assimp/code/AssetLib/IFC/IFCGeometry.cpp

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/// @file  IFCGeometry.cpp
/// @brief Geometry conversion and synthesis for IFC

#ifndef ASSIMP_BUILD_NO_IFC_IMPORTER
#include "IFCUtil.h"
#include "Common/PolyTools.h"
#include "PostProcessing/ProcessHelper.h"
#include "contrib/poly2tri/poly2tri/poly2tri.h"
#include "contrib/clipper/clipper.hpp"

#include <iterator>
#include <memory>
#include <utility>

namespace Assimp {
namespace IFC {

// ------------------------------------------------------------------------------------------------
bool ProcessPolyloop(const Schema_2x3::IfcPolyLoop& loop, TempMesh& meshout, ConversionData& /*conv*/) {
    size_t cnt = 0;
    for(const Schema_2x3::IfcCartesianPoint& c : loop.Polygon) {
        IfcVector3 tmp;
        ConvertCartesianPoint(tmp,c);

        meshout.mVerts.push_back(tmp);
        ++cnt;
    }

    meshout.mVertcnt.push_back(static_cast<unsigned int>(cnt));

    // zero- or one- vertex polyloops simply ignored
    if (meshout.mVertcnt.back() > 1) {
        return true;
    }

    if (meshout.mVertcnt.back()==1) {
        meshout.mVertcnt.pop_back();
        meshout.mVerts.pop_back();
    }
    return false;
}

// ------------------------------------------------------------------------------------------------
void ProcessPolygonBoundaries(TempMesh& result, const TempMesh& inmesh, size_t master_bounds = (size_t)-1) {
    // handle all trivial cases
    if(inmesh.mVertcnt.empty()) {
        return;
    }
    if(inmesh.mVertcnt.size() == 1) {
        result.Append(inmesh);
        return;
    }

    ai_assert(std::count(inmesh.mVertcnt.begin(), inmesh.mVertcnt.end(), 0u) == 0);

    typedef std::vector<unsigned int>::const_iterator face_iter;

    face_iter begin = inmesh.mVertcnt.begin(), end = inmesh.mVertcnt.end(), iit;
    std::vector<unsigned int>::const_iterator outer_polygon_it = end;

    // major task here: given a list of nested polygon boundaries (one of which
    // is the outer contour), reduce the triangulation task arising here to
    // one that can be solved using the "quadrulation" algorithm which we use
    // for pouring windows out of walls. The algorithm does not handle all
    // cases but at least it is numerically stable and gives "nice" triangles.

    // first compute normals for all polygons using Newell's algorithm
    // do not normalize 'normals', we need the original length for computing the polygon area
    std::vector<IfcVector3> normals;
    inmesh.ComputePolygonNormals(normals,false);

    // One of the polygons might be a IfcFaceOuterBound (in which case `master_bounds`
    // is its index). Sadly we can't rely on it, the docs say 'At most one of the bounds
    // shall be of the type IfcFaceOuterBound'
    IfcFloat area_outer_polygon = 1e-10f;
    if (master_bounds != (size_t)-1) {
        ai_assert(master_bounds < inmesh.mVertcnt.size());
        outer_polygon_it = begin + master_bounds;
    } else {
        for(iit = begin; iit != end; ++iit) {
            // find the polygon with the largest area and take it as the outer bound.
            IfcVector3& n = normals[std::distance(begin,iit)];
            const IfcFloat area = n.SquareLength();
            if (area > area_outer_polygon) {
                area_outer_polygon = area;
                outer_polygon_it = iit;
            }
        }
    }
	
    if (outer_polygon_it == end) {
		return;
	}

    const size_t outer_polygon_size = *outer_polygon_it;
    const IfcVector3& master_normal = normals[std::distance(begin, outer_polygon_it)];

    // Generate fake openings to meet the interface for the quadrulate
    // algorithm. It boils down to generating small boxes given the
    // inner polygon and the surface normal of the outer contour.
    // It is important that we use the outer contour's normal because
    // this is the plane onto which the quadrulate algorithm will
    // project the entire mesh.
    std::vector<TempOpening> fake_openings;
    fake_openings.reserve(inmesh.mVertcnt.size()-1);

    std::vector<IfcVector3>::const_iterator vit = inmesh.mVerts.begin(), outer_vit;

    for(iit = begin; iit != end; vit += *iit++) {
        if (iit == outer_polygon_it) {
            outer_vit = vit;
            continue;
        }

