assimp/code/IFCOpenings.cpp

/*
Open Asset Import Library (assimp)
----------------------------------------------------------------------

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*/

/** @file  IFCOpenings.cpp
 *  @brief Implements a subset of Ifc CSG operations for pouring 
  *    holes for windows and doors into walls.
 */

#include "AssimpPCH.h"

#ifndef ASSIMP_BUILD_NO_IFC_IMPORTER
#include "IFCUtil.h"
#include "PolyTools.h"
#include "ProcessHelper.h"

#include "../contrib/poly2tri/poly2tri/poly2tri.h"
#include "../contrib/clipper/clipper.hpp"

#include <iterator>

namespace Assimp {
	namespace IFC {

		using ClipperLib::ulong64;
		// XXX use full -+ range ...
		const ClipperLib::long64 max_ulong64 = 1518500249; // clipper.cpp / hiRange var

		//#define to_int64(p)  (static_cast<ulong64>( std::max( 0., std::min( static_cast<IfcFloat>((p)), 1.) ) * max_ulong64 ))
#define to_int64(p)  (static_cast<ulong64>(static_cast<IfcFloat>((p) ) * max_ulong64 ))
#define from_int64(p) (static_cast<IfcFloat>((p)) / max_ulong64)
#define one_vec (IfcVector2(static_cast<IfcFloat>(1.0),static_cast<IfcFloat>(1.0)))


		// fallback method to generate wall openings
		bool TryAddOpenings_Poly2Tri(const std::vector<TempOpening>& openings,const std::vector<IfcVector3>& nors, 
			TempMesh& curmesh);


typedef std::pair< IfcVector2, IfcVector2 > BoundingBox;
typedef std::map<IfcVector2,size_t,XYSorter> XYSortedField;


// ------------------------------------------------------------------------------------------------
void QuadrifyPart(const IfcVector2& pmin, const IfcVector2& pmax, XYSortedField& field, 
	const std::vector< BoundingBox >& bbs, 
	std::vector<IfcVector2>& out)
{
	if (!(pmin.x-pmax.x) || !(pmin.y-pmax.y)) {
		return;
	}

	IfcFloat xs = 1e10, xe = 1e10;	
	bool found = false;

	// Search along the x-axis until we find an opening
	XYSortedField::iterator start = field.begin();
	for(; start != field.end(); ++start) {
		const BoundingBox& bb = bbs[(*start).second];
		if(bb.first.x >= pmax.x) {
			break;
		} 

		if (bb.second.x > pmin.x && bb.second.y > pmin.y && bb.first.y < pmax.y) {
			xs = bb.first.x;
			xe = bb.second.x;
			found = true;
			break;
		}
	}

	if (!found) {
		// the rectangle [pmin,pend] is opaque, fill it
		out.push_back(pmin);
		out.push_back(IfcVector2(pmin.x,pmax.y));
		out.push_back(pmax);
		out.push_back(IfcVector2(pmax.x,pmin.y));
		return;
	}

	xs = std::max(pmin.x,xs);
	xe = std::min(pmax.x,xe);

	// see if there's an offset to fill at the top of our quad
	if (xs - pmin.x) {
		out.push_back(pmin);
		out.push_back(IfcVector2(pmin.x,pmax.y));
		out.push_back(IfcVector2(xs,pmax.y));
		out.push_back(IfcVector2(xs,pmin.y));
	}

	// search along the y-axis for all openings that overlap xs and our quad
	IfcFloat ylast = pmin.y;
	found = false;
	for(; start != field.end(); ++start) {
		const BoundingBox& bb = bbs[(*start).second];
		if (bb.first.x > xs || bb.first.y >= pmax.y) {
			break;
		}

		if (bb.second.y > ylast) {

			found = true;
			const IfcFloat ys = std::max(bb.first.y,pmin.y), ye = std::min(bb.second.y,pmax.y);
			if (ys - ylast > 0.0f) {
				QuadrifyPart( IfcVector2(xs,ylast), IfcVector2(xe,ys) ,field,bbs,out);
			}

			// the following are the window vertices

			/*wnd.push_back(IfcVector2(xs,ys));
			wnd.push_back(IfcVector2(xs,ye));
			wnd.push_back(IfcVector2(xe,ye));
			wnd.push_back(IfcVector2(xe,ys));*/
			ylast = ye;
		}
	}
	if (!found) {
		// the rectangle [pmin,pend] is opaque, fill it
		out.push_back(IfcVector2(xs,pmin.y));
		out.push_back(IfcVector2(xs,pmax.y));
		out.push_back(IfcVector2(xe,pmax.y));
		out.push_back(IfcVector2(xe,pmin.y));
		return;
	}
	if (ylast < pmax.y) {
		QuadrifyPart( IfcVector2(xs,ylast), IfcVector2(xe,pmax.y) ,field,bbs,out);
	}

	// now for the whole rest
	if (pmax.x-xe) {
		QuadrifyPart(IfcVector2(xe,pmin.y), pmax ,field,bbs,out);
	}
}

typedef std::vector<IfcVector2> Contour;
typedef std::vector<bool> SkipList; // should probably use int for performance reasons

struct ProjectedWindowContour
{
	Contour contour;
	BoundingBox bb;
	SkipList skiplist;
	bool is_rectangular;


	ProjectedWindowContour(const Contour& contour, const BoundingBox& bb, bool is_rectangular)
		: contour(contour)
		, bb(bb)
		, is_rectangular(is_rectangular)
	{}


	bool IsInvalid() const {
		return contour.empty();
	}

	void FlagInvalid() {
		contour.clear();
	}

	void PrepareSkiplist() {
		skiplist.resize(contour.size(),false);
	}
};

typedef std::vector< ProjectedWindowContour > ContourVector;

// ------------------------------------------------------------------------------------------------
bool BoundingBoxesOverlapping( const BoundingBox &ibb, const BoundingBox &bb ) 
{
	// count the '=' case as non-overlapping but as adjacent to each other
	return ibb.first.x < bb.second.x && ibb.second.x > bb.first.x &&
		ibb.first.y < bb.second.y && ibb.second.y > bb.first.y;
}

// ------------------------------------------------------------------------------------------------
bool IsDuplicateVertex(const IfcVector2& vv, const std::vector<IfcVector2>& temp_contour)
{
	// sanity check for duplicate vertices
	BOOST_FOREACH(const IfcVector2& cp, temp_contour) {
		if ((cp-vv).SquareLength() < 1e-5f) {
			return true;
		}
	}  
	return false;
}

// ------------------------------------------------------------------------------------------------
void ExtractVerticesFromClipper(const ClipperLib::Polygon& poly, std::vector<IfcVector2>& temp_contour, 
	bool filter_duplicates = false)
{
	temp_contour.clear();
	BOOST_FOREACH(const ClipperLib::IntPoint& point, poly) {
		IfcVector2 vv = IfcVector2( from_int64(point.X), from_int64(point.Y));
		vv = std::max(vv,IfcVector2());
		vv = std::min(vv,one_vec);

		if (!filter_duplicates || !IsDuplicateVertex(vv, temp_contour)) {
			temp_contour.push_back(vv);
		}
	}
}

// ------------------------------------------------------------------------------------------------
BoundingBox GetBoundingBox(const ClipperLib::Polygon& poly)
{
	IfcVector2 newbb_min, newbb_max;
	MinMaxChooser<IfcVector2>()(newbb_min, newbb_max);

