G4OCCTSolid.cc

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// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2026 G4OCCT Contributors
 
 
#include "G4OCCT/G4OCCTSolid.hh"
 
#include <BRepAdaptor_Curve.hxx>
#include <BRepAdaptor_Surface.hxx>
#include <BRepBndLib.hxx>
#include <BRepClass3d_SolidClassifier.hxx>
#include <BRepExtrema_DistShapeShape.hxx>
#include <BRepExtrema_SupportType.hxx>
#include <BRepExtrema_TriangleSet.hxx>
#include <BRepGProp.hxx>
#include <BRepLib.hxx>
#include <BRepLProp_SLProps.hxx>
#include <BRepMesh_IncrementalMesh.hxx>
#include <BRep_Builder.hxx>
#include <BRep_Tool.hxx>
#include <BRepTools.hxx>
#include <BRepTools_WireExplorer.hxx>
#include <BVH_Distance.hxx>
#include <BVH_Tools.hxx>
#include <Bnd_Box.hxx>
#include <ElSLib.hxx>
#include <GeomAbs_CurveType.hxx>
#include <GeomAbs_SurfaceType.hxx>
#include <GProp_GProps.hxx>
#include <GeomAPI_ProjectPointOnSurf.hxx>
#include <Geom_Surface.hxx>
#include <IFSelect_ReturnStatus.hxx>
#include <IntCurvesFace_Intersector.hxx>
#include <Poly_Triangulation.hxx>
#include <Precision.hxx>
#include <STEPControl_Reader.hxx>
#include <TopAbs_Orientation.hxx>
#include <TopAbs_ShapeEnum.hxx>
#include <TopAbs_State.hxx>
#include <TopExp_Explorer.hxx>
#include <TopLoc_Location.hxx>
#include <TopoDS.hxx>
#include <TopoDS_Edge.hxx>
#include <TopoDS_Face.hxx>
#include <TopoDS_Vertex.hxx>
#include <TopoDS_Wire.hxx>
#include <gp_Dir.hxx>
#include <gp_Lin.hxx>
#include <gp_Pln.hxx>
#include <gp_Pnt.hxx>
#include <gp_Pnt2d.hxx>
#include <gp_Vec.hxx>
 
#include <G4BoundingEnvelope.hh>
#include <G4AffineTransform.hh>
#include <G4Exception.hh>
#include <G4GeometryTolerance.hh>
#include <G4Polyhedron.hh>
#include <G4TessellatedSolid.hh>
#include <G4TriangularFacet.hh>
#include <G4VGraphicsScene.hh>
#include <G4VisExtent.hh>
#include <Randomize.hh>
 
#include <algorithm>
#include <cmath>
#include <optional>
#include <stdexcept>
#include <string>
#include <utility>
 
namespace {
 
constexpr Standard_Real kRelativeDeflection = 0.01;
 
class PointToMeshDistance
    : public BVH_Distance<Standard_Real, 3, BVH_Vec3d, BRepExtrema_TriangleSet> {
public:
  Standard_Boolean RejectNode(const BVH_Vec3d& theCornerMin, const BVH_Vec3d& theCornerMax,
                              Standard_Real& theMetric) const override {
    theMetric =
        BVH_Tools<Standard_Real, 3>::PointBoxSquareDistance(myObject, theCornerMin, theCornerMax);
    return RejectMetric(theMetric);
  }
 
  Standard_Boolean Accept(const Standard_Integer theIndex, const Standard_Real&) override {
    BVH_Vec3d v0, v1, v2;
    myBVHSet->GetVertices(theIndex, v0, v1, v2);
    const Standard_Real sq =
        BVH_Tools<Standard_Real, 3>::PointTriangleSquareDistance(myObject, v0, v1, v2);
    if (sq < myDistance) {
      myDistance  = sq;
      myBestIndex = theIndex;
      return Standard_True;
    }
    return Standard_False;
  }
 
  Standard_Integer BestIndex() const { return myBestIndex; }
 
private:
  Standard_Integer myBestIndex{-1};
};
 
class TriangleRayCast
    : public BVH_Traverse<Standard_Real, 3, BRepExtrema_TriangleSet, Standard_Real> {
public:
  void SetRay(const BVH_Vec3d& theOrigin, const BVH_Vec3d& theDir, Standard_Real theTolerance) {
    myOrigin    = theOrigin;
    myDir       = theDir;
    myTolerance = theTolerance;
 
    // Reset traversal output state so each cast starts from a clean state.
    myCrossings  = 0;
    myOnSurface  = Standard_False;
    myDegenerate = Standard_False;
  }
 
  Standard_Boolean RejectNode(const BVH_Vec3d& theCornerMin, const BVH_Vec3d& theCornerMax,
                              Standard_Real& theMetric) const override {
    Standard_Real tmin = 0.0;
    Standard_Real tmax = Precision::Infinite();
    for (int k = 0; k < 3; ++k) {
      const Standard_Real dk     = (k == 0) ? myDir.x() : (k == 1) ? myDir.y() : myDir.z();
      const Standard_Real ok     = (k == 0) ? myOrigin.x() : (k == 1) ? myOrigin.y() : myOrigin.z();
      const Standard_Real ck_min = (k == 0)   ? theCornerMin.x()
                                   : (k == 1) ? theCornerMin.y()
                                              : theCornerMin.z();
      const Standard_Real ck_max = (k == 0)   ? theCornerMax.x()
                                   : (k == 1) ? theCornerMax.y()
                                              : theCornerMax.z();
      if (std::abs(dk) < Precision::Confusion()) {
        if (ok < ck_min - myTolerance || ok > ck_max + myTolerance) {
          return Standard_True;
        }
      } else {
        Standard_Real t1 = (ck_min - ok) / dk;
        Standard_Real t2 = (ck_max - ok) / dk;
        if (t1 > t2) {
          std::swap(t1, t2);
        }
        if (t1 > tmin) {
          tmin = t1;
        }
        if (t2 < tmax) {
          tmax = t2;
        }
        if (tmin > tmax + myTolerance) {
          return Standard_True;
        }
      }
    }
    theMetric = tmin;
    return Standard_False;
  }
 
  Standard_Boolean Accept(const Standard_Integer theIndex, const Standard_Real&) override {
    BVH_Vec3d v0, v1, v2;
    myBVHSet->GetVertices(theIndex, v0, v1, v2);
    const BVH_Vec3d edge1 = v1 - v0;
    const BVH_Vec3d edge2 = v2 - v0;
    const BVH_Vec3d h     = BVH_Vec3d::Cross(myDir, edge2);
    const Standard_Real a = edge1.Dot(h);
    if (std::abs(a) < 1e-12) {
      return Standard_False; // ray parallel to triangle plane
    }
    const Standard_Real f = 1.0 / a;
    const BVH_Vec3d s     = myOrigin - v0;
    const Standard_Real u = f * s.Dot(h);
    if (u < 0.0 || u > 1.0) {
      return Standard_False;
    }
    const BVH_Vec3d q     = BVH_Vec3d::Cross(s, edge1);
    const Standard_Real v = f * myDir.Dot(q);
    if (v < 0.0 || u + v > 1.0) {
      return Standard_False;
    }
    const Standard_Real t = f * edge2.Dot(q);
    if (std::abs(t) <= myTolerance) {
      myOnSurface = Standard_True; // ray origin lies on this triangle
      return Standard_True;
    }
    if (t < -myTolerance) {
      return Standard_False; // triangle is behind the ray origin
    }
    // Forward crossing at t > myTolerance.
    ++myCrossings;
    // Proximity to an edge or vertex signals a potentially degenerate parity count.
    constexpr Standard_Real kEdgeTol = 1e-6;
    if (u < kEdgeTol || v < kEdgeTol || (1.0 - u - v) < kEdgeTol) {
      myDegenerate = Standard_True;
    }
    return Standard_True;
  }
 
  Standard_Boolean RejectMetric(const Standard_Real&) const override { return Standard_False; }
 
  Standard_Boolean Stop() const override { return Standard_False; }
 
  int Crossings() const { return myCrossings; }
  Standard_Boolean OnSurface() const { return myOnSurface; }
  Standard_Boolean Degenerate() const { return myDegenerate; }
 
private:
  BVH_Vec3d myOrigin;
  BVH_Vec3d myDir;
  Standard_Real myTolerance{1e-7};
  int myCrossings{0};
  Standard_Boolean myOnSurface{Standard_False};
  Standard_Boolean myDegenerate{Standard_False};
};
 
gp_Pnt ToPoint(const G4ThreeVector& point) { return gp_Pnt(point.x(), point.y(), point.z()); }
 
G4double IntersectionTolerance() {
  return 0.5 * G4GeometryTolerance::GetInstance()->GetSurfaceTolerance();
}
 
TopoDS_Vertex MakeVertex(const G4ThreeVector& point) {
  BRep_Builder builder;
  TopoDS_Vertex vertex;
  builder.MakeVertex(vertex, ToPoint(point), IntersectionTolerance());
  return vertex;
}
 
EInside ToG4Inside(const TopAbs_State state) {
  switch (state) {
  case TopAbs_IN:
    return kInside;
  case TopAbs_ON:
    return kSurface;
  case TopAbs_OUT:
  default:
    return kOutside;
  }
}
 
