Adding upstream version 4:7.4.7.upstream/4%7.4.7upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 877 insertions, 0 deletions

diff --git a/basegfx/source/range/b2drangeclipper.cxx b/basegfx/source/range/b2drangeclipper.cxx
new file mode 100644
index 000000000..401ff20ca
--- /dev/null
+++ b/basegfx/source/range/b2drangeclipper.cxx
@@ -0,0 +1,877 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#include <osl/diagnose.h>
+
+#include <basegfx/range/b2drange.hxx>
+#include <basegfx/range/b2drangeclipper.hxx>
+#include <basegfx/polygon/b2dpolypolygon.hxx>
+#include <basegfx/range/b2drectangle.hxx>
+
+#include <o3tl/vector_pool.hxx>
+
+#include <algorithm>
+#include <cassert>
+#include <list>
+#include <iterator>
+
+namespace basegfx
+{
+    namespace
+    {
+        // Generating a poly-polygon from a bunch of rectangles
+
+        // Helper functionality for sweep-line algorithm
+        // ====================================================
+
+        class ImplPolygon;
+        typedef o3tl::vector_pool<ImplPolygon> VectorOfPolygons;
+
+        /** This class represents an active edge
+
+            As the sweep line traverses across the overall area,
+            rectangle edges parallel to it generate events, and
+            rectangle edges orthogonal to it generate active
+            edges. This class represents the latter.
+         */
+        class ActiveEdge
+        {
+        public:
+
+            enum EdgeDirection {
+                /// edge proceeds to the left
+                PROCEED_LEFT=0,
+                /// edge proceeds to the right
+                PROCEED_RIGHT=1
+            };
+
+            /** Create active edge
+
+                @param rRect
+                Rectangle this edge is part of
+
+                @param fInvariantCoord
+                The invariant coordinate value of this edge
+
+                @param eEdgeType
+                Is fInvariantCoord the lower or the higher value, for
+                this rect?
+             */
+            ActiveEdge( const B2DRectangle& rRect,
+                        const double&       fInvariantCoord,
+                        std::ptrdiff_t      nPolyIdx,
+                        EdgeDirection       eEdgeDirection ) :
+                mfInvariantCoord(fInvariantCoord),
+                mpAssociatedRect( &rRect ),
+                mnPolygonIdx( nPolyIdx ),
+                meEdgeDirection( eEdgeDirection )
+            {}
+
+            double              getInvariantCoord() const { return mfInvariantCoord; }
+            const B2DRectangle& getRect() const { return *mpAssociatedRect; }
+            std::ptrdiff_t      getTargetPolygonIndex() const { return mnPolygonIdx; }
+            void                setTargetPolygonIndex( std::ptrdiff_t nIdx ) { mnPolygonIdx = nIdx; }
+            EdgeDirection       getEdgeDirection() const { return meEdgeDirection; }
+
+        private:
+            /** The invariant coordinate value of this edge (e.g. the
+                common y value, for a horizontal edge)
+             */
+            double              mfInvariantCoord;
+
+            /** Associated rectangle
+
+                This on the one hand saves some storage space (the
+                vector of rectangles is persistent, anyway), and on
+                the other hand provides an identifier to match active
+                edges and x events (see below)
+
+                Ptr because class needs to be assignable
+             */
+            const B2DRectangle* mpAssociatedRect;
+
+            /** Index of the polygon this edge is currently involved
+                with.
+
+                Note that this can change for some kinds of edge
+                intersection, as the algorithm tends to swap
+                associated polygons there.
+
+                -1 denotes no assigned polygon
+             */
+            std::ptrdiff_t      mnPolygonIdx;
+
+            /// 'left' or 'right'
+            EdgeDirection       meEdgeDirection;
+        };
+
+        // Needs to be list - various places hold ptrs to elements
+        typedef std::list< ActiveEdge > ListOfEdges;
+
+        /** Element of the sweep line event list
+
+            As the sweep line traverses across the overall area,
+            rectangle edges parallel to it generate events, and
+            rectangle edges orthogonal to it generate active
+            edges. This class represents the former.