	BOOST_FOREACH(const ClipperLib::IntPoint& point, poly) {
		IfcVector2 vv = IfcVector2( from_int64(point.X), from_int64(point.Y));

		// sanity rounding
		vv = std::max(vv,IfcVector2());
		vv = std::min(vv,one_vec);

		newbb_min = std::min(newbb_min,vv);
		newbb_max = std::max(newbb_max,vv);
	}
	return BoundingBox(newbb_min, newbb_max);
}

// ------------------------------------------------------------------------------------------------
void InsertWindowContours(const ContourVector& contours,
	const std::vector<TempOpening>& openings,
	TempMesh& curmesh)
{
	// fix windows - we need to insert the real, polygonal shapes into the quadratic holes that we have now
	for(size_t i = 0; i < contours.size();++i) {
		const BoundingBox& bb = contours[i].bb;
		const std::vector<IfcVector2>& contour = contours[i].contour;
		if(contour.empty()) {
			continue;
		}

		// check if we need to do it at all - many windows just fit perfectly into their quadratic holes,
		// i.e. their contours *are* already their bounding boxes.
		if (contour.size() == 4) {
			std::set<IfcVector2,XYSorter> verts;
			for(size_t n = 0; n < 4; ++n) {
				verts.insert(contour[n]);
			}
			const std::set<IfcVector2,XYSorter>::const_iterator end = verts.end();
			if (verts.find(bb.first)!=end && verts.find(bb.second)!=end
				&& verts.find(IfcVector2(bb.first.x,bb.second.y))!=end 
				&& verts.find(IfcVector2(bb.second.x,bb.first.y))!=end 
				) {
					continue;
			}
		}

		const IfcFloat diag = (bb.first-bb.second).Length();
		const IfcFloat epsilon = diag/1000.f;

		// walk through all contour points and find those that lie on the BB corner
		size_t last_hit = -1, very_first_hit = -1;
		IfcVector2 edge;
		for(size_t n = 0, e=0, size = contour.size();; n=(n+1)%size, ++e) {

			// sanity checking
			if (e == size*2) {
				IFCImporter::LogError("encountered unexpected topology while generating window contour");
				break;
			}

			const IfcVector2& v = contour[n];

			bool hit = false;
			if (fabs(v.x-bb.first.x)<epsilon) {
				edge.x = bb.first.x;
				hit = true;
			}
			else if (fabs(v.x-bb.second.x)<epsilon) {
				edge.x = bb.second.x;
				hit = true;
			}

			if (fabs(v.y-bb.first.y)<epsilon) {
				edge.y = bb.first.y;
				hit = true;
			}
			else if (fabs(v.y-bb.second.y)<epsilon) {
				edge.y = bb.second.y;
				hit = true;
			}

			if (hit) {
				if (last_hit != (size_t)-1) {

					const size_t old = curmesh.verts.size();
					size_t cnt = last_hit > n ? size-(last_hit-n) : n-last_hit;
					for(size_t a = last_hit, e = 0; e <= cnt; a=(a+1)%size, ++e) {
						// hack: this is to fix cases where opening contours are self-intersecting.
						// Clipper doesn't produce such polygons, but as soon as we're back in
						// our brave new floating-point world, very small distances are consumed
						// by the maximum available precision, leading to self-intersecting
						// polygons. This fix makes concave windows fail even worse, but
						// anyway, fail is fail.
						if ((contour[a] - edge).SquareLength() > diag*diag*0.7) {
							continue;
						}
						curmesh.verts.push_back(IfcVector3(contour[a].x, contour[a].y, 0.0f));
					}

					if (edge != contour[last_hit]) {

						IfcVector2 corner = edge;

						if (fabs(contour[last_hit].x-bb.first.x)<epsilon) {
							corner.x = bb.first.x;
						}
						else if (fabs(contour[last_hit].x-bb.second.x)<epsilon) {
							corner.x = bb.second.x;
						}

						if (fabs(contour[last_hit].y-bb.first.y)<epsilon) {
							corner.y = bb.first.y;
						}
						else if (fabs(contour[last_hit].y-bb.second.y)<epsilon) {
							corner.y = bb.second.y;
						}

						curmesh.verts.push_back(IfcVector3(corner.x, corner.y, 0.0f));
					}
					else if (cnt == 1) {
						// avoid degenerate polygons (also known as lines or points)
						curmesh.verts.erase(curmesh.verts.begin()+old,curmesh.verts.end());
					}

					if (const size_t d = curmesh.verts.size()-old) {
						curmesh.vertcnt.push_back(d);
						std::reverse(curmesh.verts.rbegin(),curmesh.verts.rbegin()+d);
					}
					if (n == very_first_hit) {
						break;
					}
				}
				else {
					very_first_hit = n;
				}

				last_hit = n;
			}
		}
	}
}

// ------------------------------------------------------------------------------------------------
void MergeWindowContours (const std::vector<IfcVector2>& a, 
	const std::vector<IfcVector2>& b, 
	ClipperLib::ExPolygons& out) 
{
	out.clear();

	ClipperLib::Clipper clipper;
	ClipperLib::Polygon clip;

	BOOST_FOREACH(const IfcVector2& pip, a) {
		clip.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
	}

	if (ClipperLib::Orientation(clip)) {
		std::reverse(clip.begin(), clip.end());
	}

	clipper.AddPolygon(clip, ClipperLib::ptSubject);
	clip.clear();

	BOOST_FOREACH(const IfcVector2& pip, b) {
		clip.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
	}

	if (ClipperLib::Orientation(clip)) {
		std::reverse(clip.begin(), clip.end());
	}

	clipper.AddPolygon(clip, ClipperLib::ptSubject);
	clipper.Execute(ClipperLib::ctUnion, out,ClipperLib::pftNonZero,ClipperLib::pftNonZero);
}

// ------------------------------------------------------------------------------------------------
// Subtract a from b
void MakeDisjunctWindowContours (const std::vector<IfcVector2>& a, 
	const std::vector<IfcVector2>& b, 
	ClipperLib::ExPolygons& out) 
{
	out.clear();

	ClipperLib::Clipper clipper;
	ClipperLib::Polygon clip;

	BOOST_FOREACH(const IfcVector2& pip, a) {
		clip.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
	}

	if (ClipperLib::Orientation(clip)) {
		std::reverse(clip.begin(), clip.end());
	}

	clipper.AddPolygon(clip, ClipperLib::ptClip);
	clip.clear();

	BOOST_FOREACH(const IfcVector2& pip, b) {
		clip.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
	}

	if (ClipperLib::Orientation(clip)) {
		std::reverse(clip.begin(), clip.end());
	}

	clipper.AddPolygon(clip, ClipperLib::ptSubject);
	clipper.Execute(ClipperLib::ctDifference, out,ClipperLib::pftNonZero,ClipperLib::pftNonZero);
}

// ------------------------------------------------------------------------------------------------
void CleanupWindowContour(ProjectedWindowContour& window)
{
	std::vector<IfcVector2> scratch;
	std::vector<IfcVector2>& contour = window.contour;

	ClipperLib::Polygon subject;
	ClipperLib::Clipper clipper;
	ClipperLib::ExPolygons clipped;

	BOOST_FOREACH(const IfcVector2& pip, contour) {
		subject.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
	}

	clipper.AddPolygon(subject,ClipperLib::ptSubject);
	clipper.Execute(ClipperLib::ctUnion,clipped,ClipperLib::pftNonZero,ClipperLib::pftNonZero);