G4ThreeVector FallbackNormal() { return G4ThreeVector(0.0, 0.0, 1.0); }
 
bool PointInPolygon2d(Standard_Real u, Standard_Real v, const std::vector<gp_Pnt2d>& poly) {
  const std::size_t n = poly.size();
  int crossings       = 0;
  for (std::size_t i = 0; i < n; ++i) {
    const gp_Pnt2d& a      = poly[i];
    const gp_Pnt2d& b      = poly[(i + 1) % n];
    const Standard_Real av = a.Y();
    const Standard_Real bv = b.Y();
    if ((av <= v && bv > v) || (bv <= v && av > v)) {
      const Standard_Real uCross = a.X() + (v - av) * (b.X() - a.X()) / (bv - av);
      if (u < uCross) {
        ++crossings;
      }
    }
  }
  return (crossings % 2) == 1;
}
 
bool PointOnPolygonBoundary2d(Standard_Real u, Standard_Real v, const std::vector<gp_Pnt2d>& poly,
                              Standard_Real tol) {
  const Standard_Real tol2 = tol * tol;
  const std::size_t n      = poly.size();
  for (std::size_t i = 0; i < n; ++i) {
    const gp_Pnt2d& a        = poly[i];
    const gp_Pnt2d& b        = poly[(i + 1) % n];
    const Standard_Real dx   = b.X() - a.X();
    const Standard_Real dy   = b.Y() - a.Y();
    const Standard_Real len2 = dx * dx + dy * dy;
    Standard_Real px         = 0.0;
    Standard_Real py         = 0.0;
    if (len2 < 1.0e-20) {
      px = a.X();
      py = a.Y();
    } else {
      const Standard_Real t_seg =
          std::max(0.0, std::min(1.0, ((u - a.X()) * dx + (v - a.Y()) * dy) / len2));
      px = a.X() + t_seg * dx;
      py = a.Y() + t_seg * dy;
    }
    const Standard_Real dist2 = (u - px) * (u - px) + (v - py) * (v - py);
    if (dist2 <= tol2) {
      return true;
    }
  }
  return false;
}
 
std::optional<Standard_Real>
RayPlaneFaceHit(const gp_Lin& ray, const gp_Pln& plane, const std::vector<gp_Pnt2d>& uvPoly,
                Standard_Real tMin, Standard_Real tMax, Standard_Real tolerance,
                Standard_Real* u_out = nullptr, Standard_Real* v_out = nullptr) {
  const gp_Dir& lineDir   = ray.Direction();
  const gp_Dir& plnNormal = plane.Axis().Direction();
  const Standard_Real denom =
      plnNormal.X() * lineDir.X() + plnNormal.Y() * lineDir.Y() + plnNormal.Z() * lineDir.Z();
  // Ray parallel to the plane: no intersection (or entire ray lies on plane,
  // which we treat as no intersection for navigation purposes).
  if (std::abs(denom) < 1.0e-10) {
    return std::nullopt;
  }
  const gp_Pnt& orig        = ray.Location();
  const gp_Pnt& planePt     = plane.Location();
  const Standard_Real numer = plnNormal.X() * (planePt.X() - orig.X()) +
                              plnNormal.Y() * (planePt.Y() - orig.Y()) +
                              plnNormal.Z() * (planePt.Z() - orig.Z());
  const Standard_Real t     = numer / denom;
  if (t < tMin || t > tMax) {
    return std::nullopt;
  }
  const gp_Pnt hitPt(orig.X() + t * lineDir.X(), orig.Y() + t * lineDir.Y(),
                     orig.Z() + t * lineDir.Z());
  Standard_Real u = 0.0;
  Standard_Real v = 0.0;
  ElSLib::PlaneParameters(plane.Position(), hitPt, u, v);
  // Accept the hit when the UV point is strictly inside the polygon, or when it
  // lies within tolerance of any polygon edge (the TopAbs_ON-equivalent case).
  // Pure boundary-miss points that are strictly outside are rejected.
  if (!PointInPolygon2d(u, v, uvPoly) && !PointOnPolygonBoundary2d(u, v, uvPoly, tolerance)) {
    return std::nullopt;
  }
  if (u_out != nullptr) {
    *u_out = u;
  }
  if (v_out != nullptr) {
    *v_out = v;
  }
  return t;
}
 
std::optional<G4ThreeVector> TryGetOutwardNormal(const BRepAdaptor_Surface& surface,
                                                 const TopoDS_Face& face, const Standard_Real u,
                                                 const Standard_Real v) {
  Standard_Real adjustedU       = u;
  Standard_Real adjustedV       = v;
  const Standard_Real tolerance = IntersectionTolerance();
  // Nudge U away from parametric boundaries to avoid seam singularities.
  // For periodic surfaces this prevents descending into OCCT's 2D seam
  // classifier; for non-periodic surfaces with degenerate boundary edges
  // (e.g. the poles of a sphere) this ensures IsNormalDefined() returns true.
  {
    const Standard_Real uFirst   = surface.FirstUParameter();
    const Standard_Real uLast    = surface.LastUParameter();
    const Standard_Real uEpsilon = std::min(
        std::max(surface.UResolution(tolerance), Precision::PConfusion()), 0.5 * (uLast - uFirst));
    if (std::abs(adjustedU - uFirst) <= uEpsilon) {
      adjustedU = std::min(uFirst + uEpsilon, uLast);
    } else if (std::abs(adjustedU - uLast) <= uEpsilon) {
      adjustedU = std::max(uLast - uEpsilon, uFirst);
    }
  }
  // Nudge V away from parametric boundaries.  Non-periodic V boundaries
  // include degenerate pole edges on spheres (V = ±π/2) and cone apices.
  {
    const Standard_Real vFirst   = surface.FirstVParameter();
    const Standard_Real vLast    = surface.LastVParameter();
    const Standard_Real vEpsilon = std::min(
        std::max(surface.VResolution(tolerance), Precision::PConfusion()), 0.5 * (vLast - vFirst));
    if (std::abs(adjustedV - vFirst) <= vEpsilon) {
      adjustedV = std::min(vFirst + vEpsilon, vLast);
    } else if (std::abs(adjustedV - vLast) <= vEpsilon) {
      adjustedV = std::max(vLast - vEpsilon, vFirst);
    }
  }
 
  BRepLProp_SLProps props(surface, adjustedU, adjustedV, 1, tolerance);
  // If IsNormalDefined() fails the initial nudge may still be too small for
  // OCCT's internal null-derivative threshold (e.g. a sphere pole where
  // |dP/dU| = R·sin(δ) must exceed IntersectionTolerance()).  Retry with
  // exponentially larger V nudges, walking toward the V midpoint.
  if (!props.IsNormalDefined()) {
    const Standard_Real vFirst = surface.FirstVParameter();
    const Standard_Real vLast  = surface.LastVParameter();
    const Standard_Real vMid   = 0.5 * (vFirst + vLast);
    const bool nearVFirst      = (adjustedV < vMid);
    const Standard_Real vRes   = std::max(surface.VResolution(tolerance), Precision::PConfusion());
    Standard_Real finalRetryV  = adjustedV;
    for (int attempt = 0; attempt < 8 && !props.IsNormalDefined(); ++attempt) {
      const Standard_Real scale = std::pow(10.0, static_cast<Standard_Real>(attempt));
      const Standard_Real nudge = scale * vRes;
      finalRetryV =
          nearVFirst ? std::min(adjustedV + nudge, vMid) : std::max(adjustedV - nudge, vMid);
      props = BRepLProp_SLProps(surface, adjustedU, finalRetryV, 1, tolerance);
    }
    if (!props.IsNormalDefined()) {
      return std::nullopt;
    }
    // Guard: if the retry had to drift V by more than kMaxRetryVDriftFraction of
    // the full V range, the normal is sampled from a different surface region
    // (e.g. the equatorial band instead of the pole on a NURBS ellipsoid), which
    // would produce a spurious mismatch against the exact analytic normal, so we
    // treat the normal as unavailable at this point and return std::nullopt for
    // the caller to handle (e.g. by leaving the normal invalid or using a fallback).
    constexpr Standard_Real kMaxRetryVDriftFraction = 0.10;
    if (std::fabs(finalRetryV - adjustedV) > kMaxRetryVDriftFraction * (vLast - vFirst)) {
      return std::nullopt;
    }
  }
 
  gp_Dir faceNormal = props.Normal();
  if (face.Orientation() == TopAbs_REVERSED) {
    faceNormal.Reverse();
  }
 
  return G4ThreeVector(faceNormal.X(), faceNormal.Y(), faceNormal.Z());
}
 
} // namespace
 
G4OCCTSolid::G4OCCTSolid(const G4String& name, const TopoDS_Shape& shape)
    : G4VSolid(name), fShape(shape) {
  if (fShape.IsNull()) {
    throw std::invalid_argument("G4OCCTSolid: shape must not be null");
  }
  ComputeBounds();
}
 
G4OCCTSolid::~G4OCCTSolid() {
  // Manually clear cached OCCT objects to avoid G4Exception during static destruction.
  // G4Cache::Destroy() calls G4Exception with FatalException if cache size validation
  // fails, which can happen when G4SolidStore cleanup occurs during exit() and the
  // thread-local storage has already been torn down.
  // Resetting the optional values here releases the OCCT objects before G4Cache
  // attempts to destroy the thread-local storage.
  fClassifierCache.Get().classifier.reset();
  fIntersectorCache.Get().faceIntersectors.clear();
  fSphereCache.Get().spheres.clear();
}
 
