add assimp submodule

1 files changed, 765 insertions, 0 deletions

diff --git a/src/mesh/assimp-master/code/AssetLib/IFC/IFCBoolean.cpp b/src/mesh/assimp-master/code/AssetLib/IFC/IFCBoolean.cpp
new file mode 100644
index 0000000..36912a7
--- /dev/null
+++ b/src/mesh/assimp-master/code/AssetLib/IFC/IFCBoolean.cpp
@@ -0,0 +1,765 @@
+/*
+Open Asset Import Library (assimp)
+----------------------------------------------------------------------
+
+Copyright (c) 2006-2022, assimp team
+All rights reserved.
+
+Redistribution and use of this software in source and binary forms,
+with or without modification, are permitted provided that the
+following conditions are met:
+
+* Redistributions of source code must retain the above
+  copyright notice, this list of conditions and the
+  following disclaimer.
+
+* Redistributions in binary form must reproduce the above
+  copyright notice, this list of conditions and the
+  following disclaimer in the documentation and/or other
+  materials provided with the distribution.
+
+* Neither the name of the assimp team, nor the names of its
+  contributors may be used to endorse or promote products
+  derived from this software without specific prior
+  written permission of the assimp team.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+----------------------------------------------------------------------
+*/
+
+/** @file  IFCBoolean.cpp
+ *  @brief Implements a subset of Ifc boolean operations
+ */
+
+#ifndef ASSIMP_BUILD_NO_IFC_IMPORTER
+
+#include "AssetLib/IFC/IFCUtil.h"
+#include "Common/PolyTools.h"
+#include "PostProcessing/ProcessHelper.h"
+
+
+#include <iterator>
+#include <tuple>
+
+namespace Assimp {
+namespace IFC {
+
+// ------------------------------------------------------------------------------------------------
+// Calculates intersection between line segment and plane. To catch corner cases, specify which side you prefer.
+// The function then generates a hit only if the end is beyond a certain margin in that direction, filtering out
+// "very close to plane" ghost hits as long as start and end stay directly on or within the given plane side.
+bool IntersectSegmentPlane(const IfcVector3 &p, const IfcVector3 &n, const IfcVector3 &e0,
+        const IfcVector3 &e1, bool assumeStartOnWhiteSide, IfcVector3 &out) {
+    const IfcVector3 pdelta = e0 - p, seg = e1 - e0;
+    const IfcFloat dotOne = n * seg, dotTwo = -(n * pdelta);
+
+    // if segment ends on plane, do not report a hit. We stay on that side until a following segment starting at this
+    // point leaves the plane through the other side
+    if (std::abs(dotOne + dotTwo) < ai_epsilon)
+        return false;
+
+    // if segment starts on the plane, report a hit only if the end lies on the *other* side
+    if (std::abs(dotTwo) < ai_epsilon) {
+        if ((assumeStartOnWhiteSide && dotOne + dotTwo < ai_epsilon) || (!assumeStartOnWhiteSide && dotOne + dotTwo > -ai_epsilon)) {
+            out = e0;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    // ignore if segment is parallel to plane and far away from it on either side
+    // Warning: if there's a few thousand of such segments which slowly accumulate beyond the epsilon, no hit would be registered
+    if (std::abs(dotOne) < ai_epsilon)
+        return false;
+
+    // t must be in [0..1] if the intersection point is within the given segment
+    const IfcFloat t = dotTwo / dotOne;
+    if (t > 1.0 || t < 0.0)
+        return false;
+
+    out = e0 + t * seg;
+    return true;
+}
+
+// ------------------------------------------------------------------------------------------------
+void FilterPolygon(std::vector<IfcVector3> &resultpoly) {
+    if (resultpoly.size() < 3) {
+        resultpoly.clear();
+        return;
+    }
+
+    IfcVector3 vmin, vmax;
+    ArrayBounds(resultpoly.data(), static_cast<unsigned int>(resultpoly.size()), vmin, vmax);
+
+    // filter our IfcFloat points - those may happen if a point lies
+    // directly on the intersection line or directly on the clipping plane
+    const IfcFloat epsilon = (vmax - vmin).SquareLength() / 1e6f;
+    FuzzyVectorCompare fz(epsilon);
+    std::vector<IfcVector3>::iterator e = std::unique(resultpoly.begin(), resultpoly.end(), fz);
+
+    if (e != resultpoly.end())
+        resultpoly.erase(e, resultpoly.end());
+
+    if (!resultpoly.empty() && fz(resultpoly.front(), resultpoly.back()))
+        resultpoly.pop_back();
+}
+
+// ------------------------------------------------------------------------------------------------
+void WritePolygon(std::vector<IfcVector3> &resultpoly, TempMesh &result) {
+    FilterPolygon(resultpoly);
+