	// This should yield only one polygon or something went wrong 
	if (clipped.size() != 1) {

		// Empty polygon? drop the contour altogether
		if(clipped.empty()) {
			IFCImporter::LogError("error during polygon clipping, window contour is degenerate");
			window.FlagInvalid();
			return;
		}

		// Else: take the first only
		IFCImporter::LogError("error during polygon clipping, window contour is not convex");
	}

	ExtractVerticesFromClipper(clipped[0].outer, scratch);
	// Assume the bounding box doesn't change during this operation
}

// ------------------------------------------------------------------------------------------------
void CleanupWindowContours(ContourVector& contours)
{
	// Use PolyClipper to clean up window contours
	try {
		BOOST_FOREACH(ProjectedWindowContour& window, contours) {
			CleanupWindowContour(window);
		}
	}
	catch (const char* sx) {
		IFCImporter::LogError("error during polygon clipping, window shape may be wrong: (Clipper: " 
			+ std::string(sx) + ")");
	}
}

// ------------------------------------------------------------------------------------------------
void CleanupOuterContour(const std::vector<IfcVector2>& contour_flat, TempMesh& curmesh)
{
	std::vector<IfcVector3> vold;
	std::vector<unsigned int> iold;

	vold.reserve(curmesh.verts.size());
	iold.reserve(curmesh.vertcnt.size());

	// Fix the outer contour using polyclipper
	try {

		ClipperLib::Polygon subject;
		ClipperLib::Clipper clipper;
		ClipperLib::ExPolygons clipped;

		ClipperLib::Polygon clip;
		clip.reserve(contour_flat.size());
		BOOST_FOREACH(const IfcVector2& pip, contour_flat) {
			clip.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
		}

		if (!ClipperLib::Orientation(clip)) {
			std::reverse(clip.begin(), clip.end());
		}

		// We need to run polyclipper on every single polygon -- we can't run it one all
		// of them at once or it would merge them all together which would undo all
		// previous steps
		subject.reserve(4);
		size_t index = 0;
		size_t countdown = 0;
		BOOST_FOREACH(const IfcVector3& pip, curmesh.verts) {
			if (!countdown) {
				countdown = curmesh.vertcnt[index++];
				if (!countdown) {
					continue;
				}
			}
			subject.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
			if (--countdown == 0) {
				if (!ClipperLib::Orientation(subject)) {
					std::reverse(subject.begin(), subject.end());
				}

				clipper.AddPolygon(subject,ClipperLib::ptSubject);
				clipper.AddPolygon(clip,ClipperLib::ptClip);

				clipper.Execute(ClipperLib::ctIntersection,clipped,ClipperLib::pftNonZero,ClipperLib::pftNonZero);

				BOOST_FOREACH(const ClipperLib::ExPolygon& ex, clipped) {
					iold.push_back(ex.outer.size());
					BOOST_FOREACH(const ClipperLib::IntPoint& point, ex.outer) {
						vold.push_back(IfcVector3(
							from_int64(point.X), 
							from_int64(point.Y),
							0.0f));
					}
				}

				subject.clear();
				clipped.clear();
				clipper.Clear();
			}
		}
	}
	catch (const char* sx) {
		IFCImporter::LogError("Ifc: error during polygon clipping, wall contour line may be wrong: (Clipper: " 
			+ std::string(sx) + ")");

		return;
	}

	// swap data arrays
	std::swap(vold,curmesh.verts);
	std::swap(iold,curmesh.vertcnt);
}

typedef std::vector<TempOpening*> OpeningRefs;
typedef std::vector<OpeningRefs > OpeningRefVector;

typedef std::vector<std::pair<
	ContourVector::const_iterator, 
	Contour::const_iterator> 
> ContourRefVector; 

// ------------------------------------------------------------------------------------------------
bool BoundingBoxesAdjacent(const BoundingBox& bb, const BoundingBox& ibb)
{
	// TODO: I'm pretty sure there is a much more compact way to check this
	const IfcFloat epsilon = 1e-5f;
	return	(fabs(bb.second.x - ibb.first.x) < epsilon && bb.first.y <= ibb.second.y && bb.second.y >= ibb.first.y) ||
		(fabs(bb.first.x - ibb.second.x) < epsilon && ibb.first.y <= bb.second.y && ibb.second.y >= bb.first.y) || 
		(fabs(bb.second.y - ibb.first.y) < epsilon && bb.first.x <= ibb.second.x && bb.second.x >= ibb.first.x) ||
		(fabs(bb.first.y - ibb.second.y) < epsilon && ibb.first.x <= bb.second.x && ibb.second.x >= bb.first.x);
}

// ------------------------------------------------------------------------------------------------
// Check if m0,m1 intersects n0,n1 assuming same ordering of the points in the line segments
// output the intersection points on n0,n1
bool IntersectingLineSegments(const IfcVector2& n0, const IfcVector2& n1, 
	const IfcVector2& m0, const IfcVector2& m1,
	IfcVector2& out0, IfcVector2& out1)
{
	const IfcVector2& m0_to_m1 = m1 - m0;
	const IfcVector2& n0_to_n1 = n1 - n0;

	const IfcVector2& n0_to_m0 = m0 - n0;
	const IfcVector2& n1_to_m1 = m1 - n1;

	const IfcVector2& n0_to_m1 = m1 - n0;

	const IfcFloat e = 1e-5f;
	const IfcFloat smalle = 1e-9f;

	static const IfcFloat inf = std::numeric_limits<IfcFloat>::infinity();

	if (!(n0_to_m0.SquareLength() < e*e || fabs(n0_to_m0 * n0_to_n1) / (n0_to_m0.Length() * n0_to_n1.Length()) > 1-1e-5 )) {
		return false;
	}

	if (!(n1_to_m1.SquareLength() < e*e || fabs(n1_to_m1 * n0_to_n1) / (n1_to_m1.Length() * n0_to_n1.Length()) > 1-1e-5 )) {
		return false;
	}

	IfcFloat s0;
	IfcFloat s1;

	// pick the axis with the higher absolute difference so the result
	// is more accurate. Since we cannot guarantee that the axis with
	// the higher absolute difference is big enough as to avoid
	// divisions by zero, the case 0/0 ~ infinity is detected and
	// handled separately.
	if(fabs(n0_to_n1.x) > fabs(n0_to_n1.y)) {
		s0 = n0_to_m0.x / n0_to_n1.x;
		s1 = n0_to_m1.x / n0_to_n1.x;

		if (fabs(s0) == inf && fabs(n0_to_m0.x) < smalle) {
			s0 = 0.;
		}
		if (fabs(s1) == inf && fabs(n0_to_m1.x) < smalle) {
			s1 = 0.;
		}
	}
	else {
		s0 = n0_to_m0.y / n0_to_n1.y;
		s1 = n0_to_m1.y / n0_to_n1.y;

		if (fabs(s0) == inf && fabs(n0_to_m0.y) < smalle) {
			s0 = 0.;
		}
		if (fabs(s1) == inf && fabs(n0_to_m1.y) < smalle) {
			s1 = 0.;
		}
	}

	if (s1 < s0) {
		std::swap(s1,s0);
	}

	s0 = std::max(0.0,s0);
	s1 = std::max(0.0,s1);

	s0 = std::min(1.0,s0);
	s1 = std::min(1.0,s1);

	if (fabs(s1-s0) < e) {
		return false;
	}

	out0 = n0 + s0 * n0_to_n1;
	out1 = n0 + s1 * n0_to_n1;

	return true;
}

// ------------------------------------------------------------------------------------------------
void FindAdjacentContours(ContourVector::iterator current, const ContourVector& contours)
{
	const IfcFloat sqlen_epsilon = static_cast<IfcFloat>(1e-8);
	const BoundingBox& bb = (*current).bb;