+
+            The class defines an element of the sweep line list. The
+            sweep line's position jumps in steps defined by the
+            coordinates of the sorted SweepLineEvent entries.
+         */
+        class SweepLineEvent
+        {
+        public:
+            /** The two possible sweep line rectangle edges differ by
+                one coordinate value - the starting edge has the
+                lower, the finishing edge the higher value.
+             */
+            enum EdgeType {
+                /// edge with lower coordinate value
+                STARTING_EDGE=0,
+                /// edge with higher coordinate value
+                FINISHING_EDGE=1
+            };
+
+            /** The two possible sweep line directions
+             */
+            enum EdgeDirection {
+                PROCEED_UP=0,
+                PROCEED_DOWN=1
+            };
+
+            /** Create sweep line event
+
+                @param fPos
+                Coordinate position of the event
+
+                @param rRect
+                Rectangle this event is generated for.
+
+                @param eEdgeType
+                Is fPos the lower or the higher value, for the
+                rectangle this event is generated for?
+             */
+            SweepLineEvent( double              fPos,
+                            const B2DRectangle& rRect,
+                            EdgeType            eEdgeType,
+                            EdgeDirection       eDirection) :
+                mfPos( fPos ),
+                mpAssociatedRect( &rRect ),
+                meEdgeType( eEdgeType ),
+                meEdgeDirection( eDirection )
+            {}
+
+            double              getPos() const { return mfPos; }
+            const B2DRectangle& getRect() const { return *mpAssociatedRect; }
+            EdgeType            getEdgeType() const { return meEdgeType; }
+            EdgeDirection       getEdgeDirection() const { return meEdgeDirection; }
+
+            /// For STL sort
+            bool operator<( const SweepLineEvent& rRHS ) const { return mfPos < rRHS.mfPos; }
+
+        private:
+            /// position of the event, in the direction of the line sweep
+            double                mfPos;
+
+            /** Rectangle this event is generated for
+
+                This on the one hand saves some storage space (the
+                vector of rectangles is persistent, anyway), and on
+                the other hand provides an identifier to match active
+                edges and events (see below)
+
+                Ptr because class needs to be assignable
+             */
+            const B2DRectangle*   mpAssociatedRect;
+
+            /// 'upper' or 'lower' edge of original rectangle.
+            EdgeType              meEdgeType;
+
+            /// 'up' or 'down'
+            EdgeDirection         meEdgeDirection;
+        };
+
+        typedef std::vector< SweepLineEvent > VectorOfEvents;
+
+        /** Smart point container for B2DMultiRange::getPolyPolygon()
+
+            This class provides methods needed only here, and is used
+            as a place to store some additional information per
+            polygon. Also, most of the intersection logic is
+            implemented here.
+         */
+        class ImplPolygon
+        {
+        public:
+            /** Create polygon
+             */
+            ImplPolygon() :
+                mpLeadingRightEdge(nullptr),
+                mnIdx(-1),
+                mbIsFinished(false)
+            {
+                // completely ad-hoc. but what the hell.
+                maPoints.reserve(11);
+            }
+
+            void setPolygonPoolIndex( std::ptrdiff_t nIdx ) { mnIdx = nIdx; }
+
+            /// Add point to the end of the existing points
+            void append( const B2DPoint& rPoint )
+            {
+                OSL_PRECOND( maPoints.empty() ||
+                             maPoints.back().getX() == rPoint.getX() ||
+                             maPoints.back().getY() == rPoint.getY(),
+                             "ImplPolygon::append(): added point violates 90 degree line angle constraint!" );
+
+                if( maPoints.empty() ||
+                    maPoints.back() != rPoint )
+                {
+                    // avoid duplicate points
+                    maPoints.push_back( rPoint );
+                }
+            }
+
+            /** Perform the intersection of this polygon with an
+                active edge.