        // Filter degenerate polygons to keep them from causing trouble later on
        IfcVector3& n = normals[std::distance(begin,iit)];
        const IfcFloat area = n.SquareLength();
        if (area < 1e-5f) {
            IFCImporter::LogWarn("skipping degenerate polygon (ProcessPolygonBoundaries)");
            continue;
        }

        fake_openings.emplace_back();
        TempOpening& opening = fake_openings.back();

        opening.extrusionDir = master_normal;
        opening.solid = nullptr;

        opening.profileMesh = std::make_shared<TempMesh>();
        opening.profileMesh->mVerts.reserve(*iit);
        opening.profileMesh->mVertcnt.push_back(*iit);

        std::copy(vit, vit + *iit, std::back_inserter(opening.profileMesh->mVerts));
    }

    // fill a mesh with ONLY the main polygon
    TempMesh temp;
    temp.mVerts.reserve(outer_polygon_size);
    temp.mVertcnt.push_back(static_cast<unsigned int>(outer_polygon_size));
    std::copy(outer_vit, outer_vit+outer_polygon_size,
        std::back_inserter(temp.mVerts));

    GenerateOpenings(fake_openings, temp, false, false);
    result.Append(temp);
}

// ------------------------------------------------------------------------------------------------
void ProcessConnectedFaceSet(const Schema_2x3::IfcConnectedFaceSet& fset, TempMesh& result, ConversionData& conv)
{
    for(const Schema_2x3::IfcFace& face : fset.CfsFaces) {
        // size_t ob = -1, cnt = 0;
        TempMesh meshout;
        for(const Schema_2x3::IfcFaceBound& bound : face.Bounds) {

            if(const Schema_2x3::IfcPolyLoop* const polyloop = bound.Bound->ToPtr<Schema_2x3::IfcPolyLoop>()) {
                if(ProcessPolyloop(*polyloop, meshout,conv)) {
                    // The outer boundary is better determined by checking which
                    // polygon covers the largest area.
                }
            } else {
                IFCImporter::LogWarn("skipping unknown IfcFaceBound entity, type is ", bound.Bound->GetClassName());
                continue;
            }
        }
        ProcessPolygonBoundaries(result, meshout);
    }
}

// ------------------------------------------------------------------------------------------------
void ProcessRevolvedAreaSolid(const Schema_2x3::IfcRevolvedAreaSolid& solid, TempMesh& result, ConversionData& conv) {
    TempMesh meshout;

    // first read the profile description
    if(!ProcessProfile(*solid.SweptArea,meshout,conv) || meshout.mVerts.size()<=1) {
        return;
    }

    IfcVector3 axis, pos;
    ConvertAxisPlacement(axis,pos,solid.Axis);

    IfcMatrix4 tb0,tb1;
    IfcMatrix4::Translation(pos,tb0);
    IfcMatrix4::Translation(-pos,tb1);

    const std::vector<IfcVector3>& in = meshout.mVerts;
    const size_t size=in.size();

    bool has_area = solid.SweptArea->ProfileType == "AREA" && size>2;
    const IfcFloat max_angle = solid.Angle*conv.angle_scale;
    if(std::fabs(max_angle) < 1e-3) {
        if(has_area) {
            result = meshout;
        }
        return;
    }

    const unsigned int cnt_segments = 
        std::max(2u,static_cast<unsigned int>(conv.settings.cylindricalTessellation * std::fabs(max_angle)/AI_MATH_HALF_PI_F));
    const IfcFloat delta = max_angle/cnt_segments;

    has_area = has_area && std::fabs(max_angle) < AI_MATH_TWO_PI_F*0.99;

    result.mVerts.reserve(size*((cnt_segments+1)*4+(has_area?2:0)));
    result.mVertcnt.reserve(size*cnt_segments+2);

    IfcMatrix4 rot;
    rot = tb0 * IfcMatrix4::Rotation(delta,axis,rot) * tb1;

    size_t base = 0;
    std::vector<IfcVector3>& out = result.mVerts;