	// What is to be done here is to populate the skip lists for the contour
	// and to add necessary padding points when needed.
	SkipList& skiplist = (*current).skiplist;

	// First step to find possible adjacent contours is to check for adjacent bounding
	// boxes. If the bounding boxes are not adjacent, the contours lines cannot possibly be.
	for (ContourVector::const_iterator it = contours.begin(), end = contours.end(); it != end; ++it) {
		if ((*it).IsInvalid()) {
			continue;
		}

		// this left here to make clear we also run on the current contour
		// to check for overlapping contour segments (which can happen due
		// to projection artifacts).
		//if(it == current) {
		//	continue;
		//}

		const bool is_me = it == current;

		const BoundingBox& ibb = (*it).bb;

		// Assumption: the bounding boxes are pairwise disjoint or identical
		ai_assert(is_me || !BoundingBoxesOverlapping(bb, ibb));

		if (is_me || BoundingBoxesAdjacent(bb, ibb)) {

			// Now do a each-against-everyone check for intersecting contour
			// lines. This obviously scales terribly, but in typical real
			// world Ifc files it will not matter since most windows that
			// are adjacent to each others are rectangular anyway.

			Contour& ncontour = (*current).contour;
			const Contour& mcontour = (*it).contour;

			for (size_t n = 0; n < ncontour.size(); ++n) {
				const IfcVector2& n0 = ncontour[n];
				const IfcVector2& n1 = ncontour[(n+1) % ncontour.size()];

				for (size_t m = 0, mend = (is_me ? n : mcontour.size()); m < mend; ++m) {
					ai_assert(&mcontour != &ncontour || m < n);

					const IfcVector2& m0 = mcontour[m];
					const IfcVector2& m1 = mcontour[(m+1) % mcontour.size()];

					IfcVector2 isect0, isect1;
					if (IntersectingLineSegments(n0,n1, m0, m1, isect0, isect1)) {

						if ((isect0 - n0).SquareLength() > sqlen_epsilon) {
							++n;

							ncontour.insert(ncontour.begin() + n, isect0);	
							skiplist.insert(skiplist.begin() + n, true);
						}
						else {
							skiplist[n] = true;
						}

						if ((isect1 - n1).SquareLength() > sqlen_epsilon) {
							++n;

							ncontour.insert(ncontour.begin() + n, isect1);
							skiplist.insert(skiplist.begin() + n, false);
						}
					}
				}
			}
		}
	}
}

// ------------------------------------------------------------------------------------------------
AI_FORCE_INLINE bool LikelyBorder(const IfcVector2& vdelta)
{
	const IfcFloat dot_point_epsilon = static_cast<IfcFloat>(1e-5);
	return fabs(vdelta.x * vdelta.y) < dot_point_epsilon;
}

// ------------------------------------------------------------------------------------------------
void FindBorderContours(ContourVector::iterator current)
{
	const IfcFloat border_epsilon_upper = static_cast<IfcFloat>(1-1e-4);
	const IfcFloat border_epsilon_lower = static_cast<IfcFloat>(1e-4);

	bool outer_border = false;
	bool start_on_outer_border = false;

	SkipList& skiplist = (*current).skiplist;
	IfcVector2 last_proj_point;

	const Contour::const_iterator cbegin = (*current).contour.begin(), cend = (*current).contour.end();

	for (Contour::const_iterator cit = cbegin; cit != cend; ++cit) {
		const IfcVector2& proj_point = *cit;

		// Check if this connection is along the outer boundary of the projection
		// plane. In such a case we better drop it because such 'edges' should
		// not have any geometry to close them (think of door openings).
		if (proj_point.x <= border_epsilon_lower || proj_point.x >= border_epsilon_upper ||
			proj_point.y <= border_epsilon_lower || proj_point.y >= border_epsilon_upper) {

				if (outer_border) {
					ai_assert(cit != cbegin);
					if (LikelyBorder(proj_point - last_proj_point)) {
						skiplist[std::distance(cbegin, cit) - 1] = true;
					}
				}
				else if (cit == cbegin) {
					start_on_outer_border = true;
				}
		
				outer_border = true;
		}
		else {
			outer_border = false;
		}

		last_proj_point = proj_point;
	}

	// handle last segment
	if (outer_border && start_on_outer_border) {
		const IfcVector2& proj_point = *cbegin;
		if (LikelyBorder(proj_point - last_proj_point)) {
			skiplist[skiplist.size()-1] = true;
		}
	}
}

// ------------------------------------------------------------------------------------------------
AI_FORCE_INLINE bool LikelyDiagonal(IfcVector2 vdelta)
{
	vdelta.x = fabs(vdelta.x);
	vdelta.y = fabs(vdelta.y);
	return (fabs(vdelta.x-vdelta.y) < 0.8 * std::max(vdelta.x, vdelta.y));
}

// ------------------------------------------------------------------------------------------------
void FindLikelyCrossingLines(ContourVector::iterator current)
{
	SkipList& skiplist = (*current).skiplist;
	IfcVector2 last_proj_point;

	const Contour::const_iterator cbegin = (*current).contour.begin(), cend = (*current).contour.end();
	for (Contour::const_iterator cit = cbegin; cit != cend; ++cit) {
		const IfcVector2& proj_point = *cit;

		if (cit != cbegin) {
			IfcVector2 vdelta = proj_point - last_proj_point;
			if (LikelyDiagonal(vdelta)) {
				skiplist[std::distance(cbegin, cit) - 1] = true;
			}
		} 

		last_proj_point = proj_point;
	}

	// handle last segment
	if (LikelyDiagonal(*cbegin - last_proj_point)) {
		skiplist[skiplist.size()-1] = true;
	}
}

// ------------------------------------------------------------------------------------------------
size_t CloseWindows(ContourVector& contours, 		  
	const IfcMatrix4& minv, 
	OpeningRefVector& contours_to_openings, 
	TempMesh& curmesh)
{
	size_t closed = 0;
	// For all contour points, check if one of the assigned openings does
	// already have points assigned to it. In this case, assume this is
	// the other side of the wall and generate connections between
	// the two holes in order to close the window. 

