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Mate connectors: derive a face-only frame's X from the face, not from world

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datum_frame took a FaceAndDirection frame's Z from the face normal, which
follows the body, but its X from coordsys_x_hint, a world constant, whenever
no explicit edge reference was set. Spinning a body about its own face normal
therefore left the frame bit-identical: the connector could not encode that
rotation at all, so Fastened and Slider mates claimed to fix an orientation
the frame could not see.

X now comes from the face's own first usable edge, which rotates with the
body. The hint survives only as a last resort, for faces that offer no
in-plane direction — a full circular edge has coincident endpoints, and a
seam projects to nothing in-plane.

The new test spins a box 90 degrees about its top-face normal and asserts the
frame's X turned with it. Reverting just the X_tent derivation and rerunning
makes it fail with "1.0 is within 0.000001 of 0.0" — cos(angle) between the
before and after X is exactly 1, i.e. the frame did not move — and that is the
only failure in 2019 assertions, so the test discriminates this defect and
nothing else.

Note for anyone replaying an older document: a face-only connector's frame
can now differ from what that recipe produced before, so a mate built on one
may place its body differently. Nothing in the suite or the golden v3 fixture
changed, but the semantics did.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Tommaso Bianchi
2026-07-26 08:18:42 +02:00
co-authored by Claude Opus 5
parent f13f2876f6
commit 1726e93760
2 changed files with 78 additions and 2 deletions
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src/libslic3r/CadDocument.cpp
+23 -2
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@@ -1681,8 +1681,29 @@ CadDocument::DatumCoordSys CadDocument::datum_frame(const std::vector<CadBody>&
if (fc.IsNull()) { ds.error = "face not found"; break; }
ds.origin = GeometryEngine::face_centroid_world(fc);
Vec3d Z = GeometryEngine::face_normal_world(fc);
// Tentative X: edge direction if available, else the hint or a fallback.
Vec3d X_tent = have_edge ? edge_dir : f.coordsys_x_hint;
// Tentative X: an explicit edge reference wins. Failing that, derive X from the
// face's OWN first usable edge, so the frame rotates with the body. Reading it from
// coordsys_x_hint — a world constant — meant a face-only connector could not encode
// spin about its own normal: Z followed the body, X did not, so Fastened and Slider
// claimed to fix an orientation the frame could not see. The hint survives only as a
// last resort, for faces that offer no usable direction (a full circular edge has
// coincident endpoints, and a cylinder's seam projects to nothing in-plane).
Vec3d X_tent = Vec3d::Zero();
if (have_edge) {
X_tent = edge_dir;
} else {
for (const TopoDS_Edge& fe : GeometryEngine::edges_of_face(fc)) {
auto pts = GeometryEngine::sample_edge_world(fe);
if (pts.size() < 2) continue;
Vec3d d = pts.back() - pts.front();
if (d.squaredNorm() < 1e-18) continue; // closed edge: endpoints coincide
Vec3d in_plane = d - Z * Z.dot(d); // drop any out-of-plane component
if (in_plane.squaredNorm() < 1e-18) continue;
X_tent = in_plane;
break;
}
if (X_tent.squaredNorm() < 1e-18) X_tent = f.coordsys_x_hint;
}
if (X_tent.squaredNorm() < 1e-18) { ds.error = "zero-length direction"; break; }
X_tent.normalize();
// Gram-Schmidt: ensure orthonormal, right-handed frame.