    // dummy data to simplify later processing
    for(size_t i = 0; i < size; ++i) {
        out.insert(out.end(),4,in[i]);
    }

    for(unsigned int seg = 0; seg < cnt_segments; ++seg) {
        for(size_t i = 0; i < size; ++i) {
            const size_t next = (i+1)%size;

            result.mVertcnt.push_back(4);
            const IfcVector3 base_0 = out[base+i*4+3],base_1 = out[base+next*4+3];

            out.push_back(base_0);
            out.push_back(base_1);
            out.push_back(rot*base_1);
            out.push_back(rot*base_0);
        }
        base += size*4;
    }

    out.erase(out.begin(),out.begin()+size*4);

    if(has_area) {
        // leave the triangulation of the profile area to the ear cutting
        // implementation in aiProcess_Triangulate - for now we just
        // feed in two huge polygons.
        base -= size*8;
        for(size_t i = size; i--; ) {
            out.push_back(out[base+i*4+3]);
        }
        for(size_t i = 0; i < size; ++i ) {
            out.push_back(out[i*4]);
        }
        result.mVertcnt.push_back(static_cast<unsigned int>(size));
        result.mVertcnt.push_back(static_cast<unsigned int>(size));
    }

    IfcMatrix4 trafo;
    ConvertAxisPlacement(trafo, solid.Position);

    result.Transform(trafo);
    IFCImporter::LogVerboseDebug("generate mesh procedurally by radial extrusion (IfcRevolvedAreaSolid)");
}

// ------------------------------------------------------------------------------------------------
void ProcessSweptDiskSolid(const Schema_2x3::IfcSweptDiskSolid &solid, 
        TempMesh& result, 
        ConversionData& conv) {
    const Curve* const curve = Curve::Convert(*solid.Directrix, conv);
    if(!curve) {
        IFCImporter::LogError("failed to convert Directrix curve (IfcSweptDiskSolid)");
        return;
    }

    const unsigned int cnt_segments = conv.settings.cylindricalTessellation;
    const IfcFloat deltaAngle = AI_MATH_TWO_PI/cnt_segments;

	TempMesh temp;
	curve->SampleDiscrete(temp, solid.StartParam, solid.EndParam);
	const std::vector<IfcVector3>& curve_points = temp.mVerts;

    const size_t samples = curve_points.size();

    result.mVerts.reserve(cnt_segments * samples * 4);
    result.mVertcnt.reserve((cnt_segments - 1) * samples);

    std::vector<IfcVector3> points;
    points.reserve(cnt_segments * samples);

    if(curve_points.empty()) {
        IFCImporter::LogWarn("curve evaluation yielded no points (IfcSweptDiskSolid)");
        return;
    }

    IfcVector3 current = curve_points[0];
    IfcVector3 previous = current;
    IfcVector3 next;

    IfcVector3 startvec;
    startvec.x = 1.0f;
    startvec.y = 1.0f;
    startvec.z = 1.0f;

    unsigned int last_dir = 0;

    // generate circles at the sweep positions
    for(size_t i = 0; i < samples; ++i) {

        if(i != samples - 1) {
            next = curve_points[i + 1];
        }

        // get a direction vector reflecting the approximate curvature (i.e. tangent)
        IfcVector3 d = (current-previous) + (next-previous);

        d.Normalize();

        // figure out an arbitrary point q so that (p-q) * d = 0,
        // try to maximize ||(p-q)|| * ||(p_last-q_last)||
        IfcVector3 q;
        bool take_any = false;

        for (unsigned int j = 0; j < 2; ++j, take_any = true) {
            if ((last_dir == 0 || take_any) && std::abs(d.x) > ai_epsilon) {
                q.y = startvec.y;
                q.z = startvec.z;
                q.x = -(d.y * q.y + d.z * q.z) / d.x;
                last_dir = 0;
                break;
            } else if ((last_dir == 1 || take_any) && std::abs(d.y) > ai_epsilon) {
                q.x = startvec.x;
                q.z = startvec.z;
                q.y = -(d.x * q.x + d.z * q.z) / d.y;
                last_dir = 1;
                break;
            } else if ((last_dir == 2 && std::abs(d.z) > ai_epsilon) || take_any) {
                q.y = startvec.y;
                q.x = startvec.x;
                q.z = -(d.y * q.y + d.x * q.x) / d.z;
                last_dir = 2;
                break;
            }
        }

        q *= solid.Radius / q.Length();
        startvec = q;