	// All this gets complicated by the fact that contours may pertain to
	// multiple openings(due to merging of adjacent or overlapping openings). 
	// The code is based on the assumption that this happens symmetrically
	// on both sides of the wall. If it doesn't (which would be a bug anyway)
	// wrong geometry may be generated.
	for (ContourVector::iterator it = contours.begin(), end = contours.end(); it != end; ++it) {
		if ((*it).IsInvalid()) {
			continue;
		}
		OpeningRefs& refs = contours_to_openings[std::distance(contours.begin(), it)];

		bool has_other_side = false;
		BOOST_FOREACH(const TempOpening* opening, refs) {
			if(!opening->wallPoints.empty()) {
				has_other_side = true;
				break;
			}
		}

		if (has_other_side) {

			ContourRefVector adjacent_contours;

			// prepare a skiplist for this contour. The skiplist is used to
			// eliminate unwanted contour lines for adjacent windows and
			// those bordering the outer frame.
			(*it).PrepareSkiplist();

			FindAdjacentContours(it, contours);
			FindBorderContours(it);

			// if the window is the result of a finite union or intersection of rectangles,
			// there shouldn't be any crossing or diagonal lines in it. Such lines would
			// be artifacts caused by numerical inaccuracies or other bugs in polyclipper
			// and our own code. Since rectangular openings are by far the most frequent
			// case, it is worth filtering for this corner case.
			if((*it).is_rectangular) {
				FindLikelyCrossingLines(it);
			}

			ai_assert((*it).skiplist.size() == (*it).contour.size());

			SkipList::const_iterator skipbegin = (*it).skiplist.begin(), skipend = (*it).skiplist.end();

			curmesh.verts.reserve(curmesh.verts.size() + (*it).contour.size() * 4);
			curmesh.vertcnt.reserve(curmesh.vertcnt.size() + (*it).contour.size());

			// XXX this algorithm is really a bit inefficient - both in terms
			// of constant factor and of asymptotic runtime.
			size_t vstart = curmesh.verts.size();
			std::vector<bool>::const_iterator skipit = skipbegin;

			IfcVector3 start0;
			IfcVector3 start1;

			IfcVector2 last_proj; 
			//const IfcVector2& first_proj; 

			const Contour::const_iterator cbegin = (*it).contour.begin(), cend = (*it).contour.end();

			bool drop_this_edge = false;
			for (Contour::const_iterator cit = cbegin; cit != cend; ++cit, drop_this_edge = *skipit++) {
				const IfcVector2& proj_point = *cit;

				// Locate the closest opposite point. This should be a good heuristic to
				// connect only the points that are really intended to be connected.
				IfcFloat best = static_cast<IfcFloat>(1e10);
				IfcVector3 bestv;

				/* debug code to check for unwanted diagonal lines in window contours
				if (cit != cbegin) {
					const IfcVector2& vdelta = proj_point - last_proj;
					if (fabs(vdelta.x-vdelta.y) < 0.5 * std::max(vdelta.x, vdelta.y)) {
						//continue;
					}
				} */

				const IfcVector3& world_point = minv * IfcVector3(proj_point.x,proj_point.y,0.0f);
				
				last_proj = proj_point;

				BOOST_FOREACH(const TempOpening* opening, refs) {
					BOOST_FOREACH(const IfcVector3& other, opening->wallPoints) {
						const IfcFloat sqdist = (world_point - other).SquareLength();
						
						if (sqdist < best) {
							// avoid self-connections
							if(sqdist < 1e-5) {
								continue;
							}

							bestv = other;
							best = sqdist;							
						}
					}
				}

				if (drop_this_edge) {
					curmesh.verts.pop_back();
					curmesh.verts.pop_back();
				}
				else {
					curmesh.verts.push_back(cit == cbegin ? world_point : bestv);
					curmesh.verts.push_back(cit == cbegin ? bestv : world_point);

					curmesh.vertcnt.push_back(4);
					++closed;
				}

				if (cit == cbegin) {
					start0 = world_point;
					start1 = bestv;
					continue;
				}

				curmesh.verts.push_back(world_point);
				curmesh.verts.push_back(bestv);

				if (cit == cend - 1) {
					drop_this_edge = *skipit;

					// Check if the final connection (last to first element) is itself
					// a border edge that needs to be dropped.
					if (drop_this_edge) {
						--closed;
						curmesh.vertcnt.pop_back();
						curmesh.verts.pop_back();
						curmesh.verts.pop_back();
					}
					else {
						curmesh.verts.push_back(start1);
						curmesh.verts.push_back(start0);
					}
				}
			}

			BOOST_FOREACH(TempOpening* opening, refs) {
				//opening->wallPoints.clear();
			}

		}
		else {
			
			const Contour::const_iterator cbegin = (*it).contour.begin(), cend = (*it).contour.end();
			BOOST_FOREACH(TempOpening* opening, refs) {
				ai_assert(opening->wallPoints.empty());
				opening->wallPoints.reserve(opening->wallPoints.capacity() + (*it).contour.size());
				for (Contour::const_iterator cit = cbegin; cit != cend; ++cit) {

					const IfcVector2& proj_point = *cit;
					opening->wallPoints.push_back(minv * IfcVector3(proj_point.x,proj_point.y,0.0f));
				}
			}
		}
	}
	return closed;
}

// ------------------------------------------------------------------------------------------------
void Quadrify(const std::vector< BoundingBox >& bbs, TempMesh& curmesh)
{
	ai_assert(curmesh.IsEmpty());

	std::vector<IfcVector2> quads;
	quads.reserve(bbs.size()*4);

	// sort openings by x and y axis as a preliminiary to the QuadrifyPart() algorithm
	XYSortedField field;
	for (std::vector<BoundingBox>::const_iterator it = bbs.begin(); it != bbs.end(); ++it) {
		if (field.find((*it).first) != field.end()) {
			IFCImporter::LogWarn("constraint failure during generation of wall openings, results may be faulty");
		}
		field[(*it).first] = std::distance(bbs.begin(),it);
	}

	QuadrifyPart(IfcVector2(),one_vec,field,bbs,quads);
	ai_assert(!(quads.size() % 4));

	curmesh.vertcnt.resize(quads.size()/4,4);
	curmesh.verts.reserve(quads.size());
	BOOST_FOREACH(const IfcVector2& v2, quads) {
		curmesh.verts.push_back(IfcVector3(v2.x, v2.y, static_cast<IfcFloat>(0.0)));
	}
}

// ------------------------------------------------------------------------------------------------
void Quadrify(const ContourVector& contours, TempMesh& curmesh)
{
	std::vector<BoundingBox> bbs;
	bbs.reserve(contours.size());

	BOOST_FOREACH(const ContourVector::value_type& val, contours) {
		bbs.push_back(val.bb);
	}

	Quadrify(bbs, curmesh);
}

// ------------------------------------------------------------------------------------------------
IfcMatrix4 ProjectOntoPlane(std::vector<IfcVector2>& out_contour, const TempMesh& in_mesh, 
	bool &ok, IfcVector3& nor_out)
{
	const std::vector<IfcVector3>& in_verts = in_mesh.verts;
	ok = true;

	IfcMatrix4 m = IfcMatrix4(DerivePlaneCoordinateSpace(in_mesh, ok, nor_out));
	if(!ok) {
		return IfcMatrix4();
	}
#ifdef _DEBUG
	const IfcFloat det = m.Determinant();
	ai_assert(fabs(det-1) < 1e-5);
#endif

	IfcFloat zcoord = 0;
	out_contour.reserve(in_verts.size());


	IfcVector3 vmin, vmax;
	MinMaxChooser<IfcVector3>()(vmin, vmax);

	// Project all points into the new coordinate system, collect min/max verts on the way
	BOOST_FOREACH(const IfcVector3& x, in_verts) {
		const IfcVector3& vv = m * x;
		// keep Z offset in the plane coordinate system. Ignoring precision issues
		// (which  are present, of course), this should be the same value for
		// all polygon vertices (assuming the polygon is planar).