// ── G4OCCTSolid static factory ────────────────────────────────────────────────
 
G4OCCTSolid* G4OCCTSolid::FromSTEP(const G4String& name, const std::string& path) {
  STEPControl_Reader reader;
  if (reader.ReadFile(path.c_str()) != IFSelect_RetDone) {
    throw std::runtime_error("G4OCCTSolid::FromSTEP: failed to read STEP file: " + path);
  }
  if (reader.TransferRoots() <= 0) {
    throw std::runtime_error("G4OCCTSolid::FromSTEP: no roots transferred from: " + path);
  }
  TopoDS_Shape shape = reader.OneShape();
  if (shape.IsNull()) {
    throw std::runtime_error("G4OCCTSolid::FromSTEP: null shape loaded from: " + path);
  }
  return new G4OCCTSolid(name, shape);
}
 
// ── G4OCCTSolid private helpers ───────────────────────────────────────────────
 
void G4OCCTSolid::ComputeBounds() {
  // Pre-build PCurves for edges on planar faces so BRep_Tool::CurveOnPlane()
  // returns the stored result on every Inside() query instead of recomputing
  // via GeomProjLib::ProjectOnPlane each time (~3.3% of total instructions).
  for (TopExp_Explorer faceEx(fShape, TopAbs_FACE); faceEx.More(); faceEx.Next()) {
    const TopoDS_Face& face = TopoDS::Face(faceEx.Current());
    if (BRepAdaptor_Surface(face).GetType() != GeomAbs_Plane) {
      continue;
    }
    for (TopExp_Explorer edgeEx(face, TopAbs_EDGE); edgeEx.More(); edgeEx.Next()) {
      BRepLib::BuildPCurveForEdgeOnPlane(TopoDS::Edge(edgeEx.Current()), face);
    }
  }
 
  Bnd_Box boundingBox;
  BRepBndLib::AddOptimal(fShape, boundingBox, /*useTriangulation=*/Standard_False);
  if (boundingBox.IsVoid()) {
    throw std::invalid_argument("G4OCCTSolid: shape has no computable bounding box (no geometry)");
  }
 
  Standard_Real xMin = 0.0;
  Standard_Real yMin = 0.0;
  Standard_Real zMin = 0.0;
  Standard_Real xMax = 0.0;
  Standard_Real yMax = 0.0;
  Standard_Real zMax = 0.0;
  boundingBox.Get(xMin, yMin, zMin, xMax, yMax, zMax);
 
  fCachedBounds =
      AxisAlignedBounds{G4ThreeVector(xMin, yMin, zMin), G4ThreeVector(xMax, yMax, zMax)};
 
  // Build per-face bounding-box cache for the SurfaceNormal prefilter.
  fFaceBoundsCache.clear();
  fFaceAdaptorIndex.clear();
  G4double maxFaceDiag = 0.0;
  for (TopExp_Explorer ex(fShape, TopAbs_FACE); ex.More(); ex.Next()) {
    Bnd_Box faceBox;
    BRepBndLib::AddOptimal(ex.Current(), faceBox, /*useTriangulation=*/Standard_False);
    const TopoDS_Face& currentFace = TopoDS::Face(ex.Current());
    const std::size_t idx          = fFaceBoundsCache.size();
    BRepAdaptor_Surface adaptor(currentFace);
    std::optional<gp_Pln> maybePlane;
    std::vector<gp_Pnt2d> uvPolygon;
    std::optional<G4ThreeVector> outwardNormal;
    if (adaptor.GetType() == GeomAbs_Plane) {
      maybePlane             = adaptor.Plane();
      const gp_Ax3& pos      = maybePlane->Position();
      const TopoDS_Wire wire = BRepTools::OuterWire(currentFace);
      if (!wire.IsNull()) {
        // Collect vertices of the outer wire in order via BRepTools_WireExplorer.
        // Only accept faces where every edge is a straight line segment: for faces
        // with curved edges (arcs, splines) the vertex-only polygon is an
        // under-approximation and would produce false misses.
        bool allLinear = true;
        std::vector<gp_Pnt2d> poly;
        for (BRepTools_WireExplorer we(wire, currentFace); we.More(); we.Next()) {
          const BRepAdaptor_Curve ec(we.Current());
          if (ec.GetType() != GeomAbs_Line) {
            allLinear = false;
            break;
          }
          const gp_Pnt pt = BRep_Tool::Pnt(we.CurrentVertex());
          Standard_Real u = 0.0;
          Standard_Real v = 0.0;
          ElSLib::PlaneParameters(pos, pt, u, v);
          poly.emplace_back(u, v);
        }
        if (allLinear && poly.size() >= 3) {
          // Verify the face has no inner wires (holes).  The outer-wire-only polygon
          // cannot represent cutouts: a ray hitting inside the outer boundary but
          // inside a hole would be incorrectly counted as a face crossing.
          int wireCount = 0;
          for (TopExp_Explorer wc(currentFace, TopAbs_WIRE); wc.More(); wc.Next()) {
            ++wireCount;
            if (wireCount > 1) {
              break;
            }
          }
          if (wireCount == 1) {
            uvPolygon = std::move(poly);
            // Precompute the constant outward face normal.  For planar faces the
            // normal is uniform; gp_Pln::Axis() points along the plane normal, but
            // the outward direction depends on the face orientation in the solid.
            gp_Dir faceNormal = maybePlane->Axis().Direction();
            if (currentFace.Orientation() == TopAbs_REVERSED) {
              faceNormal.Reverse();
            }
            outwardNormal = G4ThreeVector(faceNormal.X(), faceNormal.Y(), faceNormal.Z());
          }
        }
      }
    }
    fFaceBoundsCache.push_back({currentFace, faceBox, std::move(adaptor), std::move(maybePlane),
                                std::move(uvPolygon), std::move(outwardNormal)});
    fFaceAdaptorIndex[currentFace.TShape().get()].push_back(idx);
    // Track the largest face bounding-box diagonal to bound the tessellation error.
    if (!faceBox.IsVoid()) {
      Standard_Real fx0 = 0.0;
      Standard_Real fy0 = 0.0;
      Standard_Real fz0 = 0.0;
      Standard_Real fx1 = 0.0;
      Standard_Real fy1 = 0.0;
      Standard_Real fz1 = 0.0;
      faceBox.Get(fx0, fy0, fz0, fx1, fy1, fz1);
      const G4double diag = G4ThreeVector(fx1 - fx0, fy1 - fy0, fz1 - fz0).mag();
      maxFaceDiag         = std::max(maxFaceDiag, diag);
    }
  }
 
  // fBVHDeflection bounds the Hausdorff distance between the analytical surface
  // and the tessellation built with relative deflection kRelativeDeflection.
  fBVHDeflection = kRelativeDeflection * maxFaceDiag;
 
  // Determine if all faces are planar (enables the fast plane-distance path in DistanceToOut).
  fAllFacesPlanar = std::all_of(fFaceBoundsCache.begin(), fFaceBoundsCache.end(),
                                [](const FaceBounds& fb) { return fb.plane.has_value(); });
 
  // Ensure a triangulation is present (idempotent if mesh already exists).
  // Limit lifetime to this scope so mesh resources are released before building
  // the BVH, preserving the original temporary-object behavior.
  {
    [[maybe_unused]] const BRepMesh_IncrementalMesh mesher(fShape, kRelativeDeflection,
                                                           /*isRelative=*/Standard_True);
  }
 
  // Build the BVH-accelerated triangle set over all tessellated faces.
  BRepExtrema_ShapeList faces;
  for (TopExp_Explorer ex(fShape, TopAbs_FACE); ex.More(); ex.Next()) {
    faces.Append(ex.Current());
  }
  if (faces.IsEmpty()) {
    fTriangleSet.Nullify();
    fFaceDeflections.clear();
  } else {
    fTriangleSet = new BRepExtrema_TriangleSet(faces);
 
    // Build per-face deflection table indexed in the same order as fFaceBoundsCache
    // (and as the faces list above — both use the same TopExp_Explorer traversal).
    // At query time, BRepExtrema_TriangleSet::GetFaceID() maps the nearest triangle's
    // post-BVH-reorder index back to its face index, allowing a per-face lookup here.
    fFaceDeflections.clear();
    fFaceDeflections.reserve(fFaceBoundsCache.size());
    for (const FaceBounds& fb : fFaceBoundsCache) {
      // Start from the global BVH deflection so that per-face values never
      // reduce the safety margin below fBVHDeflection, even for faces with
      // a void bounding box or very small extent.
      G4double deflection = fBVHDeflection;
      if (!fb.box.IsVoid()) {
        Standard_Real fx0 = 0.0, fy0 = 0.0, fz0 = 0.0;
        Standard_Real fx1 = 0.0, fy1 = 0.0, fz1 = 0.0;
        fb.box.Get(fx0, fy0, fz0, fx1, fy1, fz1);
        const G4double faceDiag = G4ThreeVector(fx1 - fx0, fy1 - fy0, fz1 - fz0).mag();
        deflection              = kRelativeDeflection * faceDiag;
      }
      fFaceDeflections.push_back(deflection);
    }
  }
 