+    if (resultpoly.size() > 2) {
+        result.mVerts.insert(result.mVerts.end(), resultpoly.begin(), resultpoly.end());
+        result.mVertcnt.push_back(static_cast<unsigned int>(resultpoly.size()));
+    }
+}
+
+// ------------------------------------------------------------------------------------------------
+void ProcessBooleanHalfSpaceDifference(const Schema_2x3::IfcHalfSpaceSolid *hs, TempMesh &result,
+        const TempMesh &first_operand,
+        ConversionData & /*conv*/) {
+    ai_assert(hs != nullptr);
+
+    const Schema_2x3::IfcPlane *const plane = hs->BaseSurface->ToPtr<Schema_2x3::IfcPlane>();
+    if (!plane) {
+        IFCImporter::LogError("expected IfcPlane as base surface for the IfcHalfSpaceSolid");
+        return;
+    }
+
+    // extract plane base position vector and normal vector
+    IfcVector3 p, n(0.f, 0.f, 1.f);
+    if (plane->Position->Axis) {
+        ConvertDirection(n, plane->Position->Axis.Get());
+    }
+    ConvertCartesianPoint(p, plane->Position->Location);
+
+    if (!IsTrue(hs->AgreementFlag)) {
+        n *= -1.f;
+    }
+
+    // clip the current contents of `meshout` against the plane we obtained from the second operand
+    const std::vector<IfcVector3> &in = first_operand.mVerts;
+    std::vector<IfcVector3> &outvert = result.mVerts;
+
+    std::vector<unsigned int>::const_iterator begin = first_operand.mVertcnt.begin(),
+                                              end = first_operand.mVertcnt.end(), iit;
+
+    outvert.reserve(in.size());
+    result.mVertcnt.reserve(first_operand.mVertcnt.size());
+
+    unsigned int vidx = 0;
+    for (iit = begin; iit != end; vidx += *iit++) {
+
+        unsigned int newcount = 0;
+        bool isAtWhiteSide = (in[vidx] - p) * n > -ai_epsilon;
+        for (unsigned int i = 0; i < *iit; ++i) {
+            const IfcVector3 &e0 = in[vidx + i], e1 = in[vidx + (i + 1) % *iit];
+
+            // does the next segment intersect the plane?
+            IfcVector3 isectpos;
+            if (IntersectSegmentPlane(p, n, e0, e1, isAtWhiteSide, isectpos)) {
+                if (isAtWhiteSide) {
+                    // e0 is on the right side, so keep it
+                    outvert.push_back(e0);
+                    outvert.push_back(isectpos);
+                    newcount += 2;
+                } else {
+                    // e0 is on the wrong side, so drop it and keep e1 instead
+                    outvert.push_back(isectpos);
+                    ++newcount;
+                }
+                isAtWhiteSide = !isAtWhiteSide;
+            } else {
+                if (isAtWhiteSide) {
+                    outvert.push_back(e0);
+                    ++newcount;
+                }
+            }
+        }
+
+        if (!newcount) {
+            continue;
+        }
+
+        IfcVector3 vmin, vmax;
+        ArrayBounds(&*(outvert.end() - newcount), newcount, vmin, vmax);
+
+        // filter our IfcFloat points - those may happen if a point lies
+        // directly on the intersection line. However, due to IfcFloat
+        // precision a bitwise comparison is not feasible to detect
+        // this case.
+        const IfcFloat epsilon = (vmax - vmin).SquareLength() / 1e6f;
+        FuzzyVectorCompare fz(epsilon);
+
+        std::vector<IfcVector3>::iterator e = std::unique(outvert.end() - newcount, outvert.end(), fz);
+
+        if (e != outvert.end()) {
+            newcount -= static_cast<unsigned int>(std::distance(e, outvert.end()));
+            outvert.erase(e, outvert.end());
+        }
+        if (fz(*(outvert.end() - newcount), outvert.back())) {
+            outvert.pop_back();
+            --newcount;
+        }
+        if (newcount > 2) {
+            result.mVertcnt.push_back(newcount);
+        } else
+            while (newcount-- > 0) {
+                result.mVerts.pop_back();
+            }
+    }
+    IFCImporter::LogVerboseDebug("generating CSG geometry by plane clipping (IfcBooleanClippingResult)");
+}
+
+// ------------------------------------------------------------------------------------------------
+// Check if e0-e1 intersects a sub-segment of the given boundary line.
+// note: this functions works on 3D vectors, but performs its intersection checks solely in xy.
+// New version takes the supposed inside/outside state as a parameter and treats corner cases as if
+// the line stays on that side. This should make corner cases more stable.
+// Two million assumptions! Boundary should have all z at 0.0, will be treated as closed, should not have
+// segments with length <1e-6, self-intersecting might break the corner case handling... just don't go there, ok?