		// XXX this should be guarded, but we somehow need to pick a suitable
		// epsilon
		// if(coord != -1.0f) {
		//	assert(fabs(coord - vv.z) < 1e-3f);
		// }
		zcoord += vv.z;
		vmin = std::min(vv, vmin);
		vmax = std::max(vv, vmax);

		out_contour.push_back(IfcVector2(vv.x,vv.y));
	}

	zcoord /= in_verts.size();

	// Further improve the projection by mapping the entire working set into
	// [0,1] range. This gives us a consistent data range so all epsilons
	// used below can be constants.
	vmax -= vmin;
	BOOST_FOREACH(IfcVector2& vv, out_contour) {
		vv.x  = (vv.x - vmin.x) / vmax.x;
		vv.y  = (vv.y - vmin.y) / vmax.y;

		// sanity rounding
		vv = std::max(vv,IfcVector2());
		vv = std::min(vv,one_vec);
	}

	IfcMatrix4 mult;
	mult.a1 = static_cast<IfcFloat>(1.0) / vmax.x;
	mult.b2 = static_cast<IfcFloat>(1.0) / vmax.y;

	mult.a4 = -vmin.x * mult.a1;
	mult.b4 = -vmin.y * mult.b2;
	mult.c4 = -zcoord;
	m = mult * m;

	// debug code to verify correctness
#ifdef _DEBUG
	std::vector<IfcVector2> out_contour2;
	BOOST_FOREACH(const IfcVector3& x, in_verts) {
		const IfcVector3& vv = m * x;

		out_contour2.push_back(IfcVector2(vv.x,vv.y));
		ai_assert(fabs(vv.z) < vmax.z + 1e-8);
	} 

	for(size_t i = 0; i < out_contour.size(); ++i) {
		ai_assert((out_contour[i]-out_contour2[i]).SquareLength() < 1e-6);
	}
#endif

	return m;
}

// ------------------------------------------------------------------------------------------------
bool GenerateOpenings(std::vector<TempOpening>& openings,
	const std::vector<IfcVector3>& nors, 
	TempMesh& curmesh,
	bool check_intersection,
	bool generate_connection_geometry,
	const IfcVector3& wall_extrusion_axis)
{
	std::vector<IfcVector3>& out = curmesh.verts;
	OpeningRefVector contours_to_openings;

	// Try to derive a solid base plane within the current surface for use as 
	// working coordinate system. Map all vertices onto this plane and 
	// rescale them to [0,1] range. This normalization means all further
	// epsilons need not be scaled.
	bool ok = true;

	std::vector<IfcVector2> contour_flat;

	IfcVector3 nor;
	const IfcMatrix4& m = ProjectOntoPlane(contour_flat, curmesh,  ok, nor);
	if(!ok) {
		return false;
	}

	// Obtain inverse transform for getting back to world space later on
	const IfcMatrix4 minv = IfcMatrix4(m).Inverse();

	// Compute bounding boxes for all 2D openings in projection space
	ContourVector contours;

	std::vector<IfcVector2> temp_contour;
	std::vector<IfcVector2> temp_contour2;

	IfcVector3 wall_extrusion_axis_norm = wall_extrusion_axis;
	wall_extrusion_axis_norm.Normalize();

	size_t c = 0;
	BOOST_FOREACH(TempOpening& opening,openings) {

		// extrusionDir may be 0,0,0 on case where the opening mesh is not an
		// IfcExtrudedAreaSolid but something else (i.e. a brep)
		IfcVector3 norm_extrusion_dir = opening.extrusionDir;
		if (norm_extrusion_dir.SquareLength() > 1e-10) {
			norm_extrusion_dir.Normalize();
		}
		else {
			norm_extrusion_dir = IfcVector3();
		}

		TempMesh* profile_data =  opening.profileMesh.get();
		bool is_2d_source = false;
		if (opening.profileMesh2D && norm_extrusion_dir.SquareLength() > 0) {
			
			if(fabs(norm_extrusion_dir * wall_extrusion_axis_norm) < 0.1) {
				// horizontal extrusion
				if (fabs(norm_extrusion_dir * nor) > 0.9) {
					profile_data = opening.profileMesh2D.get();
					is_2d_source = true;
				}
				else {
					//continue;
				}
			}
			else {
				// vertical extrusion
				if (fabs(norm_extrusion_dir * nor) > 0.9) {
					continue;
				}
				continue;
			}
		}
		std::vector<IfcVector3> profile_verts = profile_data->verts;
		std::vector<unsigned int> profile_vertcnts = profile_data->vertcnt;
		if(profile_verts.size() <= 2) {
			continue;	
		}	

		// The opening meshes are real 3D meshes so skip over all faces
		// clearly facing into the wrong direction. Also, we need to check
		// whether the meshes do actually intersect the base surface plane.
		// This is done by recording minimum and maximum values for the
		// d component of the plane equation for all polys and checking
		// against surface d.

		// Use the sign of the dot product of the face normal to the plane
		// normal to determine to which side of the difference mesh a
		// triangle belongs. Get independent bounding boxes and vertex
		// sets for both sides and take the better one (we can't just
		// take both - this would likely cause major screwup of vertex
		// winding, producing errors as late as in CloseWindows()).
		IfcFloat dmin, dmax;
		MinMaxChooser<IfcFloat>()(dmin,dmax);

		temp_contour.clear();
		temp_contour2.clear();

		IfcVector2 vpmin,vpmax;
		MinMaxChooser<IfcVector2>()(vpmin,vpmax);

		IfcVector2 vpmin2,vpmax2;
		MinMaxChooser<IfcVector2>()(vpmin2,vpmax2);

		for (size_t f = 0, vi_total = 0, fend = profile_vertcnts.size(); f < fend; ++f) {

			bool side_flag = true;
			if (!is_2d_source) {
				const IfcVector3& face_nor = ((profile_verts[vi_total+2] - profile_verts[vi_total]) ^
					(profile_verts[vi_total+1] - profile_verts[vi_total])).Normalize();

				const IfcFloat abs_dot_face_nor = abs(nor * face_nor);
				if (abs_dot_face_nor < 0.9) {
					vi_total += profile_vertcnts[f];
					continue;
				}

				side_flag = nor * face_nor > 0;
			}

			for (unsigned int vi = 0, vend = profile_vertcnts[f]; vi < vend; ++vi, ++vi_total) {
				const IfcVector3& x = profile_verts[vi_total];

				const IfcVector3& v = m * x;
				IfcVector2 vv(v.x, v.y);

				//if(check_intersection) {
					dmin = std::min(dmin, v.z);
					dmax = std::max(dmax, v.z);
				//}

				// sanity rounding
				vv = std::max(vv,IfcVector2());
				vv = std::min(vv,one_vec);

				if(side_flag) {
					vpmin = std::min(vpmin,vv);
					vpmax = std::max(vpmax,vv);
				}
				else {
					vpmin2 = std::min(vpmin2,vv);
					vpmax2 = std::max(vpmax2,vv);
				}

				std::vector<IfcVector2>& store = side_flag ? temp_contour : temp_contour2;

				if (!IsDuplicateVertex(vv, store)) {
					store.push_back(vv);
				}		
			}
		}

		if (temp_contour2.size() > 2) {
			ai_assert(!is_2d_source);
			const IfcVector2 area = vpmax-vpmin;
			const IfcVector2 area2 = vpmax2-vpmin2;
			if (temp_contour.size() <= 2 || fabs(area2.x * area2.y) > fabs(area.x * area.y)) {
				temp_contour.swap(temp_contour2);

				vpmax = vpmax2;
				vpmin = vpmin2;			
			}
		}
		if(temp_contour.size() <= 2) {
			continue;
		}

		// TODO: This epsilon may be too large
		const IfcFloat epsilon = fabs(dmax-dmin) * 0.0001;
		if (!is_2d_source && check_intersection && (0 < dmin-epsilon || 0 > dmax+epsilon)) {
			continue;
		}