  ComputeInitialSpheres();
}
 
void G4OCCTSolid::ComputeInitialSpheres() {
  fInitialSpheres.clear();
 
  const G4double tol          = IntersectionTolerance();
  const G4ThreeVector& bmin   = fCachedBounds.min;
  const G4ThreeVector& bmax   = fCachedBounds.max;
  const G4ThreeVector centre  = 0.5 * (bmin + bmax);
  const G4ThreeVector halfExt = 0.5 * (bmax - bmin);
 
  // Candidate seed points: AABB centre, 6 axis-offset interior points (each at half
  // the distance from the AABB centre to the nearest face along that axis), and 8 octant
  // centres (15 total).
  std::vector<G4ThreeVector> candidates;
  candidates.reserve(15);
  candidates.push_back(centre);
  for (const G4double s : {-0.5, 0.5}) {
    candidates.push_back(centre + G4ThreeVector(s * halfExt.x(), 0.0, 0.0));
    candidates.push_back(centre + G4ThreeVector(0.0, s * halfExt.y(), 0.0));
    candidates.push_back(centre + G4ThreeVector(0.0, 0.0, s * halfExt.z()));
  }
  for (const int sx : {-1, 1}) {
    for (const int sy : {-1, 1}) {
      for (const int sz : {-1, 1}) {
        candidates.push_back(centre + G4ThreeVector(0.75 * sx * halfExt.x(),
                                                    0.75 * sy * halfExt.y(),
                                                    0.75 * sz * halfExt.z()));
      }
    }
  }
 
  // Use a local classifier: construction-time only, no thread-local needed.
  BRepClass3d_SolidClassifier localClassifier;
  localClassifier.Load(fShape);
 
  for (const G4ThreeVector& cand : candidates) {
    localClassifier.Perform(ToPoint(cand), tol);
    if (localClassifier.State() != TopAbs_IN) {
      continue;
    }
    G4double d = BVHLowerBoundDistance(cand);
    if (d >= kInfinity || d <= tol) {
      // BVH unavailable or too close to surface; try exact distance.
      const auto match = TryFindClosestFace(fFaceBoundsCache, cand);
      if (!match.has_value() || match->distance <= tol) {
        continue;
      }
      d = match->distance;
    }
    fInitialSpheres.push_back({cand, d});
  }
  // Sort descending by radius so the most useful spheres are checked first.
  std::sort(fInitialSpheres.begin(), fInitialSpheres.end(),
            [](const InscribedSphere& a, const InscribedSphere& b) { return a.radius > b.radius; });
}
 
std::optional<G4OCCTSolid::ClosestFaceMatch>
G4OCCTSolid::TryFindClosestFace(const std::vector<FaceBounds>& faceBoundsCache,
                                const G4ThreeVector& point, G4double maxDistance) {
  if (faceBoundsCache.empty()) {
    return std::nullopt;
  }
 
  const gp_Pnt queryPoint         = ToPoint(point);
  const TopoDS_Vertex queryVertex = MakeVertex(point);
 
  // Build the point box once — it is constant for the entire loop.
  Bnd_Box queryBox;
  queryBox.Add(queryPoint);
 
  std::optional<ClosestFaceMatch> bestMatch;
  for (std::size_t i = 0; i < faceBoundsCache.size(); ++i) {
    const FaceBounds& fb = faceBoundsCache[i];
    // Lower bound: distance from query point to the face's axis-aligned bounding box.
    // Use maxDistance as the initial pruning threshold (before a bestMatch is found),
    // tightening to bestMatch->distance once a candidate has been accepted.
    const G4double threshold = bestMatch.has_value() ? bestMatch->distance : maxDistance;
    if (threshold < kInfinity && fb.box.Distance(queryBox) > threshold) {
      continue;
    }
 
    // Use BRepExtrema_DistShapeShape for a robust point-to-face distance.
    // Extrema_ExtPS only finds interior critical points of the distance function
    // on the (unbounded) surface; for bilinear (degree-1) B-spline faces the
    // global minimum is often on the face boundary (an edge or vertex), which
    // Extrema_ExtPS misses.  BRepExtrema_DistShapeShape considers the bounded
    // face including all its edges and vertices, guaranteeing the true minimum.
    BRepExtrema_DistShapeShape distance(queryVertex, fb.face);
    if (!distance.IsDone() || distance.NbSolution() == 0) {
      continue;
    }
    const G4double candidateDistance = distance.Value();
 
    if (bestMatch.has_value() && candidateDistance >= bestMatch->distance) {
      continue;
    }
    ClosestFaceMatch match{.face = fb.face, .distance = candidateDistance, .faceIndex = i};
    // Extract UV from BRepExtrema when solution is on the face interior.
    // For edge/vertex solutions ParOnFaceS2 has a different meaning so we
    // skip caching in those cases and let SurfaceNormal fall back to
    // GeomAPI_ProjectPointOnSurf.
    if (distance.NbSolution() > 0 && distance.SupportTypeShape2(1) == BRepExtrema_IsInFace) {
      Standard_Real u = 0.0;
      Standard_Real v = 0.0;
      distance.ParOnFaceS2(1, u, v);
      match.uv = std::make_pair(u, v);
    }
    bestMatch = std::move(match);
  }
 
  return bestMatch;
}
 
BRepClass3d_SolidClassifier& G4OCCTSolid::GetOrCreateClassifier() const {
  ClassifierCache& cache         = fClassifierCache.Get();
  const std::uint64_t currentGen = fShapeGeneration.load(std::memory_order_acquire);
  if (cache.generation != currentGen) {
    cache.classifier.emplace();
    cache.classifier->Load(fShape); // O(N_faces) — paid once per thread per shape
    cache.generation = currentGen;
  }
  return *cache.classifier;
}
 
G4OCCTSolid::IntersectorCache& G4OCCTSolid::GetOrCreateIntersector() const {
  IntersectorCache& cache        = fIntersectorCache.Get();
  const std::uint64_t currentGen = fShapeGeneration.load(std::memory_order_acquire);
  if (cache.generation != currentGen) {
    const G4double tol = IntersectionTolerance();
    cache.faceIntersectors.clear();
    cache.faceIntersectors.reserve(fFaceBoundsCache.size());
    cache.expandedBoxes.clear();
    cache.expandedBoxes.reserve(fFaceBoundsCache.size());
    for (const auto& fb : fFaceBoundsCache) {
      cache.faceIntersectors.push_back(
          std::make_unique<IntCurvesFace_Intersector>(fb.face, tol)); // O(1) per face
      Bnd_Box expanded = fb.box;
      expanded.Enlarge(tol); // prevent false-positive IsOut for zero-thickness planar face boxes
      cache.expandedBoxes.push_back(std::move(expanded));
    }
    cache.generation = currentGen;
  }
  return cache;
}
 
G4OCCTSolid::SphereCacheData& G4OCCTSolid::GetOrInitSphereCache() const {
  SphereCacheData& cache         = fSphereCache.Get();
  const std::uint64_t currentGen = fShapeGeneration.load(std::memory_order_acquire);
  if (cache.generation != currentGen) {
    // Re-seed from the construction-time initial spheres (already sorted descending).
    cache.spheres    = fInitialSpheres;
    cache.generation = currentGen;
  }
  return cache;
}
 
void G4OCCTSolid::TryInsertSphere(const G4ThreeVector& centre, G4double d) const {
  if (d <= 0.0) {
    return;
  }
 
  // Enforce a minimum meaningful radius, consistent with ComputeInitialSpheres().
  const G4double minRadius = IntersectionTolerance();
  if (d <= minRadius) {
    return;
  }
  SphereCacheData& cache = GetOrInitSphereCache();
 
  // Quick capacity check: if at capacity and the new radius is no better than
  // the smallest stored radius, there is nothing to gain.
  if (cache.spheres.size() >= kMaxInscribedSpheres && d <= cache.spheres.back().radius) {
    return;
  }
 
  // Dominance check: skip if the new sphere is fully contained inside an existing one.
  // Condition: |centre − cᵢ| + d ≤ rᵢ  ↔  |centre − cᵢ|² ≤ (rᵢ − d)² (when rᵢ ≥ d).
  for (const InscribedSphere& s : cache.spheres) {
    if (s.radius >= d) {
      const G4double gap = s.radius - d;
      if ((centre - s.centre).mag2() <= gap * gap) {
        return;
      }
    }
  }
 
  // Insert in sorted position (descending by radius).
  const InscribedSphere newSphere{centre, d};
  const auto it = std::lower_bound(
      cache.spheres.begin(), cache.spheres.end(), newSphere,
      [](const InscribedSphere& a, const InscribedSphere& b) { return a.radius > b.radius; });
  cache.spheres.insert(it, newSphere);
 
  // Evict the smallest sphere if the cache has grown beyond capacity.
  if (cache.spheres.size() > kMaxInscribedSpheres) {
    cache.spheres.pop_back();
  }
}
 