        // generate a rotation matrix to rotate q around d
        IfcMatrix4 rot;
        IfcMatrix4::Rotation(deltaAngle,d,rot);

        for (unsigned int seg = 0; seg < cnt_segments; ++seg, q *= rot ) {
            points.push_back(q + current);
        }

        previous = current;
        current = next;
    }

    // make quads
    for(size_t i = 0; i < samples - 1; ++i) {

        const aiVector3D& this_start = points[ i * cnt_segments ];

        // locate corresponding point on next sample ring
        unsigned int best_pair_offset = 0;
        float best_distance_squared = 1e10f;
        for (unsigned int seg = 0; seg < cnt_segments; ++seg) {
            const aiVector3D& p = points[ (i+1) * cnt_segments + seg];
            const float l = (p-this_start).SquareLength();

            if(l < best_distance_squared) {
                best_pair_offset = seg;
                best_distance_squared = l;
            }
        }

        for (unsigned int seg = 0; seg < cnt_segments; ++seg) {

            result.mVerts.push_back(points[ i * cnt_segments + (seg % cnt_segments)]);
            result.mVerts.push_back(points[ i * cnt_segments + (seg + 1) % cnt_segments]);
            result.mVerts.push_back(points[ (i+1) * cnt_segments + ((seg + 1 + best_pair_offset) % cnt_segments)]);
            result.mVerts.push_back(points[ (i+1) * cnt_segments + ((seg + best_pair_offset) % cnt_segments)]);

            IfcVector3& v1 = *(result.mVerts.end()-1);
            IfcVector3& v2 = *(result.mVerts.end()-2);
            IfcVector3& v3 = *(result.mVerts.end()-3);
            IfcVector3& v4 = *(result.mVerts.end()-4);

            if (((v4-v3) ^ (v4-v1)) * (v4 - curve_points[i]) < 0.0f) {
                std::swap(v4, v1);
                std::swap(v3, v2);
            }

            result.mVertcnt.push_back(4);
        }
    }

    IFCImporter::LogVerboseDebug("generate mesh procedurally by sweeping a disk along a curve (IfcSweptDiskSolid)");
}

// ------------------------------------------------------------------------------------------------
IfcMatrix3 DerivePlaneCoordinateSpace(const TempMesh& curmesh, bool& ok, IfcVector3& norOut) {
    const std::vector<IfcVector3>& out = curmesh.mVerts;
    IfcMatrix3 m;

    ok = true;

    // The input "mesh" must be a single polygon
    const size_t s = out.size();
    ai_assert( curmesh.mVertcnt.size() == 1 );
    ai_assert( curmesh.mVertcnt.back() == s);

    const IfcVector3 any_point = out[s-1];
    IfcVector3 nor;

    // The input polygon is arbitrarily shaped, therefore we might need some tries
    // until we find a suitable normal. Note that Newell's algorithm would give
    // a more robust result, but this variant also gives us a suitable first
    // axis for the 2D coordinate space on the polygon plane, exploiting the
    // fact that the input polygon is nearly always a quad.
    bool done = false;
    size_t idx( 0 );
    for (size_t i = 0; !done && i < s-2; done || ++i) {
        idx = i;
        for (size_t j = i+1; j < s-1; ++j) {
            nor = -((out[i]-any_point)^(out[j]-any_point));
            if(std::fabs(nor.Length()) > 1e-8f) {
                done = true;
                break;
            }
        }
    }

    if(!done) {
        ok = false;
        return m;
    }

    nor.Normalize();
    norOut = nor;

    IfcVector3 r = (out[idx]-any_point);
    r.Normalize();

    // Reconstruct orthonormal basis
    // XXX use Gram Schmidt for increased robustness
    IfcVector3 u = r ^ nor;
    u.Normalize();

    m.a1 = r.x;
    m.a2 = r.y;
    m.a3 = r.z;

    m.b1 = u.x;
    m.b2 = u.y;
    m.b3 = u.z;

    m.c1 = -nor.x;
    m.c2 = -nor.y;
    m.c3 = -nor.z;

    return m;
}

const auto closeDistance = ai_epsilon;

bool areClose(Schema_2x3::IfcCartesianPoint pt1,Schema_2x3::IfcCartesianPoint pt2) {
    if(pt1.Coordinates.size() != pt2.Coordinates.size()) {
        IFCImporter::LogWarn("unable to compare differently-dimensioned points");
        return false;
    }
    auto coord1 = pt1.Coordinates.begin();
    auto coord2 = pt2.Coordinates.begin();
    // we're just testing each dimension separately rather than doing euclidean distance, as we're
    // looking for very close coordinates
    for(; coord1 != pt1.Coordinates.end(); coord1++,coord2++) {
        if(std::fabs(*coord1 - *coord2) > closeDistance) {
            return false;
        }
    }
    return true;
}

bool areClose(IfcVector3 pt1,IfcVector3 pt2) {
    return (std::fabs(pt1.x - pt2.x) < closeDistance &&
        std::fabs(pt1.y - pt2.y) < closeDistance &&
        std::fabs(pt1.z - pt2.z) < closeDistance);
}