+
+                @param rEvent
+                The vertical line event that generated the
+                intersection
+
+                @param rActiveEdge
+                The active edge that generated the intersection
+
+                @param rPolygonPool
+                Polygon pool, we sometimes need to allocate a new one
+
+                @param bIsFinishingEdge
+                True, when this is hitting the last edge of the
+                vertical sweep - every vertical sweep starts and ends
+                with upper and lower edge of the _same_ rectangle.
+
+                @return the new current polygon (that's the one
+                processing must proceed with, when going through the
+                list of upcoming active edges).
+             */
+            std::ptrdiff_t intersect( SweepLineEvent const & rEvent,
+                                      ActiveEdge&            rActiveEdge,
+                                      VectorOfPolygons&      rPolygonPool,
+                                      B2DPolyPolygon&        rRes,
+                                      bool                   isFinishingEdge )
+            {
+                OSL_PRECOND( !mbIsFinished,
+                             "ImplPolygon::intersect(): called on already finished polygon!" );
+                OSL_PRECOND( !isFinishingEdge || &rEvent.getRect() == &rActiveEdge.getRect(),
+                             "ImplPolygon::intersect(): inconsistent ending!" );
+
+                const B2DPoint aIntersectionPoint( rEvent.getPos(),
+                                                   rActiveEdge.getInvariantCoord() );
+
+                // intersection point, goes to our polygon
+                // unconditionally
+                append(aIntersectionPoint);
+
+                if( isFinishingEdge )
+                {
+                    // isSweepLineEnteringRect ?
+                    if( rEvent.getEdgeType() == SweepLineEvent::STARTING_EDGE)
+                        handleFinalOwnRightEdge(rActiveEdge);
+                    else
+                        handleFinalOwnLeftEdge(rActiveEdge,
+                                               rPolygonPool,
+                                               rRes);
+
+                    // we're done with this rect & sweep line
+                    return -1;
+                }
+                else if( metOwnEdge(rEvent,rActiveEdge) )
+                {
+                    handleInitialOwnEdge(rEvent, rActiveEdge);
+
+                    // point already added, all init done, continue
+                    // with same poly
+                    return mnIdx;
+                }
+                else
+                {
+                    OSL_ENSURE( rActiveEdge.getTargetPolygonIndex() != -1,
+                                "ImplPolygon::intersect(): non-trivial intersection hit empty polygon!" );
+
+                    const bool isHittingLeftEdge(
+                        rActiveEdge.getEdgeDirection() == ActiveEdge::PROCEED_LEFT);
+
+                    if( isHittingLeftEdge )
+                        return handleComplexLeftEdge(rActiveEdge,
+                                                     aIntersectionPoint,
+                                                     rPolygonPool,
+                                                     rRes);
+                    else
+                        return handleComplexRightEdge(rActiveEdge,
+                                                      aIntersectionPoint,
+                                                      rPolygonPool);
+                }
+            }
+
+        private:
+            void handleInitialOwnEdge(SweepLineEvent const & rEvent,
+                                      ActiveEdge const & rActiveEdge) const
+            {
+                const bool isActiveEdgeProceedLeft(
+                    rActiveEdge.getEdgeDirection() == ActiveEdge::PROCEED_LEFT);
+                const bool isSweepLineEnteringRect(
+                    rEvent.getEdgeType() == SweepLineEvent::STARTING_EDGE);
+
+                OSL_ENSURE( isSweepLineEnteringRect == isActiveEdgeProceedLeft,
+                            "ImplPolygon::intersect(): sweep initial own edge hit: wrong polygon order" );
+
+                OSL_ENSURE( isSweepLineEnteringRect ||
+                            mpLeadingRightEdge == &rActiveEdge,
+                            "ImplPolygon::intersect(): sweep initial own edge hit: wrong leading edge" );
+            }
+
+            void handleFinalOwnRightEdge(ActiveEdge& rActiveEdge)
+            {
+                OSL_ENSURE( rActiveEdge.getEdgeDirection() == ActiveEdge::PROCEED_RIGHT,
+                            "ImplPolygon::handleInitialOwnRightEdge(): start edge wrong polygon order" );
+
+                rActiveEdge.setTargetPolygonIndex(mnIdx);
+                mpLeadingRightEdge = &rActiveEdge;
+            }
+
+            void handleFinalOwnLeftEdge(ActiveEdge const & rActiveEdge,
+                                        VectorOfPolygons&  rPolygonPool,
+                                        B2DPolyPolygon&    rRes)
+            {
+                OSL_ENSURE( rActiveEdge.getEdgeDirection() == ActiveEdge::PROCEED_LEFT,
+                            "ImplPolygon::handleFinalOwnLeftEdge(): end edge wrong polygon order" );
+
+                const bool isHittingOurTail(
+                    rActiveEdge.getTargetPolygonIndex() == mnIdx);
+
+                if( isHittingOurTail )
+                    finish(rRes); // just finish. no fuss.