// ── G4VSolid pure-virtual implementations ────────────────────────────────────
 
EInside G4OCCTSolid::Inside(const G4ThreeVector& p) const {
  const G4double tolerance = IntersectionTolerance();
  if (p.x() < fCachedBounds.min.x() - tolerance || p.x() > fCachedBounds.max.x() + tolerance ||
      p.y() < fCachedBounds.min.y() - tolerance || p.y() > fCachedBounds.max.y() + tolerance ||
      p.z() < fCachedBounds.min.z() - tolerance || p.z() > fCachedBounds.max.z() + tolerance) {
    return kOutside;
  }
 
  // Fast inscribed-sphere check: if p lies strictly inside any cached sphere
  // (with a tolerance margin), every such sphere is provably interior to the
  // solid, so we can return kInside immediately without an OCCT classifier call.
  // The check uses (radius - tolerance) to avoid misclassifying boundary-adjacent
  // points as kInside — matching the open-ball guarantee from the safety distance.
  const SphereCacheData& sphereCache = GetOrInitSphereCache();
  for (const InscribedSphere& s : sphereCache.spheres) {
    const G4double interiorRadius = s.radius - tolerance;
    if (interiorRadius > 0.0 && (p - s.centre).mag2() < interiorRadius * interiorRadius) {
      return kInside;
    }
  }
 
  // Tier-2a: BVH ray-parity test over the pre-built fTriangleSet.
  // Cast a +Z ray and count crossings via Möller–Trumbore in a single
  // O(log N_triangles) BVH traversal, replacing the per-face
  // IntCurvesFace_Intersector calls for curved faces.
  if (!fTriangleSet.IsNull() && fTriangleSet->Size() > 0) {
    // Guard: if the point is within the mesh error band (distance-to-surface
    // not provably greater than tolerance + deflection), the tessellation may
    // disagree with the exact solid near the boundary.  Fall back to the exact
    // classifier so the classification is always consistent with the analytic shape.
    if (fBVHDeflection > 0.0) {
      const G4double bvhLB = BVHLowerBoundDistance(p);
      if (bvhLB < tolerance) {
        BRepClass3d_SolidClassifier& classifier = GetOrCreateClassifier();
        classifier.Perform(ToPoint(p), tolerance);
        return ToG4Inside(classifier.State());
      }
    }
 
    // Multi-ray majority vote: cast up to three orthogonal rays (+Z, +X, +Y)
    // through the BVH triangle set and tally inside/outside votes.
    //
    // Fast path: if the primary (+Z) ray is non-degenerate and has a non-zero
    // crossing count, its parity is reliable and we return immediately.
    //
    // Slow path (primary degenerate or zero crossings): cast +X and +Y as
    // tie-breakers.  Only non-degenerate rays contribute a vote.  A clear
    // majority (more inside votes than outside, or vice versa) determines the
    // result.  If no majority can be established (all three rays degenerate, or
    // a genuine 1–1 tie), we fall back to the exact OCCT classifier.
    //
    // This eliminates BRepClass3d_SolidClassifier::Perform() calls for all but
    // the near-surface and all-degenerate cases, collapsing the CSLib_Class2d
    // and NCollection heap-allocation overhead for complex solids.
    const BVH_Vec3d bvhOrigin(p.x(), p.y(), p.z());
    const Standard_Real bvhTol = static_cast<Standard_Real>(tolerance);
    TriangleRayCast caster;
    caster.SetBVHSet(fTriangleSet.get());
 
    // Primary ray: +Z
    caster.SetRay(bvhOrigin, BVH_Vec3d(0.0, 0.0, 1.0), bvhTol);
    caster.Select();
 
    if (caster.OnSurface()) {
      return kSurface;
    }
 
    // Fast path: primary ray is unambiguous.
    if (!caster.Degenerate() && caster.Crossings() > 0) {
      return (caster.Crossings() % 2 == 1) ? kInside : kOutside;
    }
 
    // Primary is problematic (degenerate or zero crossings).  Tally its vote
    // (excluded if degenerate), then cast two more orthogonal rays.
    int insideVotes  = 0;
    int outsideVotes = 0;
    if (!caster.Degenerate()) {
      if (caster.Crossings() % 2 == 1) {
        ++insideVotes;
      } else {
        ++outsideVotes;
      }
    }
 
    const BVH_Vec3d kExtraRays[2] = {
        BVH_Vec3d(1.0, 0.0, 0.0),
        BVH_Vec3d(0.0, 1.0, 0.0),
    };
    for (const BVH_Vec3d& dir : kExtraRays) {
      caster.SetRay(bvhOrigin, dir, bvhTol);
      caster.Select();
      if (caster.OnSurface()) {
        return kSurface;
      }
      if (!caster.Degenerate()) {
        if (caster.Crossings() % 2 == 1) {
          ++insideVotes;
        } else {
          ++outsideVotes;
        }
      }
    }
 
    if (insideVotes > outsideVotes) {
      return kInside;
    }
    if (outsideVotes > insideVotes) {
      return kOutside;
    }
 
    // No majority (all degenerate, or genuine 1–1 tie): fall back to the exact
    // OCCT classifier.
    BRepClass3d_SolidClassifier& classifier = GetOrCreateClassifier();
    classifier.Perform(ToPoint(p), tolerance);
    return ToG4Inside(classifier.State());
  }
 
  // Tier-2b: fallback when fTriangleSet is unavailable — original per-face
  // ray-parity test using per-thread IntCurvesFace_Intersector cache.
  // Cast a ray from p in the canonical +Z direction and count how many faces
  // the ray crosses strictly through their interior (TopAbs_IN).  Odd = inside.
  // TopAbs_ON hits (shared edges/vertices) are excluded from the parity count;
  // any such hit signals a degenerate ray and triggers a classifier fallback so
  // that altered parity from skipping the crossing does not misclassify the point.
  IntersectorCache& cache = GetOrCreateIntersector();
  const gp_Lin ray(ToPoint(p), gp_Dir(0.0, 0.0, 1.0));
  int crossings      = 0;
  bool onSurface     = false;
  bool degenerateRay = false;
 
  for (std::size_t i = 0; i < fFaceBoundsCache.size(); ++i) {
    if (cache.expandedBoxes[i].IsOut(ray)) {
      continue;
    }
    const FaceBounds& fb = fFaceBoundsCache[i];
    if (!fb.uvPolygon.empty()) {
      // Fast path: direct ray–plane intersection without OCCT topology overhead.
      // Retrieve the UV hit coordinates so we can detect edge/vertex hits (which
      // would be TopAbs_ON in the OCCT intersector) and fall back to the
      // classifier just like the degenerate-ray path does for non-planar faces.
      Standard_Real u_hit = 0.0;
      Standard_Real v_hit = 0.0;
      const auto t        = RayPlaneFaceHit(ray, *fb.plane, fb.uvPolygon, -tolerance,
                                            Precision::Infinite(), tolerance, &u_hit, &v_hit);
      if (t) {
        const G4double w = static_cast<G4double>(*t);
        if (std::abs(w) <= tolerance) {
          onSurface = true;
        } else if (w > tolerance) {
          // Check whether the hit UV point is on the polygon boundary (within
          // tolerance): that corresponds to a TopAbs_ON state in the OCCT
          // intersector and requires the same degenerate-ray fallback.
          if (PointOnPolygonBoundary2d(u_hit, v_hit, fb.uvPolygon, tolerance)) {
            degenerateRay = true;
          } else {
            ++crossings;
          }
        }
      }
    } else {
      IntCurvesFace_Intersector& fi = *cache.faceIntersectors[i];
      fi.Perform(ray, -tolerance, Precision::Infinite());
      if (!fi.IsDone()) {
        continue;
      }
      for (Standard_Integer j = 1; j <= fi.NbPnt(); ++j) {
        const G4double w         = fi.WParameter(j);
        const TopAbs_State state = fi.State(j);
        if (std::abs(w) <= tolerance && (state == TopAbs_IN || state == TopAbs_ON)) {
          onSurface = true;
        } else if (w > tolerance && state == TopAbs_IN) {
          ++crossings;
        } else if (w > tolerance && state == TopAbs_ON) {
          degenerateRay = true;
        }
      }
    }
  }
 
  if (onSurface) {
    return kSurface;
  }
  // Safety fallback: use the classifier when the parity count is unreliable —
  // either because no TopAbs_IN crossings were found (ray may pass entirely
  // through edges/vertices) or because at least one TopAbs_ON edge/vertex hit
  // was skipped (altering the effective crossing count).
  if (crossings == 0 || degenerateRay) {
    BRepClass3d_SolidClassifier& classifier = GetOrCreateClassifier();
    classifier.Perform(ToPoint(p), tolerance);
    return ToG4Inside(classifier.State());
  }
  return (crossings % 2 == 1) ? kInside : kOutside;
}
 
G4ThreeVector G4OCCTSolid::SurfaceNormal(const G4ThreeVector& p) const {
  // Phase 1: all-planar fast path — O(N_faces) dot products, zero OCCT solver calls.
  // For planar solids every face's outward normal is constant and precomputed in
  // fFaceBoundsCache.  The closest face is identified by the minimum plane distance.
  if (fAllFacesPlanar) {
    const gp_Pnt pt          = ToPoint(p);
    const FaceBounds* bestFB = nullptr;
    G4double bestDist        = kInfinity;
    for (const FaceBounds& fb : fFaceBoundsCache) {
      if (!fb.plane.has_value() || !fb.outwardNormal.has_value()) {
        continue;
      }
      const G4double d = fb.plane->Distance(pt);
      if (d < bestDist) {
        bestDist = d;
        bestFB   = &fb;
      }
    }
    if (bestFB) {
      return *bestFB->outwardNormal;
    }
  }
 