+bool IntersectsBoundaryProfile(const IfcVector3 &e0, const IfcVector3 &e1, const std::vector<IfcVector3> &boundary,
+        const bool isStartAssumedInside, std::vector<std::pair<size_t, IfcVector3>> &intersect_results,
+        const bool halfOpen = false) {
+    ai_assert(intersect_results.empty());
+
+    // determine winding order - necessary to detect segments going "inwards" or "outwards" from a point directly on the border
+    // positive sum of angles means clockwise order when looking down the -Z axis
+    IfcFloat windingOrder = 0.0;
+    for (size_t i = 0, bcount = boundary.size(); i < bcount; ++i) {
+        IfcVector3 b01 = boundary[(i + 1) % bcount] - boundary[i];
+        IfcVector3 b12 = boundary[(i + 2) % bcount] - boundary[(i + 1) % bcount];
+        IfcVector3 b1_side = IfcVector3(b01.y, -b01.x, 0.0); // rotated 90° clockwise in Z plane
+        // Warning: rough estimate only. A concave poly with lots of small segments each featuring a small counter rotation
+        // could fool the accumulation. Correct implementation would be sum( acos( b01 * b2) * sign( b12 * b1_side))
+        windingOrder += (b1_side.x * b12.x + b1_side.y * b12.y);
+    }
+    windingOrder = windingOrder > 0.0 ? 1.0 : -1.0;
+
+    const IfcVector3 e = e1 - e0;
+
+    for (size_t i = 0, bcount = boundary.size(); i < bcount; ++i) {
+        // boundary segment i: b0-b1
+        const IfcVector3 &b0 = boundary[i];
+        const IfcVector3 &b1 = boundary[(i + 1) % bcount];
+        IfcVector3 b = b1 - b0;
+
+        // segment-segment intersection
+        // solve b0 + b*s = e0 + e*t for (s,t)
+        const IfcFloat det = (-b.x * e.y + e.x * b.y);
+        if (std::abs(det) < ai_epsilon) {
+            // no solutions (parallel lines)
+            continue;
+        }
+        IfcFloat b_sqlen_inv = 1.0 / b.SquareLength();
+
+        const IfcFloat x = b0.x - e0.x;
+        const IfcFloat y = b0.y - e0.y;
+        const IfcFloat s = (x * e.y - e.x * y) / det; // scale along boundary edge
+        const IfcFloat t = (x * b.y - b.x * y) / det; // scale along given segment
+        const IfcVector3 p = e0 + e * t;
+#ifdef ASSIMP_BUILD_DEBUG
+        const IfcVector3 check = b0 + b * s - p;
+        ai_assert((IfcVector2(check.x, check.y)).SquareLength() < 1e-5);
+#endif
+
+        // also calculate the distance of e0 and e1 to the segment. We need to detect the "starts directly on segment"
+        // and "ends directly at segment" cases
+        bool startsAtSegment, endsAtSegment;
+        {
+            // calculate closest point to each end on the segment, clamp that point to the segment's length, then check
+            // distance to that point. This approach is like testing if e0 is inside a capped cylinder.
+            IfcFloat et0 = (b.x * (e0.x - b0.x) + b.y * (e0.y - b0.y)) * b_sqlen_inv;
+            IfcVector3 closestPosToE0OnBoundary = b0 + std::max(IfcFloat(0.0), std::min(IfcFloat(1.0), et0)) * b;
+            startsAtSegment = (closestPosToE0OnBoundary - IfcVector3(e0.x, e0.y, 0.0)).SquareLength() < 1e-12;
+            IfcFloat et1 = (b.x * (e1.x - b0.x) + b.y * (e1.y - b0.y)) * b_sqlen_inv;
+            IfcVector3 closestPosToE1OnBoundary = b0 + std::max(IfcFloat(0.0), std::min(IfcFloat(1.0), et1)) * b;
+            endsAtSegment = (closestPosToE1OnBoundary - IfcVector3(e1.x, e1.y, 0.0)).SquareLength() < 1e-12;
+        }
+
+        // Line segment ends at boundary -> ignore any hit, it will be handled by possibly following segments
+        if (endsAtSegment && !halfOpen)
+            continue;
+
+        // Line segment starts at boundary -> generate a hit only if following that line would change the INSIDE/OUTSIDE
+        // state. This should catch the case where a connected set of segments has a point directly on the boundary,
+        // one segment not hitting it because it ends there and the next segment not hitting it because it starts there
+        // Should NOT generate a hit if the segment only touches the boundary but turns around and stays inside.
+        if (startsAtSegment) {
+            IfcVector3 inside_dir = IfcVector3(b.y, -b.x, 0.0) * windingOrder;
+            bool isGoingInside = (inside_dir * e) > 0.0;
+            if (isGoingInside == isStartAssumedInside)
+                continue;
+
+            // only insert the point into the list if it is sufficiently far away from the previous intersection point.
+            // This way, we avoid duplicate detection if the intersection is directly on the vertex between two segments.