+                else
+                {
+                    // temp poly hits final left edge
+                    const std::ptrdiff_t nTmpIdx=rActiveEdge.getTargetPolygonIndex();
+                    ImplPolygon& rTmp=rPolygonPool.get(nTmpIdx);
+
+                    // active edge's polygon has points
+                    // already. ours need to go in front of them.
+                    maPoints.insert(maPoints.end(),
+                                    rTmp.maPoints.begin(),
+                                    rTmp.maPoints.end());
+
+                    // adjust leading edges, we're switching the polygon
+                    ActiveEdge* const pFarEdge=rTmp.mpLeadingRightEdge;
+
+                    mpLeadingRightEdge = pFarEdge;
+                    pFarEdge->setTargetPolygonIndex(mnIdx);
+
+                    // nTmpIdx is an empty shell, get rid of it
+                    rPolygonPool.free(nTmpIdx);
+                }
+            }
+
+            std::ptrdiff_t handleComplexLeftEdge(ActiveEdge&       rActiveEdge,
+                                                 const B2DPoint&   rIntersectionPoint,
+                                                 VectorOfPolygons& rPolygonPool,
+                                                 B2DPolyPolygon&   rRes)
+            {
+                const bool isHittingOurTail(
+                    rActiveEdge.getTargetPolygonIndex() == mnIdx);
+                if( isHittingOurTail )
+                {
+                    finish(rRes);
+
+                    // so "this" is done - need new polygon to collect
+                    // further points
+                    const std::ptrdiff_t nIdxNewPolygon=rPolygonPool.alloc();
+                    rPolygonPool.get(nIdxNewPolygon).setPolygonPoolIndex(nIdxNewPolygon);
+                    rPolygonPool.get(nIdxNewPolygon).append(rIntersectionPoint);
+
+                    rActiveEdge.setTargetPolygonIndex(nIdxNewPolygon);
+
+                    return nIdxNewPolygon;
+                }
+                else
+                {
+                    const std::ptrdiff_t nTmpIdx=rActiveEdge.getTargetPolygonIndex();
+                    ImplPolygon& rTmp=rPolygonPool.get(nTmpIdx);
+
+                    // active edge's polygon has points
+                    // already. ours need to go in front of them.