  // Phase 2: BVH-seeded face identification for curved (or mixed) solids.
  //
  // Use face-local extrema + projection instead of a single solid-wide
  // BRepExtrema_DistShapeShape(vertex, solid) query. On imported periodic
  // surfaces (notably the torus seam hit at (15,0,0) in the geometry-fixture
  // tests), the solid-wide path can descend into OCCT's 2D seam classifier and
  // either wedge in boundary classification or report an edge-supported
  // solution whose direct normal evaluation falls back to +Z. Face-local
  // selection still identifies the nearest supporting face, while the explicit
  // projection step recovers a usable (u,v) pair that we can nudge off exact
  // periodic seams before asking OCCT for derivatives. Revisit this once the
  // upstream periodic-classifier fix is available everywhere we build.
  //
  // BVHLowerBoundDistance gives a lower bound on the true distance to the surface.
  // Adding 2×fBVHDeflection (Hausdorff bound between tessellation and analytical
  // surface) yields a valid upper bound on the distance to the nearest surface point.
  // This seed is passed to TryFindClosestFace to prune faces that are provably
  // farther away, reducing the number of BRepExtrema calls for multi-face solids.
  // TryFindClosestFace then uses exact BRepExtrema on every candidate, guaranteeing
  // the correct nearest face is returned regardless of tessellation approximation
  // errors (which could fool a pure-BVH face-identification approach).
 
  // Shared helper: project @p onto @face using a pre-built surface adaptor,
  // obtain (u,v), and evaluate the outward normal.  Accepting the cached
  // BRepAdaptor_Surface avoids reconstructing it on the fly on this hot path.
  const auto projectAndGetNormalFallback = [&](const FaceBounds& fb) -> G4ThreeVector {
    TopLoc_Location loc;
    const Handle(Geom_Surface) surface = BRep_Tool::Surface(fb.face, loc);
    if (surface.IsNull()) {
      return FallbackNormal();
    }
    gp_Pnt pLocal = ToPoint(p);
    if (!loc.IsIdentity()) {
      pLocal.Transform(loc.Transformation().Inverted());
    }
    GeomAPI_ProjectPointOnSurf projection(pLocal, surface);
    if (projection.NbPoints() == 0) {
      return FallbackNormal();
    }
    Standard_Real u = 0.0;
    Standard_Real v = 0.0;
    projection.LowerDistanceParameters(u, v);
    return TryGetOutwardNormal(fb.adaptor, fb.face, u, v).value_or(FallbackNormal());
  };
 
  const G4double bvhLB = BVHLowerBoundDistance(p);
  const G4double seedDist =
      (fBVHDeflection > 0.0 && bvhLB < kInfinity) ? bvhLB + 2.0 * fBVHDeflection : kInfinity;
  const auto closestFaceMatch = TryFindClosestFace(fFaceBoundsCache, p, seedDist);
  if (!closestFaceMatch.has_value()) {
    return FallbackNormal();
  }
  const FaceBounds& fb = fFaceBoundsCache[closestFaceMatch->faceIndex];
 
  // Fast-path A: planar face with precomputed constant outward normal.
  // Applies even in mixed solids (e.g. G4CutTubs) where fAllFacesPlanar is
  // false but the closest face happens to be a flat endcap.
  if (fb.outwardNormal.has_value()) {
    return *fb.outwardNormal;
  }
 
  // Fast-path B: reuse UV already computed by BRepExtrema_DistShapeShape
  // when the solution is on the face interior, skipping GeomAPI_ProjectPointOnSurf.
  if (closestFaceMatch->uv.has_value()) {
    const auto [u, v] = *closestFaceMatch->uv;
    const auto result = TryGetOutwardNormal(fb.adaptor, fb.face, u, v);
    if (result.has_value()) {
      return *result;
    }
    // Fall through to full projection if normal evaluation failed at stored UV
    // (e.g. torus seam or degenerate point).
  }
 
  // Fallback: full GeomAPI_ProjectPointOnSurf reprojection for edge/vertex
  // solutions and cases where TryGetOutwardNormal returned nullopt.
  return projectAndGetNormalFallback(fb);
}
 
G4double G4OCCTSolid::DistanceToIn(const G4ThreeVector& p, const G4ThreeVector& v) const {
  const G4double tolerance = IntersectionTolerance();
  const gp_Lin ray(ToPoint(p), gp_Dir(v.x(), v.y(), v.z()));
 
  IntersectorCache& cache = GetOrCreateIntersector();
 
  G4double minDistance = kInfinity;
  for (std::size_t i = 0; i < fFaceBoundsCache.size(); ++i) {
    if (cache.expandedBoxes[i].IsOut(ray)) {
      continue;
    }
    const FaceBounds& fb = fFaceBoundsCache[i];
    if (!fb.uvPolygon.empty()) {
      // Fast path: bypass IntCurvesFace_Intersector for straight-edge planar faces.
      const auto t = RayPlaneFaceHit(ray, *fb.plane, fb.uvPolygon, tolerance, Precision::Infinite(),
                                     tolerance);
      if (t && *t < minDistance) {
        minDistance = static_cast<G4double>(*t);
      }
    } else {
      IntCurvesFace_Intersector& fi = *cache.faceIntersectors[i];
      fi.Perform(ray, tolerance, Precision::Infinite());
      if (!fi.IsDone()) {
        continue;
      }
      for (Standard_Integer j = 1; j <= fi.NbPnt(); ++j) {
        const G4double w = fi.WParameter(j);
        if (w > tolerance && w < minDistance) {
          minDistance = w;
        }
      }
    }
  }
 
  return minDistance;
}
 
G4double G4OCCTSolid::ExactDistanceToIn(const G4ThreeVector& p) const {
  BRepClass3d_SolidClassifier& classifier = GetOrCreateClassifier();
  classifier.Perform(ToPoint(p), IntersectionTolerance());
  if (classifier.State() == TopAbs_IN || classifier.State() == TopAbs_ON) {
    return 0.0;
  }
 
  const auto match = TryFindClosestFace(fFaceBoundsCache, p);
  if (!match.has_value()) {
    return kInfinity;
  }
  return (match->distance <= IntersectionTolerance()) ? 0.0 : match->distance;
}
 
G4double G4OCCTSolid::AABBLowerBound(const G4ThreeVector& p) const {
  const G4ThreeVector& mn = fCachedBounds.min;
  const G4ThreeVector& mx = fCachedBounds.max;
  const G4double dx       = std::max({0.0, mn.x() - p.x(), p.x() - mx.x()});
  const G4double dy       = std::max({0.0, mn.y() - p.y(), p.y() - mx.y()});
  const G4double dz       = std::max({0.0, mn.z() - p.z(), p.z() - mx.z()});
  return std::sqrt(dx * dx + dy * dy + dz * dz);
}
 
G4double G4OCCTSolid::BVHLowerBoundDistance(const G4ThreeVector& p) const {
  if (fTriangleSet.IsNull() || fTriangleSet->Size() == 0) {
    return kInfinity;
  }
  PointToMeshDistance solver;
  solver.SetObject(BVH_Vec3d(p.x(), p.y(), p.z()));
  solver.SetBVHSet(fTriangleSet.get());
  const Standard_Real meshDistSq = solver.ComputeDistance();
  if (!solver.IsDone()) {
    return kInfinity;
  }
  // The solver returns a squared distance; take the single sqrt here
  // before subtracting the deflection bound (which is in actual-distance space).
  const G4double meshDist = std::sqrt(static_cast<G4double>(meshDistSq));
 
  // Use per-face deflection for the face owning the nearest triangle.
  // BRepExtrema_TriangleSet::GetFaceID() maps the BVH-reordered triangle index
  // back to the face index in fFaceBoundsCache (the same ordering used to build
  // the shape list passed to fTriangleSet).  This is tighter than fBVHDeflection
  // when the nearest triangle belongs to a small face.
  G4double deflection            = fBVHDeflection;
  const Standard_Integer bestIdx = solver.BestIndex();
  if (bestIdx >= 0) {
    const Standard_Integer faceId = fTriangleSet->GetFaceID(bestIdx);
    if (faceId >= 0 && static_cast<std::size_t>(faceId) < fFaceDeflections.size()) {
      deflection = fFaceDeflections[static_cast<std::size_t>(faceId)];
    }
  }
 
  return std::max(0.0, meshDist - deflection);
}
 
G4double G4OCCTSolid::PlanarFaceLowerBoundDistance(const G4ThreeVector& p) const {
  const gp_Pnt pt  = ToPoint(p);
  G4double minDist = kInfinity;
  for (const FaceBounds& fb : fFaceBoundsCache) {
    if (!fb.plane.has_value()) {
      continue;
    }
    const G4double d = static_cast<G4double>(fb.plane->Distance(pt));
    if (d < minDist) {
      minDist = d;
    }
  }
  return minDist;
}
 