// Extrudes the given polygon along the direction, converts it into an opening or applies all openings as necessary.
void ProcessExtrudedArea(const Schema_2x3::IfcExtrudedAreaSolid& solid, const TempMesh& curve,
    const IfcVector3& extrusionDir, TempMesh& result, ConversionData &conv, bool collect_openings)
{
    // Outline: 'curve' is now a list of vertex points forming the underlying profile, extrude along the given axis,
    // forming new triangles.
    const bool has_area = solid.SweptArea->ProfileType == "AREA" && curve.mVerts.size() > 2;
    if (solid.Depth < ai_epsilon) {
        if( has_area ) {
            result.Append(curve);
        }
        return;
    }

    result.mVerts.reserve(curve.mVerts.size()*(has_area ? 4 : 2));
    result.mVertcnt.reserve(curve.mVerts.size() + 2);
    std::vector<IfcVector3> in = curve.mVerts;

    // First step: transform all vertices into the target coordinate space
    IfcMatrix4 trafo;
    ConvertAxisPlacement(trafo, solid.Position);

    IfcVector3 vmin, vmax;
    MinMaxChooser<IfcVector3>()(vmin, vmax);
    for(IfcVector3& v : in) {
        v *= trafo;

        vmin = std::min(vmin, v);
        vmax = std::max(vmax, v);
    }

    vmax -= vmin;
    const IfcFloat diag = vmax.Length();
    IfcVector3 dir = IfcMatrix3(trafo) * extrusionDir;

    // reverse profile polygon if it's winded in the wrong direction in relation to the extrusion direction
    IfcVector3 profileNormal = TempMesh::ComputePolygonNormal(in.data(), in.size());
    if( profileNormal * dir < 0.0 ) {
        std::reverse(in.begin(), in.end());
    }

    std::vector<IfcVector3> nors;
    const bool openings = !!conv.apply_openings && conv.apply_openings->size();

    // Compute the normal vectors for all opening polygons as a prerequisite
    // to TryAddOpenings_Poly2Tri()
    // XXX this belongs into the aforementioned function
    if( openings ) {

        if( !conv.settings.useCustomTriangulation ) {
            // it is essential to apply the openings in the correct spatial order. The direction
            // doesn't matter, but we would screw up if we started with e.g. a door in between
            // two windows.
            std::sort(conv.apply_openings->begin(), conv.apply_openings->end(), TempOpening::DistanceSorter(in[0]));
        }

        nors.reserve(conv.apply_openings->size());
        for(TempOpening& t : *conv.apply_openings) {
            TempMesh &bounds = *t.profileMesh;

            if( bounds.mVerts.size() <= 2 ) {
                nors.emplace_back();
                continue;
            }
            auto nor = ((bounds.mVerts[2] - bounds.mVerts[0]) ^ (bounds.mVerts[1] - bounds.mVerts[0])).Normalize();
            auto vI0 = bounds.mVertcnt[0];
            for(size_t faceI = 0; faceI < bounds.mVertcnt.size(); faceI++)
            {
                if(bounds.mVertcnt[faceI] >= 3) {
                    // do a check that this is at least parallel to the base plane
                    auto nor2 = ((bounds.mVerts[vI0 + 2] - bounds.mVerts[vI0]) ^ (bounds.mVerts[vI0 + 1] - bounds.mVerts[vI0])).Normalize();
                    if(!areClose(nor,nor2)) {
                        std::stringstream msg;
                        msg << "Face " << faceI << " is not parallel with face 0 - opening on entity " << solid.GetID();
                        IFCImporter::LogWarn(msg.str().c_str());
                    }
                }
            }
            nors.push_back(nor);
        }
    }


