the shell's
// edge, curving away from it past that edge, e.g. where the
// spline face of a cut is tangent to the face it cuts through
// and the cut's other face crosses that face there (issue
// #1291). Then the side of our edge towards face 0 is not
// coincident with the shell at all; it's inside or outside it
// depending on which way face 0 curves away.
Vector f;
bool flat;
double dev = ProbeTangentFace(inter_srf[0], p, inter_edge_n[0],
surf_n.WithMagnitude(1), &f, &flat);
if(!flat) {
// As in the both-tangent case below: our edge is on the
// shell's material side of face 0 iff face 0 curves away
// opposite its own outward normal.
towards_0 = (dev * surf_n.Dot(inter_surf_n[0]) > 0) ?
Class::SURF_INSIDE : Class::SURF_OUTSIDE;
}
}

if(fabs(dotp[0]) < DOTP_TOL && fabs(dotp[1]) < DOTP_TOL) {
// Both faces meeting at the shell's edge lie in our surface's
Expand All @@ -498,23 +558,8 @@ bool SShell::ClassifyEdge(Class *indir, Class *outdir,
bool flat[2]; // does face i lie in our tangent plane?
Vector nu = surf_n.WithMagnitude(1);
for(int i = 0; i < 2; i++) {
// Probe at a small fraction of the face's own size, so
// that the deviation of a curved face is well above
// numerical noise no matter the model's scale.
SSurface *srf = inter_srf[i];
Vector c00 = srf->ctrl[0][0],
cm0 = srf->ctrl[srf->degm][0],
c0n = srf->ctrl[0][srf->degn],
cmn = srf->ctrl[srf->degm][srf->degn];
double size = max(max((cm0.Minus(c00)).Magnitude(),
(c0n.Minus(c00)).Magnitude()),
(cmn.Minus(c00)).Magnitude());
f[i] = (inter_edge_n[i].ScaledBy(-1))
.WithMagnitude(max(size / 20, LENGTH_EPS * 100));
Point2d fuv;
srf->ClosestPointTo(p.Plus(f[i]), &fuv, /*mustConverge=*/false);
dev[i] = ((srf->PointAt(fuv)).Minus(p)).Dot(nu);
flat[i] = fabs(dev[i]) < max(LENGTH_EPS, 1e-3 * f[i].Magnitude());
dev[i] = ProbeTangentFace(inter_srf[i], p, inter_edge_n[i], nu,
&f[i], &flat[i]);
}
Class *dir[2] = { indir, outdir };
Vector en[2] = { edge_n_in, edge_n_out };
Expand Down Expand Up @@ -555,19 +600,19 @@ bool SShell::ClassifyEdge(Class *indir, Class *outdir,
}
} else if(fabs(dotp[0]) < DOTP_TOL && dotp[1] > DOTP_TOL) {
if(edge_n_out.Dot(inter_edge_n[0]) > 0) {
*indir = coinc;
*indir = towards_0;
*outdir = Class::SURF_OUTSIDE;
} else {
*indir = Class::SURF_INSIDE;
*outdir = coinc;
*outdir = towards_0;
}
} else if(fabs(dotp[0]) < DOTP_TOL && dotp[1] < -DOTP_TOL) {
if(edge_n_out.Dot(inter_edge_n[0]) > 0) {
*indir = coinc;
*indir = towards_0;
*outdir = Class::SURF_INSIDE;
} else {
*indir = Class::SURF_OUTSIDE;
*outdir = coinc;
*outdir = towards_0;
}
} else if(dotp[0] > DOTP_TOL && dotp[1] > DOTP_TOL) {
*indir = Class::SURF_INSIDE;
Expand Down
1 change: 1 addition & 0 deletions test/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,7 @@ set(testsuite_SOURCES
request/workplane/test.cpp
group/boolean_coplanar_union/test.cpp
group/boolean_knife_edge/test.cpp
group/boolean_tangent_crossing/test.cpp
group/boolean_tangent_edge/test.cpp
group/boolean_tangent_fillet/test.cpp
group/boolean_tangent_spline/test.cpp
Expand Down
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