+                    maPoints.insert(maPoints.end(),
+                                    rTmp.maPoints.begin(),
+                                    rTmp.maPoints.end());
+
+                    rTmp.maPoints.clear();
+                    rTmp.append(rIntersectionPoint);
+
+                    // adjust leading edges, we're switching the polygon
+                    ActiveEdge* const pFarEdge=rTmp.mpLeadingRightEdge;
+                    ActiveEdge* const pNearEdge=&rActiveEdge;
+
+                    rTmp.mpLeadingRightEdge = nullptr;
+                    pNearEdge->setTargetPolygonIndex(nTmpIdx);
+
+                    mpLeadingRightEdge = pFarEdge;
+                    pFarEdge->setTargetPolygonIndex(mnIdx);
+
+                    return nTmpIdx;
+                }
+            }
+
+            std::ptrdiff_t handleComplexRightEdge(ActiveEdge&       rActiveEdge,
+                                                  const B2DPoint&   rIntersectionPoint,
+                                                  VectorOfPolygons& rPolygonPool)
+            {
+                const std::ptrdiff_t nTmpIdx=rActiveEdge.getTargetPolygonIndex();
+                ImplPolygon& rTmp=rPolygonPool.get(nTmpIdx);
+
+                rTmp.append(rIntersectionPoint);
+
+                rActiveEdge.setTargetPolygonIndex(mnIdx);
+                mpLeadingRightEdge = &rActiveEdge;
+
+                rTmp.mpLeadingRightEdge = nullptr;
+
+                return nTmpIdx;
+            }
+
+            /// True when sweep line hits our own active edge
+            static bool metOwnEdge(SweepLineEvent const & rEvent,
+                                   ActiveEdge const &     rActiveEdge)
+            {
+                const bool bHitOwnEdge=&rEvent.getRect() == &rActiveEdge.getRect();
+                return bHitOwnEdge;
+            }
+
+            /// Retrieve B2DPolygon from this object
+            B2DPolygon getPolygon() const
+            {
+                B2DPolygon aRes;
+                for (auto const& aPoint : maPoints)
+                    aRes.append(aPoint, 1);
+                aRes.setClosed( true );
+                return aRes;
+            }
+
+            /** Finish this polygon, push to result set.
+             */
+            void finish(B2DPolyPolygon& rRes)
+            {
+                OSL_PRECOND( maPoints.empty() ||
+                             maPoints.front().getX() == maPoints.back().getX() ||
+                             maPoints.front().getY() == maPoints.back().getY(),
+                             "ImplPolygon::finish(): first and last point violate 90 degree line angle constraint!" );
+
+                mbIsFinished = true;
+                mpLeadingRightEdge = nullptr;
+
+                rRes.append(getPolygon());
+            }
+
+            /** Refers to the current leading edge element of this
+                polygon, or NULL. The leading edge denotes the 'front'
+                of the polygon vertex sequence, i.e. the coordinates
+                at the polygon's leading edge are returned from
+                maPoints.front()
+             */
+            ActiveEdge*           mpLeadingRightEdge;
+
+            /// current index into vector pool
+            std::ptrdiff_t        mnIdx;
+
+            /// Container for the actual polygon points
+            std::vector<B2DPoint> maPoints;
+
+            /// When true, this polygon is 'done', i.e. nothing must be added anymore.
+            bool                  mbIsFinished;
+        };
+
+        /** Init sweep line event list
+
+            This method fills the event list with the sweep line
+            events generated from the input rectangles, and sorts them
+            with increasing x.
+         */
+        void setupSweepLineEventListFromRanges( VectorOfEvents& o_rEventVector,
+                                                const std::vector<B2DRange>& rRanges,
+                                                const std::vector<B2VectorOrientation>& rOrientations )
+        {
+            // we need exactly 2*rectVec.size() events: one for the
+            // left, and one for the right edge of each rectangle
+            o_rEventVector.clear();
+            o_rEventVector.reserve( 2*rRanges.size() );
+
+            // generate events
+            // ===============
+
+            // first pass: add all left edges in increasing order
+            std::vector<B2DRange>::const_iterator aCurrRect=rRanges.begin();
+            std::vector<B2VectorOrientation>::const_iterator aCurrOrientation=rOrientations.begin();
+            const std::vector<B2DRange>::const_iterator aEnd=rRanges.end();
+            const std::vector<B2VectorOrientation>::const_iterator aEndOrientation=rOrientations.end();
+            while( aCurrRect != aEnd && aCurrOrientation != aEndOrientation )
+            {
+                const B2DRectangle& rCurrRect( *aCurrRect++ );
+
+                o_rEventVector.emplace_back( rCurrRect.getMinX(),
+                                    rCurrRect,
+                                    SweepLineEvent::STARTING_EDGE,
+                                    (*aCurrOrientation++) == B2VectorOrientation::Positive ?