    TempMesh temp;
    TempMesh& curmesh = openings ? temp : result;
    std::vector<IfcVector3>& out = curmesh.mVerts;

    size_t sides_with_openings = 0;
    for( size_t i = 0; i < in.size(); ++i ) {
        const size_t next = (i + 1) % in.size();

        curmesh.mVertcnt.push_back(4);

        out.push_back(in[i]);
        out.push_back(in[next]);
        out.push_back(in[next] + dir);
        out.push_back(in[i] + dir);

        if( openings ) {
            if( (in[i] - in[next]).Length() > diag * 0.1 && GenerateOpenings(*conv.apply_openings, temp, true, true, dir) ) {
                ++sides_with_openings;
            }

            result.Append(temp);
            temp.Clear();
        }
    }

    if(openings) {
        for(TempOpening& opening : *conv.apply_openings) {
            if(!opening.wallPoints.empty()) {
                std::stringstream msg;
                msg << "failed to generate all window caps on ID " << (int)solid.GetID();
                IFCImporter::LogError(msg.str().c_str());
            }
            opening.wallPoints.clear();
        }
    }

    size_t sides_with_v_openings = 0;
    if(has_area) {

        for(size_t n = 0; n < 2; ++n) {
            if(n > 0) {
                for(size_t i = 0; i < in.size(); ++i)
                    out.push_back(in[i] + dir);
            } else {
                for(size_t i = in.size(); i--; )
                    out.push_back(in[i]);
            }

            curmesh.mVertcnt.push_back(static_cast<unsigned int>(in.size()));
            if(openings && in.size() > 2) {
                if(GenerateOpenings(*conv.apply_openings,temp,true,true,dir)) {
                    ++sides_with_v_openings;
                }

                result.Append(temp);
                temp.Clear();
            }
        }
    }

    if (openings && (sides_with_openings == 1 || sides_with_v_openings == 2)) {
        std::stringstream msg;
        msg << "failed to resolve all openings, presumably their topology is not supported by Assimp - ID " << solid.GetID() << " sides_with_openings " << sides_with_openings << " sides_with_v_openings " << sides_with_v_openings;
        IFCImporter::LogWarn(msg.str().c_str());
    }

    IFCImporter::LogVerboseDebug("generate mesh procedurally by extrusion (IfcExtrudedAreaSolid)");

    // If this is an opening element, store both the extruded mesh and the 2D profile mesh
    // it was created from. Return an empty mesh to the caller.
    if( collect_openings && !result.IsEmpty() ) {
        ai_assert(conv.collect_openings);
        std::shared_ptr<TempMesh> profile = std::shared_ptr<TempMesh>(new TempMesh());
        profile->Swap(result);

        std::shared_ptr<TempMesh> profile2D = std::shared_ptr<TempMesh>(new TempMesh());
        profile2D->mVerts.insert(profile2D->mVerts.end(), in.begin(), in.end());
        profile2D->mVertcnt.push_back(static_cast<unsigned int>(in.size()));
        conv.collect_openings->push_back(TempOpening(&solid, dir, std::move(profile), std::move(profile2D)));

        ai_assert(result.IsEmpty());
    }
}

// ------------------------------------------------------------------------------------------------
void ProcessExtrudedAreaSolid(const Schema_2x3::IfcExtrudedAreaSolid& solid, 
        TempMesh& result,
        ConversionData& conv, 
        bool collect_openings) {
    TempMesh meshout;

    // First read the profile description.
    if(!ProcessProfile(*solid.SweptArea,meshout,conv) || meshout.mVerts.size()<=1) {
        return;
    }

    IfcVector3 dir;
    ConvertDirection(dir,solid.ExtrudedDirection);
    dir *= solid.Depth;

    // Some profiles bring their own holes, for which we need to provide a container. This all is somewhat backwards,
    // and there's still so many corner cases uncovered - we really need a generic solution to all of this hole carving.
    std::vector<TempOpening> fisherPriceMyFirstOpenings;
    std::vector<TempOpening>* oldApplyOpenings = conv.apply_openings;
    if( const Schema_2x3::IfcArbitraryProfileDefWithVoids* const cprofile = solid.SweptArea->ToPtr<Schema_2x3::IfcArbitraryProfileDefWithVoids>() ) {
        if( !cprofile->InnerCurves.empty() ) {
            // read all inner curves and extrude them to form proper openings.
            std::vector<TempOpening>* oldCollectOpenings = conv.collect_openings;
            conv.collect_openings = &fisherPriceMyFirstOpenings;

            for (const Schema_2x3::IfcCurve* curve : cprofile->InnerCurves) {
                TempMesh curveMesh, tempMesh;
                ProcessCurve(*curve, curveMesh, conv);
                ProcessExtrudedArea(solid, curveMesh, dir, tempMesh, conv, true);
            }
            // and then apply those to the geometry we're about to generate
            conv.apply_openings = conv.collect_openings;
            conv.collect_openings = oldCollectOpenings;
        }
    }