		BoundingBox bb = BoundingBox(vpmin,vpmax);

		// Skip over very small openings - these are likely projection errors
		// (i.e. they don't belong to this side of the wall)
		if(fabs(vpmax.x - vpmin.x) * fabs(vpmax.y - vpmin.y) < static_cast<IfcFloat>(1e-10)) {
			continue;
		}
		std::vector<TempOpening*> joined_openings(1, &opening);

		bool is_rectangle = temp_contour.size() == 4;

		// See if this BB intersects or is in close adjacency to any other BB we have so far.
		for (ContourVector::iterator it = contours.begin(); it != contours.end(); ) {
			const BoundingBox& ibb = (*it).bb;

			if (BoundingBoxesOverlapping(ibb, bb)) {

				if (!(*it).is_rectangular) {
					is_rectangle = false;
				}

				const std::vector<IfcVector2>& other = (*it).contour;
				ClipperLib::ExPolygons poly;

				// First check whether subtracting the old contour (to which ibb belongs)
				// from the new contour (to which bb belongs) yields an updated bb which
				// no longer overlaps ibb
				MakeDisjunctWindowContours(other, temp_contour, poly);
				if(poly.size() == 1) {
					
					const BoundingBox& newbb = GetBoundingBox(poly[0].outer);
					if (!BoundingBoxesOverlapping(ibb, newbb )) {
						 // Good guy bounding box
						 bb = newbb ;

						 ExtractVerticesFromClipper(poly[0].outer, temp_contour, false);
						 continue;
					}
				}

				// Take these two overlapping contours and try to merge them. If they 
				// overlap (which should not happen, but in fact happens-in-the-real-
				// world [tm] ), resume using a single contour and a single bounding box.
				MergeWindowContours(temp_contour, other, poly);

				if (poly.size() > 1) { 
					return TryAddOpenings_Poly2Tri(openings, nors, curmesh);
				}
				else if (poly.size() == 0) {
					IFCImporter::LogWarn("ignoring duplicate opening");
					temp_contour.clear();
					break;
				}
				else {
					IFCImporter::LogDebug("merging overlapping openings");				
					ExtractVerticesFromClipper(poly[0].outer, temp_contour, false);

					// Generate the union of the bounding boxes
					bb.first = std::min(bb.first, ibb.first);
					bb.second = std::max(bb.second, ibb.second);

					// Update contour-to-opening tables accordingly
					if (generate_connection_geometry) {
						std::vector<TempOpening*>& t = contours_to_openings[std::distance(contours.begin(),it)]; 
						joined_openings.insert(joined_openings.end(), t.begin(), t.end());

						contours_to_openings.erase(contours_to_openings.begin() + std::distance(contours.begin(),it));
					}

					contours.erase(it);

					// Restart from scratch because the newly formed BB might now
					// overlap any other BB which its constituent BBs didn't
					// previously overlap.
					it = contours.begin();
					continue;
				}
			}
			++it;
		}

		if(!temp_contour.empty()) {
			if (generate_connection_geometry) {
				contours_to_openings.push_back(std::vector<TempOpening*>(
					joined_openings.begin(),
					joined_openings.end()));
			}

			contours.push_back(ProjectedWindowContour(temp_contour, bb, is_rectangle));
		}
	}

	// Check if we still have any openings left - it may well be that this is
	// not the cause, for example if all the opening candidates don't intersect
	// this surface or point into a direction perpendicular to it.
	if (contours.empty()) {
		return false;
	}

	curmesh.Clear();

	// Generate a base subdivision into quads to accommodate the given list
	// of window bounding boxes.
	Quadrify(contours,curmesh);

	// Run a sanity cleanup pass on the window contours to avoid generating
	// artifacts during the contour generation phase later on.
	CleanupWindowContours(contours);

	// Previously we reduced all windows to rectangular AABBs in projection
	// space, now it is time to fill the gaps between the BBs and the real
	// window openings.
	InsertWindowContours(contours,openings, curmesh);

	// Clip the entire outer contour of our current result against the real
	// outer contour of the surface. This is necessary because the result
	// of the Quadrify() algorithm is always a square area spanning
	// over [0,1]^2 (i.e. entire projection space).
	CleanupOuterContour(contour_flat, curmesh);

	// Undo the projection and get back to world (or local object) space
	BOOST_FOREACH(IfcVector3& v3, curmesh.verts) {
		v3 = minv * v3;
	}

	// Generate window caps to connect the symmetric openings on both sides
	// of the wall.
 	if (generate_connection_geometry) {
		CloseWindows(contours, minv, contours_to_openings, curmesh);
	}
	return true;
}

// ------------------------------------------------------------------------------------------------
bool TryAddOpenings_Poly2Tri(const std::vector<TempOpening>& openings,const std::vector<IfcVector3>& nors, 
	TempMesh& curmesh)
{
	IFCImporter::LogWarn("forced to use poly2tri fallback method to generate wall openings");
	std::vector<IfcVector3>& out = curmesh.verts;

	bool result = false;

	// Try to derive a solid base plane within the current surface for use as 
	// working coordinate system. 
	bool ok;
	IfcVector3 nor;
	const IfcMatrix3& m = DerivePlaneCoordinateSpace(curmesh, ok, nor);
	if (!ok) {
		return false;
	}

	const IfcMatrix3 minv = IfcMatrix3(m).Inverse();


	IfcFloat coord = -1;

	std::vector<IfcVector2> contour_flat;
	contour_flat.reserve(out.size());

	IfcVector2 vmin, vmax;
	MinMaxChooser<IfcVector2>()(vmin, vmax);
	
	// Move all points into the new coordinate system, collecting min/max verts on the way
	BOOST_FOREACH(IfcVector3& x, out) {
		const IfcVector3 vv = m * x;

		// keep Z offset in the plane coordinate system. Ignoring precision issues
		// (which  are present, of course), this should be the same value for
		// all polygon vertices (assuming the polygon is planar).


		// XXX this should be guarded, but we somehow need to pick a suitable
		// epsilon
		// if(coord != -1.0f) {
		//	assert(fabs(coord - vv.z) < 1e-3f);
		// }

		coord = vv.z;

		vmin = std::min(IfcVector2(vv.x, vv.y), vmin);
		vmax = std::max(IfcVector2(vv.x, vv.y), vmax);

		contour_flat.push_back(IfcVector2(vv.x,vv.y));
	}
		
	// With the current code in DerivePlaneCoordinateSpace, 
	// vmin,vmax should always be the 0...1 rectangle (+- numeric inaccuracies) 
	// but here we won't rely on this.

	vmax -= vmin;

	// If this happens then the projection must have been wrong.
	assert(vmax.Length());

	ClipperLib::ExPolygons clipped;
	ClipperLib::Polygons holes_union;


	IfcVector3 wall_extrusion;
	bool do_connections = false, first = true;

	try {

		ClipperLib::Clipper clipper_holes;
		size_t c = 0;

		BOOST_FOREACH(const TempOpening& t,openings) {
			const IfcVector3& outernor = nors[c++];
			const IfcFloat dot = nor * outernor;
			if (fabs(dot)<1.f-1e-6f) {
				continue;
			}

			const std::vector<IfcVector3>& va = t.profileMesh->verts;
			if(va.size() <= 2) {
				continue;	
			}
		
			std::vector<IfcVector2> contour;