+                                    SweepLineEvent::PROCEED_UP : SweepLineEvent::PROCEED_DOWN );
+            }
+
+            // second pass: add all right edges in reversed order
+            std::vector<B2DRange>::const_reverse_iterator aCurrRectR=rRanges.rbegin();
+            std::vector<B2VectorOrientation>::const_reverse_iterator aCurrOrientationR=rOrientations.rbegin();
+            const std::vector<B2DRange>::const_reverse_iterator aEndR=rRanges.rend();
+            while( aCurrRectR != aEndR )
+            {
+                const B2DRectangle& rCurrRect( *aCurrRectR++ );
+
+                o_rEventVector.emplace_back( rCurrRect.getMaxX(),
+                                    rCurrRect,
+                                    SweepLineEvent::FINISHING_EDGE,
+                                    (*aCurrOrientationR++) == B2VectorOrientation::Positive ?
+                                    SweepLineEvent::PROCEED_DOWN : SweepLineEvent::PROCEED_UP );
+            }
+
+            // sort events
+            // ===========
+
+            // since we use stable_sort, the order of events with the
+            // same x value will not change. The elaborate two-pass
+            // add above thus ensures, that for each two rectangles
+            // with similar left and right x coordinates, the
+            // rectangle whose left event comes first will have its
+            // right event come last. This is advantageous for the
+            // clip algorithm below, see handleRightEdgeCrossing().
+
+            std::stable_sort( o_rEventVector.begin(),
+                              o_rEventVector.end() );
+        }
+
+        /** Insert two active edge segments for the given rectangle.
+
+            This method creates two active edge segments from the
+            given rect, and inserts them into the active edge list,
+            such that this stays sorted (if it was before).
+
+            @param io_rEdgeList
+            Active edge list to insert into
+
+            @param io_rPolygons
+            Vector of polygons. Each rectangle added creates one
+            tentative result polygon in this vector, and the edge list
+            entries holds a reference to that polygon (this _requires_
+            that the polygon vector does not reallocate, i.e. it must
+            have at least the maximal number of rectangles reserved)
+
+            @param o_CurrentPolygon
+            The then-current polygon when processing this sweep line
+            event
+
+            @param rCurrEvent
+            The actual event that caused this call
+         */
+        void createActiveEdgesFromStartEvent( ListOfEdges &          io_rEdgeList,
+                                              VectorOfPolygons &     io_rPolygonPool,
+                                              SweepLineEvent const & rCurrEvent )
+        {
+            ListOfEdges         aNewEdges;
+            const B2DRectangle& rRect=rCurrEvent.getRect();
+            const bool          bGoesDown=rCurrEvent.getEdgeDirection() == SweepLineEvent::PROCEED_DOWN;
+
+            // start event - new rect starts here, needs polygon to
+            // collect points into
+            const std::ptrdiff_t nIdxPolygon=io_rPolygonPool.alloc();
+            io_rPolygonPool.get(nIdxPolygon).setPolygonPoolIndex(nIdxPolygon);
+
+            // upper edge
+            aNewEdges.emplace_back(
+                    rRect,
+                    rRect.getMinY(),
+                    bGoesDown ? nIdxPolygon : -1,
+                    bGoesDown ? ActiveEdge::PROCEED_LEFT : ActiveEdge::PROCEED_RIGHT );
+            // lower edge
+            aNewEdges.emplace_back(
+                    rRect,
+                    rRect.getMaxY(),
+                    bGoesDown ? -1 : nIdxPolygon,
+                    bGoesDown ? ActiveEdge::PROCEED_RIGHT : ActiveEdge::PROCEED_LEFT );
+
+            // furthermore, have to respect a special tie-breaking
+            // rule here, for edges which share the same y value:
+            // newly added upper edges must be inserted _before_ any
+            // other edge with the same y value, and newly added lower
+            // edges must be _after_ all other edges with the same
+            // y. This ensures that the left vertical edge processing
+            // below encounters the upper edge of the current rect
+            // first, and the lower edge last, which automatically
+            // starts and finishes this rect correctly (as only then,
+            // the polygon will have their associated active edges
+            // set).