G4double G4OCCTSolid::DistanceToIn(const G4ThreeVector& p) const {
  // Tier-0: AABB lower bound (O(1)).  If the point is clearly outside the shape's
  // axis-aligned bounding box, the AABB distance is a guaranteed conservative lower
  // bound on the true surface distance and avoids any further OCCT computation.
  const G4double aabbDist = AABBLowerBound(p);
  if (aabbDist > IntersectionTolerance()) {
    return aabbDist;
  }
 
  // Tier-1: BVH triangle-mesh lower bound — O(log N_triangles).
  // For outside points this is a valid conservative lower bound (as required for
  // safety distances).  Avoids the expensive per-face BRepExtrema_DistShapeShape
  // calls that dominate ExactDistanceToIn for curved surfaces (e.g. ellipsoids).
  const G4double bvhDist = BVHLowerBoundDistance(p);
  if (bvhDist < kInfinity && bvhDist > IntersectionTolerance()) {
    return bvhDist;
  }
 
  // Fallback: exact distance (handles points near or inside the surface, including
  // interior/surface classification).
  return ExactDistanceToIn(p);
}
 
G4double G4OCCTSolid::DistanceToOut(const G4ThreeVector& p, const G4ThreeVector& v,
                                    const G4bool calcNorm, G4bool* validNorm,
                                    G4ThreeVector* n) const {
  if (validNorm != nullptr) {
    *validNorm = false;
  }
 
  const G4double tolerance = IntersectionTolerance();
  const gp_Lin ray(ToPoint(p), gp_Dir(v.x(), v.y(), v.z()));
 
  IntersectorCache& cache = GetOrCreateIntersector();
 
  G4double minDistance   = kInfinity;
  std::size_t minFaceIdx = std::numeric_limits<std::size_t>::max();
  G4double minU          = 0.0;
  G4double minV          = 0.0;
  bool minIsIn           = false;
  bool minIsFastPath     = false;
 
  for (std::size_t i = 0; i < fFaceBoundsCache.size(); ++i) {
    if (cache.expandedBoxes[i].IsOut(ray)) {
      continue;
    }
    const FaceBounds& fb = fFaceBoundsCache[i];
    if (!fb.uvPolygon.empty()) {
      // Fast path: direct ray–plane intersection for straight-edge planar faces.
      const auto t = RayPlaneFaceHit(ray, *fb.plane, fb.uvPolygon, tolerance, Precision::Infinite(),
                                     tolerance);
      if (t && *t < minDistance) {
        minDistance   = static_cast<G4double>(*t);
        minFaceIdx    = i;
        minIsIn       = true; // mirrors OCCT path: TopAbs_IN and TopAbs_ON both trigger normal
        minIsFastPath = true;
      }
    } else {
      IntCurvesFace_Intersector& fi = *cache.faceIntersectors[i];
      fi.Perform(ray, tolerance, Precision::Infinite());
      if (!fi.IsDone()) {
        continue;
      }
      for (Standard_Integer j = 1; j <= fi.NbPnt(); ++j) {
        const G4double w = fi.WParameter(j);
        if (w > tolerance && w < minDistance) {
          minDistance   = w;
          minFaceIdx    = i;
          minU          = fi.UParameter(j);
          minV          = fi.VParameter(j);
          minIsIn       = (fi.State(j) == TopAbs_IN || fi.State(j) == TopAbs_ON);
          minIsFastPath = false;
        }
      }
    }
  }
 
  if (minFaceIdx == std::numeric_limits<std::size_t>::max() || minDistance == kInfinity) {
    return 0.0;
  }
 
  if (calcNorm && validNorm != nullptr && n != nullptr && minIsIn) {
    const FaceBounds& fb = fFaceBoundsCache[minFaceIdx];
    if (minIsFastPath && fb.outwardNormal.has_value()) {
      // Fast path: use the precomputed constant outward normal for planar faces.
      *n         = *fb.outwardNormal;
      *validNorm = true;
    } else {
      const auto outNorm = TryGetOutwardNormal(fb.adaptor, fb.face, minU, minV);
      if (outNorm) {
        *n         = *outNorm;
        *validNorm = true;
      }
    }
  }
 
  return minDistance;
}
 
G4double G4OCCTSolid::ExactDistanceToOut(const G4ThreeVector& p) const {
  // Use the pre-built per-face AABB cache to prune candidates before calling
  // BRepExtrema on individual faces: each query performs O(N_faces) cheap AABB
  // checks, but only O(k) faces require expensive extrema evaluations.
  const auto match = TryFindClosestFace(fFaceBoundsCache, p);
  if (!match.has_value()) {
    return 0.0;
  }
  return (match->distance <= IntersectionTolerance()) ? 0.0 : match->distance;
}
 
G4double G4OCCTSolid::DistanceToOut(const G4ThreeVector& p) const {
  G4double d;
  if (fAllFacesPlanar) {
    // All faces are planar: the minimum perpendicular plane distance is exact
    // for convex solids and a valid conservative lower bound for all others.
    // This avoids the BVH triangle-mesh traversal entirely.
    d = PlanarFaceLowerBoundDistance(p);
    if (d == kInfinity) {
      d = ExactDistanceToOut(p);
    }
  } else {
    // Mixed geometry (some curved faces): the planar lower bound does not cover
    // curved faces and is not a valid bound on the true distance.  Fall back to
    // the BVH lower bound which covers all triangulated faces.
    const G4double bvhDist = BVHLowerBoundDistance(p);
    d                      = (bvhDist < kInfinity) ? bvhDist : ExactDistanceToOut(p);
  }
  // Feed the inscribed-sphere cache: every positive return value proves B(p,d)
  // is inside the solid and can accelerate future Inside(p) calls.
  TryInsertSphere(p, d);
  return d;
}
 
G4double G4OCCTSolid::GetCubicVolume() {
  std::unique_lock<std::mutex> lock(fVolumeAreaMutex);
  if (!fCachedVolume) {
    GProp_GProps props;
    BRepGProp::VolumeProperties(fShape, props);
    fCachedVolume = props.Mass();
  }
  return *fCachedVolume;
}
 
G4double G4OCCTSolid::GetSurfaceArea() {
  std::unique_lock<std::mutex> lock(fVolumeAreaMutex);
  if (!fCachedSurfaceArea) {
    GProp_GProps props;
    BRepGProp::SurfaceProperties(fShape, props);
    fCachedSurfaceArea = props.Mass();
  }
  return *fCachedSurfaceArea;
}
 
const G4OCCTSolid::SurfaceSamplingCache& G4OCCTSolid::GetOrBuildSurfaceCache() const {
  // Tessellate first, outside the lock: BRepMesh_IncrementalMesh is idempotent
  // and calling it from multiple threads simultaneously is safe (extra calls
  // after the first are no-ops).
  BRepMesh_IncrementalMesh mesher(fShape, kRelativeDeflection, /*isRelative=*/Standard_True);
  (void)mesher;
 
  std::unique_lock<std::mutex> lock(fSurfaceCacheMutex);
 
  const std::uint64_t currentGen = fShapeGeneration.load(std::memory_order_acquire);
  if (fSurfaceCache.has_value() && fSurfaceCacheGeneration == currentGen) {
    return *fSurfaceCache;
  }
 
  // Build the cache while holding the lock.  Collecting triangle vertices and
  // computing areas is fast (just reading the already-computed triangulation)
  // so blocking other threads briefly is acceptable.
  SurfaceSamplingCache cache;
 
  for (TopExp_Explorer ex(fShape, TopAbs_FACE); ex.More(); ex.Next()) {
    const TopoDS_Face& face = TopoDS::Face(ex.Current());
    TopLoc_Location loc;
    const Handle(Poly_Triangulation) & triangulation = BRep_Tool::Triangulation(face, loc);
    if (triangulation.IsNull()) {
      continue;
    }
 
    // Register this face once in the deduplicated faces array.
    const auto faceIndex = static_cast<std::uint32_t>(cache.faces.size());
    cache.faces.push_back(face);
 
    const gp_Trsf& transform  = loc.Transformation();
    const bool reverseWinding = face.Orientation() == TopAbs_REVERSED;
 
    for (Standard_Integer i = 1; i <= triangulation->NbTriangles(); ++i) {
      Standard_Integer idx1 = 0;
      Standard_Integer idx2 = 0;
      Standard_Integer idx3 = 0;
      triangulation->Triangle(i).Get(idx1, idx2, idx3);
      if (reverseWinding) {
        std::swap(idx2, idx3);
      }
 
      const gp_Pnt q1 = triangulation->Node(idx1).Transformed(transform);
      const gp_Pnt q2 = triangulation->Node(idx2).Transformed(transform);
      const gp_Pnt q3 = triangulation->Node(idx3).Transformed(transform);
 
      const G4ThreeVector v1(q1.X(), q1.Y(), q1.Z());
      const G4ThreeVector v2(q2.X(), q2.Y(), q2.Z());
      const G4ThreeVector v3(q3.X(), q3.Y(), q3.Z());
 
      const G4double area = 0.5 * (v2 - v1).cross(v3 - v1).mag();
      if (area > 0.0) {
        cache.totalArea += area;
        cache.cumulativeAreas.push_back(cache.totalArea);
        cache.triangles.push_back({v1, v2, v3, faceIndex});
      }
    }
  }
 
  fSurfaceCache           = std::move(cache);
  fSurfaceCacheGeneration = currentGen;
  return *fSurfaceCache;
}
 