    ProcessExtrudedArea(solid, meshout, dir, result, conv, collect_openings);
    conv.apply_openings = oldApplyOpenings;
}

// ------------------------------------------------------------------------------------------------
void ProcessSweptAreaSolid(const Schema_2x3::IfcSweptAreaSolid& swept, 
        TempMesh& meshout,
        ConversionData& conv) {
    if(const Schema_2x3::IfcExtrudedAreaSolid* const solid = swept.ToPtr<Schema_2x3::IfcExtrudedAreaSolid>()) {
        ProcessExtrudedAreaSolid(*solid,meshout,conv, !!conv.collect_openings);
    } else if(const Schema_2x3::IfcRevolvedAreaSolid* const rev = swept.ToPtr<Schema_2x3::IfcRevolvedAreaSolid>()) {
        ProcessRevolvedAreaSolid(*rev,meshout,conv);
    } else {
        IFCImporter::LogWarn("skipping unknown IfcSweptAreaSolid entity, type is ", swept.GetClassName());
    }
}

// ------------------------------------------------------------------------------------------------
bool ProcessGeometricItem(const Schema_2x3::IfcRepresentationItem& geo, 
        unsigned int matid, 
        std::set<unsigned int>& mesh_indices,
        ConversionData& conv) {
    bool fix_orientation = false;
    std::shared_ptr< TempMesh > meshtmp = std::make_shared<TempMesh>();
    if(const Schema_2x3::IfcShellBasedSurfaceModel* shellmod = geo.ToPtr<Schema_2x3::IfcShellBasedSurfaceModel>()) {
        for (const std::shared_ptr<const Schema_2x3::IfcShell> &shell : shellmod->SbsmBoundary) {
            try {
                const ::Assimp::STEP::EXPRESS::ENTITY& e = shell->To<::Assimp::STEP::EXPRESS::ENTITY>();
                const Schema_2x3::IfcConnectedFaceSet& fs = conv.db.MustGetObject(e).To<Schema_2x3::IfcConnectedFaceSet>();

                ProcessConnectedFaceSet(fs, *meshtmp, conv);
            } catch(std::bad_cast&) {
                IFCImporter::LogWarn("unexpected type error, IfcShell ought to inherit from IfcConnectedFaceSet");
            }
        }
        fix_orientation = true;
    } else  if(const Schema_2x3::IfcConnectedFaceSet* fset = geo.ToPtr<Schema_2x3::IfcConnectedFaceSet>()) {
        ProcessConnectedFaceSet(*fset, *meshtmp, conv);
        fix_orientation = true;
    } else  if(const Schema_2x3::IfcSweptAreaSolid* swept = geo.ToPtr<Schema_2x3::IfcSweptAreaSolid>()) {
        ProcessSweptAreaSolid(*swept, *meshtmp, conv);
    } else  if(const Schema_2x3::IfcSweptDiskSolid* disk = geo.ToPtr<Schema_2x3::IfcSweptDiskSolid>()) {
        ProcessSweptDiskSolid(*disk, *meshtmp, conv);
    } else if(const Schema_2x3::IfcManifoldSolidBrep* brep = geo.ToPtr<Schema_2x3::IfcManifoldSolidBrep>()) {
        ProcessConnectedFaceSet(brep->Outer, *meshtmp, conv);
        fix_orientation = true;
    } else if(const Schema_2x3::IfcFaceBasedSurfaceModel* surf = geo.ToPtr<Schema_2x3::IfcFaceBasedSurfaceModel>()) {
        for(const Schema_2x3::IfcConnectedFaceSet& fc : surf->FbsmFaces) {
            ProcessConnectedFaceSet(fc, *meshtmp, conv);
        }
        fix_orientation = true;
    } else  if(const Schema_2x3::IfcBooleanResult* boolean = geo.ToPtr<Schema_2x3::IfcBooleanResult>()) {
        ProcessBoolean(*boolean, *meshtmp, conv);
    } else if(geo.ToPtr<Schema_2x3::IfcBoundingBox>()) {
        // silently skip over bounding boxes
        return false;
    } else {
        std::stringstream toLog;
        toLog << "skipping unknown IfcGeometricRepresentationItem entity, type is " << geo.GetClassName() << " id is " << geo.GetID();
        IFCImporter::LogWarn(toLog.str().c_str());
        return false;
    }