+            const double                nMinY( rRect.getMinY() );
+            const double                nMaxY( rRect.getMaxY() );
+            ListOfEdges::iterator       aCurr( io_rEdgeList.begin() );
+            const ListOfEdges::iterator aEnd ( io_rEdgeList.end() );
+            while( aCurr != aEnd )
+            {
+                const double nCurrY( aCurr->getInvariantCoord() );
+
+                if( nCurrY >= nMinY &&
+                    aNewEdges.size() == 2 ) // only add, if not yet done.
+                {
+                    // insert upper edge _before_ aCurr. Thus, it will
+                    // be the first entry for a range of equal y
+                    // values. Using splice here, since we hold
+                    // references to the moved list element!
+                    io_rEdgeList.splice( aCurr,
+                                         aNewEdges,
+                                         aNewEdges.begin() );
+                }
+
+                if( nCurrY > nMaxY )
+                {
+                    // insert lower edge _before_ aCurr. Thus, it will
+                    // be the last entry for a range of equal y values
+                    // (aCurr is the first entry strictly larger than
+                    // nMaxY). Using splice here, since we hold
+                    // references to the moved list element!
+                    io_rEdgeList.splice( aCurr,
+                                         aNewEdges,
+                                         aNewEdges.begin() );
+                    // done with insertion, can early-exit here.
+                    return;
+                }
+
+                ++aCurr;
+            }
+
+            // append remainder of aNewList (might still contain 2 or
+            // 1 elements, depending of the contents of io_rEdgeList).
+            io_rEdgeList.splice( aCurr,
+                                 aNewEdges );
+        }
+
+        bool isSameRect(ActiveEdge const &        rEdge,
+                               basegfx::B2DRange const & rRect)
+        {
+            return &rEdge.getRect() == &rRect;
+        }
+
+        // wow what a hack. necessary because stl's list::erase does
+        // not eat reverse_iterator
+        template<typename Cont, typename Iter> Iter eraseFromList(Cont&, const Iter&);
+        template<> ListOfEdges::iterator eraseFromList(
+            ListOfEdges& rList, const ListOfEdges::iterator& aIter)
+        {
+            return rList.erase(aIter);
+        }
+        template<> ListOfEdges::reverse_iterator eraseFromList(
+            ListOfEdges& rList, const ListOfEdges::reverse_iterator& aIter)
+        {
+            return ListOfEdges::reverse_iterator(
+                    rList.erase(std::prev(aIter.base())));
+        }
+
+        template<int bPerformErase,
+                 typename Iterator> void processActiveEdges(
+            Iterator          first,
+            Iterator          last,
+            ListOfEdges&      rActiveEdgeList,
+            SweepLineEvent const & rCurrEvent,
+            VectorOfPolygons& rPolygonPool,
+            B2DPolyPolygon&   rRes )
+        {
+            const basegfx::B2DRange& rCurrRect=rCurrEvent.getRect();
+
+            // fast-forward to rCurrEvent's first active edge (holds
+            // for both starting and finishing sweep line events, a
+            // rect is regarded _outside_ any rects whose events have
+            // started earlier
+            first = std::find_if(first, last,
+                                 [&rCurrRect](ActiveEdge& anEdge) { return isSameRect(anEdge, rCurrRect); });
+
+            if(first == last)
+                return;
+
+            int nCount=0;
+            std::ptrdiff_t nCurrPolyIdx=-1;
+            while(first != last)
+            {
+                if( nCurrPolyIdx == -1 )
+                    nCurrPolyIdx=first->getTargetPolygonIndex();
+
+                assert(nCurrPolyIdx != -1);
+
+                // second encounter of my rect -> second edge
+                // encountered, done
+                const bool bExit=
+                    nCount &&