G4ThreeVector G4OCCTSolid::GetPointOnSurface() const {
  const SurfaceSamplingCache& cache = GetOrBuildSurfaceCache();
 
  if (cache.triangles.empty() || cache.totalArea == 0.0) {
    G4ExceptionDescription msg;
    msg << "Tessellation of solid \"" << GetName()
        << "\" produced no valid triangles; cannot sample a point on the surface.";
    G4Exception("G4OCCTSolid::GetPointOnSurface", "GeomMgt1001", FatalException, msg);
    return {0.0, 0.0, 0.0}; // unreachable; silences compiler warning
  }
 
  // Select a triangle with probability proportional to its area using a
  // binary search on the cumulative-area array.
  const G4double target = G4UniformRand() * cache.totalArea;
  const auto it         = std::ranges::lower_bound(cache.cumulativeAreas, target);
  const std::size_t idx = std::min(static_cast<std::size_t>(it - cache.cumulativeAreas.begin()),
                                   cache.triangles.size() - 1);
  const SurfaceTriangle& chosen = cache.triangles[idx];
 
  // Sample uniformly within the chosen triangle using the standard
  // barycentric-coordinate technique: fold the unit square into a triangle
  // by reflecting points with r1+r2 > 1.
  G4double r1 = G4UniformRand();
  G4double r2 = G4UniformRand();
  if (r1 + r2 > 1.0) {
    r1 = 1.0 - r1;
    r2 = 1.0 - r2;
  }
 
  const G4ThreeVector tessPoint =
      chosen.p1 + r1 * (chosen.p2 - chosen.p1) + r2 * (chosen.p3 - chosen.p1);
 
  // For curved faces the tessellation triangle is a planar chord that lies
  // inside the solid.  Project the sampled point back to the nearest point on
  // the analytical face surface so that the returned point truly lies on the
  // boundary and passes the G4PVPlacement::CheckOverlaps() surface test.
  const TopoDS_Face& face = cache.faces[chosen.faceIndex];
  TopLoc_Location loc;
  const Handle(Geom_Surface) geomSurface = BRep_Tool::Surface(face, loc);
  if (!geomSurface.IsNull()) {
    gp_Pnt tessPointLocal(tessPoint.x(), tessPoint.y(), tessPoint.z());
    if (!loc.IsIdentity()) {
      tessPointLocal.Transform(loc.Transformation().Inverted());
    }
    GeomAPI_ProjectPointOnSurf projection(tessPointLocal, geomSurface);
    if (projection.NbPoints() > 0) {
      gp_Pnt projectedPoint = projection.NearestPoint();
      if (!loc.IsIdentity()) {
        projectedPoint.Transform(loc.Transformation());
      }
      return {projectedPoint.X(), projectedPoint.Y(), projectedPoint.Z()};
    }
  }
 
  return tessPoint;
}
 
G4GeometryType G4OCCTSolid::GetEntityType() const { return "G4OCCTSolid"; }
 
G4VisExtent G4OCCTSolid::GetExtent() const {
  return {fCachedBounds.min.x(), fCachedBounds.max.x(), fCachedBounds.min.y(),
          fCachedBounds.max.y(), fCachedBounds.min.z(), fCachedBounds.max.z()};
}
 
void G4OCCTSolid::BoundingLimits(G4ThreeVector& pMin, G4ThreeVector& pMax) const {
  pMin = fCachedBounds.min;
  pMax = fCachedBounds.max;
}
 
G4bool G4OCCTSolid::CalculateExtent(const EAxis pAxis, const G4VoxelLimits& pVoxelLimit,
                                    const G4AffineTransform& pTransform, G4double& pMin,
                                    G4double& pMax) const {
  const G4BoundingEnvelope envelope(fCachedBounds.min, fCachedBounds.max);
  return envelope.CalculateExtent(pAxis, pVoxelLimit, G4Transform3D(pTransform), pMin, pMax);
}
 
void G4OCCTSolid::DescribeYourselfTo(G4VGraphicsScene& scene) const { scene.AddSolid(*this); }
 
G4Polyhedron* G4OCCTSolid::CreatePolyhedron() const {
  const auto currentGeneration = fShapeGeneration.load(std::memory_order_acquire);
 
  {
    std::unique_lock<std::mutex> lock(fPolyhedronMutex);
 
    // Wait until no other thread is mid-build for a *different* generation, or
    // until the cache is already populated for our generation (fast path).
    fPolyhedronCV.wait(lock, [this, currentGeneration] {
      return !fPolyhedronBuilding || fPolyhedronGeneration == currentGeneration;
    });
 
    // Cache hit: return an independent copy to the caller.
    if (fCachedPolyhedron && fPolyhedronGeneration == currentGeneration) {
      return new G4Polyhedron(*fCachedPolyhedron);
    }
 
    // Claim the build slot so other concurrent callers wait for this thread.
    fPolyhedronBuilding = true;
  }
 
  // ── Tessellation outside the lock ─────────────────────────────────────────
  // Use a relative deflection (1 % of each face's bounding-box size) so that
  // the mesh density scales with the shape rather than being a fixed world-
  // space length that is inappropriate for both very small and very large
  // shapes.
  BRepMesh_IncrementalMesh mesher(fShape, kRelativeDeflection, /*isRelative=*/Standard_True);
  (void)mesher;
 
  G4TessellatedSolid tessellatedSolid(GetName() + "_polyhedron");
  G4int facetCount = 0;
 
  for (TopExp_Explorer explorer(fShape, TopAbs_FACE); explorer.More(); explorer.Next()) {
    const TopoDS_Face& face = TopoDS::Face(explorer.Current());
    TopLoc_Location location;
    const Handle(Poly_Triangulation) & triangulation = BRep_Tool::Triangulation(face, location);
    if (triangulation.IsNull()) {
      continue;
    }
 
    const gp_Trsf& transform  = location.Transformation();
    const bool reverseWinding = face.Orientation() == TopAbs_REVERSED;
 
    for (Standard_Integer triangleIndex = 1; triangleIndex <= triangulation->NbTriangles();
         ++triangleIndex) {
      Standard_Integer index1 = 0;
      Standard_Integer index2 = 0;
      Standard_Integer index3 = 0;
      triangulation->Triangle(triangleIndex).Get(index1, index2, index3);
 
      if (reverseWinding) {
        std::swap(index2, index3);
      }
 
      const gp_Pnt point1 = triangulation->Node(index1).Transformed(transform);
      const gp_Pnt point2 = triangulation->Node(index2).Transformed(transform);
      const gp_Pnt point3 = triangulation->Node(index3).Transformed(transform);
 
      auto* facet =
          new G4TriangularFacet(G4ThreeVector(point1.X(), point1.Y(), point1.Z()),
                                G4ThreeVector(point2.X(), point2.Y(), point2.Z()),
                                G4ThreeVector(point3.X(), point3.Y(), point3.Z()), ABSOLUTE);
      if (!facet->IsDefined() || !tessellatedSolid.AddFacet(facet)) {
        delete facet;
        continue;
      }
 
      ++facetCount;
    }
  }
 
  // Finalise the tessellated solid and build a polyhedron from it (still
  // outside the lock — both objects are local to this thread).
  std::unique_ptr<G4Polyhedron> freshPolyhedron;
  if (facetCount > 0) {
    tessellatedSolid.SetSolidClosed(true);
    G4Polyhedron* tmp = tessellatedSolid.GetPolyhedron();
    if (tmp != nullptr) {
      freshPolyhedron = std::make_unique<G4Polyhedron>(*tmp);
    }
  }
 
  // ── Write cache and wake waiters ──────────────────────────────────────────
  {
    std::unique_lock<std::mutex> lock(fPolyhedronMutex);
 
    // Only persist the result if the shape has not been replaced while
    // tessellation was running.  Re-reading the generation under the mutex
    // ensures the check and the write are atomic with respect to SetOCCTShape().
    bool cacheWritten = false;
    if (freshPolyhedron && fShapeGeneration.load(std::memory_order_acquire) == currentGeneration) {
      fCachedPolyhedron     = std::make_unique<G4Polyhedron>(*freshPolyhedron);
      fPolyhedronGeneration = currentGeneration;
      cacheWritten          = true;
    }
 
    // Clear the build slot *after* the cache write so that threads woken by
    // notify_all() see the complete, consistent cache state.
    fPolyhedronBuilding = false;
    fPolyhedronCV.notify_all();
 
    // Return a copy of the freshly-cached polyhedron when possible; fall back
    // to the locally-built one if the shape was replaced mid-tessellation.
    if (cacheWritten) {
      return new G4Polyhedron(*fCachedPolyhedron);
    }
  }
 
  return freshPolyhedron ? new G4Polyhedron(*freshPolyhedron) : nullptr;
}
 
std::ostream& G4OCCTSolid::StreamInfo(std::ostream& os) const {
  os << "-----------------------------------------------------------\n"
     << "    *** Dump for solid - " << GetName() << " ***\n"
     << "    ===================================================\n"
     << " Solid type: G4OCCTSolid\n"
     << " OCCT shape type: " << fShape.ShapeType() << "\n"
     << "-----------------------------------------------------------\n";
  return os;
}