+            if (!intersect_results.empty() && intersect_results.back().first == i - 1) {
+                const IfcVector3 diff = intersect_results.back().second - e0;
+                if (IfcVector2(diff.x, diff.y).SquareLength() < 1e-10)
+                    continue;
+            }
+            intersect_results.push_back(std::make_pair(i, e0));
+            continue;
+        }
+
+        // for a valid intersection, s and t should be in range [0,1]. Including a bit of epsilon on s, potential double
+        // hits on two consecutive boundary segments are filtered
+        if (s >= -ai_epsilon * b_sqlen_inv && s <= 1.0 + ai_epsilon * b_sqlen_inv && t >= 0.0 && (t <= 1.0 || halfOpen)) {
+            // only insert the point into the list if it is sufficiently far away from the previous intersection point.
+            // This way, we avoid duplicate detection if the intersection is directly on the vertex between two segments.
+            if (!intersect_results.empty() && intersect_results.back().first == i - 1) {
+                const IfcVector3 diff = intersect_results.back().second - p;
+                if (IfcVector2(diff.x, diff.y).SquareLength() < 1e-10)
+                    continue;
+            }
+            intersect_results.push_back(std::make_pair(i, p));
+        }
+    }
+
+    return !intersect_results.empty();
+}
+
+// ------------------------------------------------------------------------------------------------
+// note: this functions works on 3D vectors, but performs its intersection checks solely in xy.
+bool PointInPoly(const IfcVector3 &p, const std::vector<IfcVector3> &boundary) {
+    // even-odd algorithm: take a random vector that extends from p to infinite
+    // and counts how many times it intersects edges of the boundary.
+    // because checking for segment intersections is prone to numeric inaccuracies
+    // or double detections (i.e. when hitting multiple adjacent segments at their
+    // shared vertices) we do it thrice with different rays and vote on it.
+
+    // the even-odd algorithm doesn't work for points which lie directly on
+    // the border of the polygon. If any of our attempts produces this result,
+    // we return false immediately.
+
+    std::vector<std::pair<size_t, IfcVector3>> intersected_boundary;
+    size_t votes = 0;
+
+    IntersectsBoundaryProfile(p, p + IfcVector3(1.0, 0, 0), boundary, true, intersected_boundary, true);
+    votes += intersected_boundary.size() % 2;
+
+    intersected_boundary.clear();
+    IntersectsBoundaryProfile(p, p + IfcVector3(0, 1.0, 0), boundary, true, intersected_boundary, true);
+    votes += intersected_boundary.size() % 2;
+
+    intersected_boundary.clear();
+    IntersectsBoundaryProfile(p, p + IfcVector3(0.6, -0.6, 0.0), boundary, true, intersected_boundary, true);
+    votes += intersected_boundary.size() % 2;
+
+    return votes > 1;
+}
+
+// ------------------------------------------------------------------------------------------------
+void ProcessPolygonalBoundedBooleanHalfSpaceDifference(const Schema_2x3::IfcPolygonalBoundedHalfSpace *hs, TempMesh &result,
+        const TempMesh &first_operand,
+        ConversionData &conv) {
+    ai_assert(hs != nullptr);
+
+    const Schema_2x3::IfcPlane *const plane = hs->BaseSurface->ToPtr<Schema_2x3::IfcPlane>();
+    if (!plane) {
+        IFCImporter::LogError("expected IfcPlane as base surface for the IfcHalfSpaceSolid");
+        return;
+    }
+
+    // extract plane base position vector and normal vector
+    IfcVector3 p, n(0.f, 0.f, 1.f);
+    if (plane->Position->Axis) {
+        ConvertDirection(n, plane->Position->Axis.Get());
+    }
+    ConvertCartesianPoint(p, plane->Position->Location);
+
+    if (!IsTrue(hs->AgreementFlag)) {
+        n *= -1.f;
+    }
+
+    n.Normalize();
+
+    // obtain the polygonal bounding volume
+    std::shared_ptr<TempMesh> profile = std::shared_ptr<TempMesh>(new TempMesh());
+    if (!ProcessCurve(hs->PolygonalBoundary, *profile.get(), conv)) {
+        IFCImporter::LogError("expected valid polyline for boundary of boolean halfspace");
+        return;
+    }
+
+    // determine winding order by calculating the normal.
+    IfcVector3 profileNormal = TempMesh::ComputePolygonNormal(profile->mVerts.data(), profile->mVerts.size());
+
+    IfcMatrix4 proj_inv;
+    ConvertAxisPlacement(proj_inv, hs->Position);
+
+    // and map everything into a plane coordinate space so all intersection
+    // tests can be done in 2D space.
+    IfcMatrix4 proj = proj_inv;
+    proj.Inverse();
+
+    // clip the current contents of `meshout` against the plane we obtained from the second operand
+    const std::vector<IfcVector3> &in = first_operand.mVerts;
+    std::vector<IfcVector3> &outvert = result.mVerts;
+    std::vector<unsigned int> &outvertcnt = result.mVertcnt;
+
+    outvert.reserve(in.size());
+    outvertcnt.reserve(first_operand.mVertcnt.size());
+
+    unsigned int vidx = 0;
+    std::vector<unsigned int>::const_iterator begin = first_operand.mVertcnt.begin();
+    std::vector<unsigned int>::const_iterator end = first_operand.mVertcnt.end();
+    std::vector<unsigned int>::const_iterator iit;
+    for (iit = begin; iit != end; vidx += *iit++) {
+        // Our new approach: we cut the poly along the plane, then we intersect the part on the black side of the plane
+        // against the bounding polygon. All the white parts, and the black part outside the boundary polygon, are kept.