    // Do we just collect openings for a parent element (i.e. a wall)?
    // In such a case, we generate the polygonal mesh as usual,
    // but attach it to a TempOpening instance which will later be applied
    // to the wall it pertains to.

    // Note: swep area solids are added in ProcessExtrudedAreaSolid(),
    // which returns an empty mesh.
    if(conv.collect_openings) {
        if (!meshtmp->IsEmpty()) {
            conv.collect_openings->push_back(TempOpening(geo.ToPtr<Schema_2x3::IfcSolidModel>(),
                IfcVector3(0,0,0),
                std::move(meshtmp),
                std::shared_ptr<TempMesh>()));
        }
        return true;
    }

    if (meshtmp->IsEmpty()) {
        return false;
    }

    meshtmp->RemoveAdjacentDuplicates();
    meshtmp->RemoveDegenerates();

    if(fix_orientation) {
//      meshtmp->FixupFaceOrientation();
    }

    aiMesh* const mesh = meshtmp->ToMesh();
    if(mesh) {
        mesh->mMaterialIndex = matid;
        mesh_indices.insert(static_cast<unsigned int>(conv.meshes.size()));
        conv.meshes.push_back(mesh);
        return true;
    }
    return false;
}

// ------------------------------------------------------------------------------------------------
void AssignAddedMeshes(std::set<unsigned int>& mesh_indices,aiNode* nd, ConversionData& /*conv*/) {
    if (!mesh_indices.empty()) {
		std::set<unsigned int>::const_iterator it = mesh_indices.cbegin();
		std::set<unsigned int>::const_iterator end = mesh_indices.cend();

        nd->mNumMeshes = static_cast<unsigned int>(mesh_indices.size());

        nd->mMeshes = new unsigned int[nd->mNumMeshes];
        for(unsigned int i = 0; it != end && i < nd->mNumMeshes; ++i, ++it) {
            nd->mMeshes[i] = *it;
        }
    }
}

// ------------------------------------------------------------------------------------------------
bool TryQueryMeshCache(const Schema_2x3::IfcRepresentationItem& item,
        std::set<unsigned int>& mesh_indices, 
        unsigned int mat_index,
        ConversionData& conv) {
    ConversionData::MeshCacheIndex idx(&item, mat_index);
    ConversionData::MeshCache::const_iterator it = conv.cached_meshes.find(idx);
    if (it != conv.cached_meshes.end()) {
        std::copy((*it).second.begin(),(*it).second.end(),std::inserter(mesh_indices, mesh_indices.end()));
        return true;
    }
    return false;
}

// ------------------------------------------------------------------------------------------------
void PopulateMeshCache(const Schema_2x3::IfcRepresentationItem& item,
        const std::set<unsigned int>& mesh_indices, 
        unsigned int mat_index,
        ConversionData& conv) {
    ConversionData::MeshCacheIndex idx(&item, mat_index);
    conv.cached_meshes[idx] = mesh_indices;
}

// ------------------------------------------------------------------------------------------------
bool ProcessRepresentationItem(const Schema_2x3::IfcRepresentationItem& item, 
        unsigned int matid,
        std::set<unsigned int>& mesh_indices,
        ConversionData& conv) {
    // determine material
    unsigned int localmatid = ProcessMaterials(item.GetID(), matid, conv, true);

    if (!TryQueryMeshCache(item,mesh_indices,localmatid,conv)) {
        if(ProcessGeometricItem(item,localmatid,mesh_indices,conv)) {
            if(mesh_indices.size()) {
                PopulateMeshCache(item,mesh_indices,localmatid,conv);
            }
        } else {
            return false;
        }
    }
    return true;
}


} // ! IFC
} // ! Assimp

#endif // ASSIMP_BUILD_NO_IFC_IMPORTER