			BOOST_FOREACH(const IfcVector3& xx, t.profileMesh->verts) {
				IfcVector3 vv = m *  xx, vv_extr = m * (xx + t.extrusionDir);
				
				const bool is_extruded_side = fabs(vv.z - coord) > fabs(vv_extr.z - coord);
				if (first) {
					first = false;
					if (dot > 0.f) {
						do_connections = true;
						wall_extrusion = t.extrusionDir;
						if (is_extruded_side) {
							wall_extrusion = - wall_extrusion;
						}
					}
				}

				// XXX should not be necessary - but it is. Why? For precision reasons?
				vv = is_extruded_side ? vv_extr : vv;
				contour.push_back(IfcVector2(vv.x,vv.y));
			}

			ClipperLib::Polygon hole;
			BOOST_FOREACH(IfcVector2& pip, contour) {
				pip.x  = (pip.x - vmin.x) / vmax.x;
				pip.y  = (pip.y - vmin.y) / vmax.y;

				hole.push_back(ClipperLib::IntPoint(  to_int64(pip.x), to_int64(pip.y) ));
			}

			if (!ClipperLib::Orientation(hole)) {
				std::reverse(hole.begin(), hole.end());
			//	assert(ClipperLib::Orientation(hole));
			}

			/*ClipperLib::Polygons pol_temp(1), pol_temp2(1);
			pol_temp[0] = hole;

			ClipperLib::OffsetPolygons(pol_temp,pol_temp2,5.0);
			hole = pol_temp2[0];*/

			clipper_holes.AddPolygon(hole,ClipperLib::ptSubject);
		}

		clipper_holes.Execute(ClipperLib::ctUnion,holes_union,
			ClipperLib::pftNonZero,
			ClipperLib::pftNonZero);

		if (holes_union.empty()) {
			return false;
		}

		// Now that we have the big union of all holes, subtract it from the outer contour
		// to obtain the final polygon to feed into the triangulator.
		{
			ClipperLib::Polygon poly;
			BOOST_FOREACH(IfcVector2& pip, contour_flat) {
				pip.x  = (pip.x - vmin.x) / vmax.x;
				pip.y  = (pip.y - vmin.y) / vmax.y;

				poly.push_back(ClipperLib::IntPoint( to_int64(pip.x), to_int64(pip.y) ));
			}

			if (ClipperLib::Orientation(poly)) {
				std::reverse(poly.begin(), poly.end());
			}
			clipper_holes.Clear();
			clipper_holes.AddPolygon(poly,ClipperLib::ptSubject);

			clipper_holes.AddPolygons(holes_union,ClipperLib::ptClip);
			clipper_holes.Execute(ClipperLib::ctDifference,clipped,
				ClipperLib::pftNonZero,
				ClipperLib::pftNonZero);
		}

	}
	catch (const char* sx) {
		IFCImporter::LogError("Ifc: error during polygon clipping, skipping openings for this face: (Clipper: " 
			+ std::string(sx) + ")");

		return false;
	}

	std::vector<IfcVector3> old_verts;
	std::vector<unsigned int> old_vertcnt;

	old_verts.swap(curmesh.verts);
	old_vertcnt.swap(curmesh.vertcnt);


	// add connection geometry to close the adjacent 'holes' for the openings
	// this should only be done from one side of the wall or the polygons 
	// would be emitted twice.
	if (false && do_connections) {

		std::vector<IfcVector3> tmpvec;
		BOOST_FOREACH(ClipperLib::Polygon& opening, holes_union) {

			assert(ClipperLib::Orientation(opening));

			tmpvec.clear();

			BOOST_FOREACH(ClipperLib::IntPoint& point, opening) {

				tmpvec.push_back( minv * IfcVector3(
					vmin.x + from_int64(point.X) * vmax.x, 
					vmin.y + from_int64(point.Y) * vmax.y,
					coord));
			}

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

				curmesh.vertcnt.push_back(4);

				const IfcVector3& in_world = tmpvec[i];
				const IfcVector3& next_world = tmpvec[next];

				// Assumptions: no 'partial' openings, wall thickness roughly the same across the wall
				curmesh.verts.push_back(in_world);
				curmesh.verts.push_back(in_world+wall_extrusion);
				curmesh.verts.push_back(next_world+wall_extrusion);
				curmesh.verts.push_back(next_world);
			}
		}
	}
	
	std::vector< std::vector<p2t::Point*> > contours;
	BOOST_FOREACH(ClipperLib::ExPolygon& clip, clipped) {
		
		contours.clear();

		// Build the outer polygon contour line for feeding into poly2tri
		std::vector<p2t::Point*> contour_points;
		BOOST_FOREACH(ClipperLib::IntPoint& point, clip.outer) {
			contour_points.push_back( new p2t::Point(from_int64(point.X), from_int64(point.Y)) );
		}

		p2t::CDT* cdt ;
		try {
			// Note: this relies on custom modifications in poly2tri to raise runtime_error's
			// instead if assertions. These failures are not debug only, they can actually
			// happen in production use if the input data is broken. An assertion would be
			// inappropriate.
			cdt = new p2t::CDT(contour_points);
		}
		catch(const std::exception& e) {
			IFCImporter::LogError("Ifc: error during polygon triangulation, skipping some openings: (poly2tri: " 
				+ std::string(e.what()) + ")");
			continue;
		}
		

		// Build the poly2tri inner contours for all holes we got from ClipperLib
		BOOST_FOREACH(ClipperLib::Polygon& opening, clip.holes) {
			
			contours.push_back(std::vector<p2t::Point*>());
			std::vector<p2t::Point*>& contour = contours.back();

			BOOST_FOREACH(ClipperLib::IntPoint& point, opening) {
				contour.push_back( new p2t::Point(from_int64(point.X), from_int64(point.Y)) );
			}

			cdt->AddHole(contour);
		}
		
		try {
			// Note: See above
			cdt->Triangulate();
		}
		catch(const std::exception& e) {
			IFCImporter::LogError("Ifc: error during polygon triangulation, skipping some openings: (poly2tri: " 
				+ std::string(e.what()) + ")");
			continue;
		}

		const std::vector<p2t::Triangle*>& tris = cdt->GetTriangles();

		// Collect the triangles we just produced
		BOOST_FOREACH(p2t::Triangle* tri, tris) {
			for(int i = 0; i < 3; ++i) {

				const IfcVector2& v = IfcVector2( 
					static_cast<IfcFloat>( tri->GetPoint(i)->x ), 
					static_cast<IfcFloat>( tri->GetPoint(i)->y )
				);

				assert(v.x <= 1.0 && v.x >= 0.0 && v.y <= 1.0 && v.y >= 0.0);
				const IfcVector3 v3 = minv * IfcVector3(vmin.x + v.x * vmax.x, vmin.y + v.y * vmax.y,coord) ; 

				curmesh.verts.push_back(v3);
			}
			curmesh.vertcnt.push_back(3);
		}

		result = true;
	}

	if (!result) {
		// revert -- it's a shame, but better than nothing
		curmesh.verts.insert(curmesh.verts.end(),old_verts.begin(), old_verts.end());
		curmesh.vertcnt.insert(curmesh.vertcnt.end(),old_vertcnt.begin(), old_vertcnt.end());

		IFCImporter::LogError("Ifc: revert, could not generate openings for this wall");
	}

	return result;
}


	} // ! IFC
} // ! Assimp

#undef to_int64
#undef from_int64
#undef one_vec

#endif