+        std::vector<IfcVector3> whiteside, blackside;
+
+        {
+            const IfcVector3 *srcVertices = &in[vidx];
+            const size_t srcVtxCount = *iit;
+            if (srcVtxCount == 0)
+                continue;
+
+            IfcVector3 polyNormal = TempMesh::ComputePolygonNormal(srcVertices, srcVtxCount, true);
+
+            // if the poly is parallel to the plane, put it completely on the black or white side
+            if (std::abs(polyNormal * n) > 0.9999) {
+                bool isOnWhiteSide = (srcVertices[0] - p) * n > -ai_epsilon;
+                std::vector<IfcVector3> &targetSide = isOnWhiteSide ? whiteside : blackside;
+                targetSide.insert(targetSide.end(), srcVertices, srcVertices + srcVtxCount);
+            } else {
+                // otherwise start building one polygon for each side. Whenever the current line segment intersects the plane
+                // we put a point there as an end of the current segment. Then we switch to the other side, put a point there, too,
+                // as a beginning of the current segment, and simply continue accumulating vertices.
+                bool isCurrentlyOnWhiteSide = ((srcVertices[0]) - p) * n > -ai_epsilon;
+                for (size_t a = 0; a < srcVtxCount; ++a) {
+                    IfcVector3 e0 = srcVertices[a];
+                    IfcVector3 e1 = srcVertices[(a + 1) % srcVtxCount];
+                    IfcVector3 ei;
+
+                    // put starting point to the current mesh
+                    std::vector<IfcVector3> &trgt = isCurrentlyOnWhiteSide ? whiteside : blackside;
+                    trgt.push_back(srcVertices[a]);
+
+                    // if there's an intersection, put an end vertex there, switch to the other side's mesh,
+                    // and add a starting vertex there, too
+                    bool isPlaneHit = IntersectSegmentPlane(p, n, e0, e1, isCurrentlyOnWhiteSide, ei);
+                    if (isPlaneHit) {
+                        if (trgt.empty() || (trgt.back() - ei).SquareLength() > 1e-12)
+                            trgt.push_back(ei);
+                        isCurrentlyOnWhiteSide = !isCurrentlyOnWhiteSide;
+                        std::vector<IfcVector3> &newtrgt = isCurrentlyOnWhiteSide ? whiteside : blackside;
+                        newtrgt.push_back(ei);
+                    }
+                }
+            }
+        }
+
+        // the part on the white side can be written into the target mesh right away
+        WritePolygon(whiteside, result);
+
+        // The black part is the piece we need to get rid of, but only the part of it within the boundary polygon.
+        // So we now need to construct all the polygons that result from BlackSidePoly minus BoundaryPoly.
+        FilterPolygon(blackside);
+
+        // Complicated, II. We run along the polygon. a) When we're inside the boundary, we run on until we hit an
+        // intersection, which means we're leaving it. We then start a new out poly there. b) When we're outside the
+        // boundary, we start collecting vertices until we hit an intersection, then we run along the boundary until we hit
+        // an intersection, then we switch back to the poly and run on on this one again, and so on until we got a closed
+        // loop. Then we continue with the path we left to catch potential additional polys on the other side of the
+        // boundary as described in a)
+        if (!blackside.empty()) {
+            // poly edge index, intersection point, edge index in boundary poly
+            std::vector<std::tuple<size_t, IfcVector3, size_t>> intersections;
+            bool startedInside = PointInPoly(proj * blackside.front(), profile->mVerts);
+            bool isCurrentlyInside = startedInside;
+
+            std::vector<std::pair<size_t, IfcVector3>> intersected_boundary;
+
+            for (size_t a = 0; a < blackside.size(); ++a) {
+                const IfcVector3 e0 = proj * blackside[a];
+                const IfcVector3 e1 = proj * blackside[(a + 1) % blackside.size()];
+
+                intersected_boundary.clear();
+                IntersectsBoundaryProfile(e0, e1, profile->mVerts, isCurrentlyInside, intersected_boundary);
+                // sort the hits by distance from e0 to get the correct in/out/in sequence. Manually :-( I miss you, C++11.
+                if (intersected_boundary.size() > 1) {
+                    bool keepSorting = true;
+                    while (keepSorting) {
+                        keepSorting = false;
+                        for (size_t b = 0; b < intersected_boundary.size() - 1; ++b) {
+                            if ((intersected_boundary[b + 1].second - e0).SquareLength() < (intersected_boundary[b].second - e0).SquareLength()) {
+                                keepSorting = true;
+                                std::swap(intersected_boundary[b + 1], intersected_boundary[b]);
+                            }
+                        }
+                    }
+                }
+                // now add them to the list of intersections
+                for (size_t b = 0; b < intersected_boundary.size(); ++b)
+                    intersections.push_back(std::make_tuple(a, proj_inv * intersected_boundary[b].second, intersected_boundary[b].first));
+
+                // and calculate our new inside/outside state
+                if (intersected_boundary.size() & 1)
+                    isCurrentlyInside = !isCurrentlyInside;
+            }
+
+            // we got a list of in-out-combinations of intersections. That should be an even number of intersections, or
+            // we are facing a non-recoverable error.
+            if ((intersections.size() & 1) != 0) {
+                IFCImporter::LogWarn("Odd number of intersections, can't work with that. Omitting half space boundary check.");
+                continue;
+            }
+
+            if (intersections.size() > 1) {
+                // If we started outside, the first intersection is a out->in intersection. Cycle them so that it
+                // starts with an intersection leaving the boundary
+                if (!startedInside)
+                    for (size_t b = 0; b < intersections.size() - 1; ++b)
+                        std::swap(intersections[b], intersections[(b + intersections.size() - 1) % intersections.size()]);
+
+                // Filter pairs of out->in->out that lie too close to each other.
+                for (size_t a = 0; intersections.size() > 0 && a < intersections.size() - 1; /**/) {
+                    if ((std::get<1>(intersections[a]) - std::get<1>(intersections[(a + 1) % intersections.size()])).SquareLength() < 1e-10)
+                        intersections.erase(intersections.begin() + a, intersections.begin() + a + 2);
+                    else
+                        a++;
+                }
+                if (intersections.size() > 1 && (std::get<1>(intersections.back()) - std::get<1>(intersections.front())).SquareLength() < 1e-10) {
+                    intersections.pop_back();
+                    intersections.erase(intersections.begin());
+                }
+            }
+
+            // no intersections at all: either completely inside the boundary, so everything gets discarded, or completely outside.
+            // in the latter case we're implementional lost. I'm simply going to ignore this, so a large poly will not get any
+            // holes if the boundary is smaller and does not touch it anywhere.
+            if (intersections.empty()) {
+                // starting point was outside -> everything is outside the boundary -> nothing is clipped -> add black side
+                // to result mesh unchanged
+                if (!startedInside) {
+                    outvertcnt.push_back(static_cast<unsigned int>(blackside.size()));
+                    outvert.insert(outvert.end(), blackside.begin(), blackside.end());
+                    continue;
+                } else {
+                    // starting point was inside the boundary -> everything is inside the boundary -> nothing is spared from the
+                    // clipping -> nothing left to add to the result mesh
+                    continue;
+                }
+            }
+
+            // determine the direction in which we're marching along the boundary polygon. If the src poly is faced upwards
+            // and the boundary is also winded this way, we need to march *backwards* on the boundary.
+            const IfcVector3 polyNormal = IfcMatrix3(proj) * TempMesh::ComputePolygonNormal(blackside.data(), blackside.size());
+            bool marchBackwardsOnBoundary = (profileNormal * polyNormal) >= 0.0;
+
+            // Build closed loops from these intersections. Starting from an intersection leaving the boundary we
+            // walk along the polygon to the next intersection (which should be an IS entering the boundary poly).
+            // From there we walk along the boundary until we hit another intersection leaving the boundary,
+            // walk along the poly to the next IS and so on until we're back at the starting point.
+            // We remove every intersection we "used up", so any remaining intersection is the start of a new loop.
+            while (!intersections.empty()) {
+                std::vector<IfcVector3> resultpoly;
+                size_t currentIntersecIdx = 0;
+
+                while (true) {
+                    ai_assert(intersections.size() > currentIntersecIdx + 1);
+                    std::tuple<size_t, IfcVector3, size_t> currintsec = intersections[currentIntersecIdx + 0];
+                    std::tuple<size_t, IfcVector3, size_t> nextintsec = intersections[currentIntersecIdx + 1];
+                    intersections.erase(intersections.begin() + currentIntersecIdx, intersections.begin() + currentIntersecIdx + 2);
+
+                    // we start with an in->out intersection
+                    resultpoly.push_back(std::get<1>(currintsec));
+                    // climb along the polygon to the next intersection, which should be an out->in
+                    size_t numPolyPoints = (std::get<0>(currintsec) > std::get<0>(nextintsec) ? blackside.size() : 0) + std::get<0>(nextintsec) - std::get<0>(currintsec);
+                    for (size_t a = 1; a <= numPolyPoints; ++a)
+                        resultpoly.push_back(blackside[(std::get<0>(currintsec) + a) % blackside.size()]);
+                    // put the out->in intersection
+                    resultpoly.push_back(std::get<1>(nextintsec));
+
+                    // generate segments along the boundary polygon that lie in the poly's plane until we hit another intersection
+                    IfcVector3 startingPoint = proj * std::get<1>(nextintsec);
+                    size_t currentBoundaryEdgeIdx = (std::get<2>(nextintsec) + (marchBackwardsOnBoundary ? 1 : 0)) % profile->mVerts.size();
+                    size_t nextIntsecIdx = SIZE_MAX;
+                    while (nextIntsecIdx == SIZE_MAX) {
+                        IfcFloat t = 1e10;
+
+                        size_t nextBoundaryEdgeIdx = marchBackwardsOnBoundary ? (currentBoundaryEdgeIdx + profile->mVerts.size() - 1) : currentBoundaryEdgeIdx + 1;
+                        nextBoundaryEdgeIdx %= profile->mVerts.size();
+                        // vertices of the current boundary segments
+                        IfcVector3 currBoundaryPoint = profile->mVerts[currentBoundaryEdgeIdx];
+                        IfcVector3 nextBoundaryPoint = profile->mVerts[nextBoundaryEdgeIdx];
+                        // project the two onto the polygon
+                        if (std::abs(polyNormal.z) > 1e-5) {
+                            currBoundaryPoint.z = startingPoint.z + (currBoundaryPoint.x - startingPoint.x) * polyNormal.x / polyNormal.z + (currBoundaryPoint.y - startingPoint.y) * polyNormal.y / polyNormal.z;
+                            nextBoundaryPoint.z = startingPoint.z + (nextBoundaryPoint.x - startingPoint.x) * polyNormal.x / polyNormal.z + (nextBoundaryPoint.y - startingPoint.y) * polyNormal.y / polyNormal.z;
+                        }
+
+                        // build a direction that goes along the boundary border but lies in the poly plane
+                        IfcVector3 boundaryPlaneNormal = ((nextBoundaryPoint - currBoundaryPoint) ^ profileNormal).Normalize();
+                        IfcVector3 dirAtPolyPlane = (boundaryPlaneNormal ^ polyNormal).Normalize() * (marchBackwardsOnBoundary ? -1.0 : 1.0);
+                        // if we can project the direction to the plane, we can calculate a maximum marching distance along that dir
+                        // until we finish that boundary segment and continue on the next
+                        if (std::abs(polyNormal.z) > 1e-5) {
+                            t = std::min(t, (nextBoundaryPoint - startingPoint).Length());
+                        }
+
+                        // check if the direction hits the loop start - if yes, we got a poly to output
+                        IfcVector3 dirToThatPoint = proj * resultpoly.front() - startingPoint;
+                        IfcFloat tpt = dirToThatPoint * dirAtPolyPlane;
+                        if (tpt > -1e-6 && tpt <= t && (dirToThatPoint - tpt * dirAtPolyPlane).SquareLength() < 1e-10) {
+                            nextIntsecIdx = intersections.size(); // dirty hack to end marching along the boundary and signal the end of the loop
+                            t = tpt;
+                        }
+
+                        // also check if the direction hits any in->out intersections earlier. If we hit one, we can switch back
+                        // to marching along the poly border from that intersection point
+                        for (size_t a = 0; a < intersections.size(); a += 2) {
+                            dirToThatPoint = proj * std::get<1>(intersections[a]) - startingPoint;
+                            tpt = dirToThatPoint * dirAtPolyPlane;
+                            if (tpt > -1e-6 && tpt <= t && (dirToThatPoint - tpt * dirAtPolyPlane).SquareLength() < 1e-10) {
+                                nextIntsecIdx = a; // switch back to poly and march on from this in->out intersection
+                                t = tpt;
+                            }
+                        }
+
+                        // if we keep marching on the boundary, put the segment end point to the result poly and well... keep marching
+                        if (nextIntsecIdx == SIZE_MAX) {
+                            resultpoly.push_back(proj_inv * nextBoundaryPoint);
+                            currentBoundaryEdgeIdx = nextBoundaryEdgeIdx;
+                            startingPoint = nextBoundaryPoint;
+                        }
+
+                        // quick endless loop check
+                        if (resultpoly.size() > blackside.size() + profile->mVerts.size()) {
+                            IFCImporter::LogError("Encountered endless loop while clipping polygon against poly-bounded half space.");
+                            break;
+                        }
+                    }
+
+                    // we're back on the poly - if this is the intersection we started from, we got a closed loop.
+                    if (nextIntsecIdx >= intersections.size()) {
+                        break;
+                    }
+
+                    // otherwise it's another intersection. Continue marching from there.
+                    currentIntersecIdx = nextIntsecIdx;
+                }
+
+                WritePolygon(resultpoly, result);
+            }
+        }
+    }
+    IFCImporter::LogVerboseDebug("generating CSG geometry by plane clipping with polygonal bounding (IfcBooleanClippingResult)");
+}
+
+// ------------------------------------------------------------------------------------------------
+void ProcessBooleanExtrudedAreaSolidDifference(const Schema_2x3::IfcExtrudedAreaSolid *as, TempMesh &result,
+        const TempMesh &first_operand,
+        ConversionData &conv) {
+    ai_assert(as != nullptr);
+
+    // This case is handled by reduction to an instance of the quadrify() algorithm.
+    // Obviously, this won't work for arbitrarily complex cases. In fact, the first
+    // operand should be near-planar. Luckily, this is usually the case in Ifc
+    // buildings.
+
+    std::shared_ptr<TempMesh> meshtmp = std::shared_ptr<TempMesh>(new TempMesh());
+    ProcessExtrudedAreaSolid(*as, *meshtmp, conv, false);
+
+    std::vector<TempOpening> openings(1, TempOpening(as, IfcVector3(0, 0, 0), meshtmp, std::shared_ptr<TempMesh>()));
+
+    result = first_operand;
+
+    TempMesh temp;
+
+    std::vector<IfcVector3>::const_iterator vit = first_operand.mVerts.begin();
+    for (unsigned int pcount : first_operand.mVertcnt) {
+        temp.Clear();
+
+        temp.mVerts.insert(temp.mVerts.end(), vit, vit + pcount);
+        temp.mVertcnt.push_back(pcount);
+
+        // The algorithms used to generate mesh geometry sometimes
+        // spit out lines or other degenerates which must be
+        // filtered to avoid running into assertions later on.
+
+        // ComputePolygonNormal returns the Newell normal, so the
+        // length of the normal is the area of the polygon.
+        const IfcVector3 &normal = temp.ComputeLastPolygonNormal(false);
+        if (normal.SquareLength() < static_cast<IfcFloat>(1e-5)) {
+            IFCImporter::LogWarn("skipping degenerate polygon (ProcessBooleanExtrudedAreaSolidDifference)");
+            continue;
+        }
+
+        GenerateOpenings(openings, temp, false, true);
+        result.Append(temp);
+
+        vit += pcount;
+    }
+
+    IFCImporter::LogVerboseDebug("generating CSG geometry by geometric difference to a solid (IfcExtrudedAreaSolid)");
+}
+
+// ------------------------------------------------------------------------------------------------
+void ProcessBoolean(const Schema_2x3::IfcBooleanResult &boolean, TempMesh &result, ConversionData &conv) {
+    // supported CSG operations:
+    //   DIFFERENCE
+    if (const Schema_2x3::IfcBooleanResult *const clip = boolean.ToPtr<Schema_2x3::IfcBooleanResult>()) {
+        if (clip->Operator != "DIFFERENCE") {
+            IFCImporter::LogWarn("encountered unsupported boolean operator: ", (std::string)clip->Operator);
+            return;
+        }
+
+        // supported cases (1st operand):
+        //  IfcBooleanResult -- call ProcessBoolean recursively
+        //  IfcSweptAreaSolid -- obtain polygonal geometry first
+
+        // supported cases (2nd operand):
+        //  IfcHalfSpaceSolid -- easy, clip against plane
+        //  IfcExtrudedAreaSolid -- reduce to an instance of the quadrify() algorithm
+
+        const Schema_2x3::IfcHalfSpaceSolid *const hs = clip->SecondOperand->ResolveSelectPtr<Schema_2x3::IfcHalfSpaceSolid>(conv.db);
+        const Schema_2x3::IfcExtrudedAreaSolid *const as = clip->SecondOperand->ResolveSelectPtr<Schema_2x3::IfcExtrudedAreaSolid>(conv.db);
+        if (!hs && !as) {
+            IFCImporter::LogError("expected IfcHalfSpaceSolid or IfcExtrudedAreaSolid as second clipping operand");
+            return;
+        }
+
+        TempMesh first_operand;
+        if (const Schema_2x3::IfcBooleanResult *const op0 = clip->FirstOperand->ResolveSelectPtr<Schema_2x3::IfcBooleanResult>(conv.db)) {
+            ProcessBoolean(*op0, first_operand, conv);
+        } else if (const Schema_2x3::IfcSweptAreaSolid *const swept = clip->FirstOperand->ResolveSelectPtr<Schema_2x3::IfcSweptAreaSolid>(conv.db)) {
+            ProcessSweptAreaSolid(*swept, first_operand, conv);
+        } else {
+            IFCImporter::LogError("expected IfcSweptAreaSolid or IfcBooleanResult as first clipping operand");
+            return;
+        }
+
+        if (hs) {
+
+            const Schema_2x3::IfcPolygonalBoundedHalfSpace *const hs_bounded = clip->SecondOperand->ResolveSelectPtr<Schema_2x3::IfcPolygonalBoundedHalfSpace>(conv.db);
+            if (hs_bounded) {
+                ProcessPolygonalBoundedBooleanHalfSpaceDifference(hs_bounded, result, first_operand, conv);
+            } else {
+                ProcessBooleanHalfSpaceDifference(hs, result, first_operand, conv);
+            }
+        } else {
+            ProcessBooleanExtrudedAreaSolidDifference(as, result, first_operand, conv);
+        }
+    } else {
+        IFCImporter::LogWarn("skipping unknown IfcBooleanResult entity, type is ", boolean.GetClassName());
+    }
+}
+
+} // namespace IFC
+} // namespace Assimp
+
+#endif