+                    isSameRect(*first,
+                               rCurrRect);
+
+                // deal with current active edge
+                nCurrPolyIdx =
+                    rPolygonPool.get(nCurrPolyIdx).intersect(
+                        rCurrEvent,
+                        *first,
+                        rPolygonPool,
+                        rRes,
+                        bExit);
+
+                // prune upper & lower active edges, if requested
+                if( bPerformErase && (bExit || !nCount) )
+                    first = eraseFromList(rActiveEdgeList,first);
+                else
+                    ++first;
+
+                // delayed exit, had to prune first
+                if( bExit )
+                    return;
+
+                ++nCount;
+            }
+        }
+
+        template<int bPerformErase> void processActiveEdgesTopDown(
+            SweepLineEvent&   rCurrEvent,
+            ListOfEdges&      rActiveEdgeList,
+            VectorOfPolygons& rPolygonPool,
+            B2DPolyPolygon&   rRes )
+        {
+            processActiveEdges<bPerformErase>(
+                rActiveEdgeList. begin(),
+                rActiveEdgeList. end(),
+                rActiveEdgeList,
+                rCurrEvent,
+                rPolygonPool,
+                rRes);
+        }
+
+        template<int bPerformErase> void processActiveEdgesBottomUp(
+            SweepLineEvent&   rCurrEvent,
+            ListOfEdges&      rActiveEdgeList,
+            VectorOfPolygons& rPolygonPool,
+            B2DPolyPolygon&   rRes )
+        {
+            processActiveEdges<bPerformErase>(
+                rActiveEdgeList. rbegin(),
+                rActiveEdgeList. rend(),
+                rActiveEdgeList,
+                rCurrEvent,
+                rPolygonPool,
+                rRes);
+        }
+
+        enum{ NoErase=0, PerformErase=1 };
+
+        void handleStartingEdge( SweepLineEvent&   rCurrEvent,
+                                 ListOfEdges&      rActiveEdgeList,
+                                 VectorOfPolygons& rPolygonPool,
+                                 B2DPolyPolygon&   rRes)
+        {
+            // inject two new active edges for rect
+            createActiveEdgesFromStartEvent( rActiveEdgeList,
+                                             rPolygonPool,
+                                             rCurrEvent );
+
+            if( rCurrEvent.getEdgeDirection() == SweepLineEvent::PROCEED_DOWN )
+                processActiveEdgesTopDown<NoErase>(
+                    rCurrEvent, rActiveEdgeList, rPolygonPool, rRes);
+            else
+                processActiveEdgesBottomUp<NoErase>(
+                    rCurrEvent, rActiveEdgeList, rPolygonPool, rRes);
+        }
+
+        void handleFinishingEdge( SweepLineEvent&   rCurrEvent,
+                                  ListOfEdges&      rActiveEdgeList,
+                                  VectorOfPolygons& rPolygonPool,
+                                  B2DPolyPolygon&   rRes)
+        {
+            if( rCurrEvent.getEdgeDirection() == SweepLineEvent::PROCEED_DOWN )
+                processActiveEdgesTopDown<PerformErase>(
+                    rCurrEvent, rActiveEdgeList, rPolygonPool, rRes);
+            else
+                processActiveEdgesBottomUp<PerformErase>(
+                    rCurrEvent, rActiveEdgeList, rPolygonPool, rRes);
+        }
+
+        void handleSweepLineEvent( SweepLineEvent&   rCurrEvent,
+                                          ListOfEdges&      rActiveEdgeList,
+                                          VectorOfPolygons& rPolygonPool,
+                                          B2DPolyPolygon&   rRes)
+        {
+            if( rCurrEvent.getEdgeType() == SweepLineEvent::STARTING_EDGE )
+                handleStartingEdge(rCurrEvent,rActiveEdgeList,rPolygonPool,rRes);
+            else
+                handleFinishingEdge(rCurrEvent,rActiveEdgeList,rPolygonPool,rRes);
+        }
+    }
+
+    namespace utils
+    {
+        B2DPolyPolygon solveCrossovers(const std::vector<B2DRange>& rRanges,
+                                       const std::vector<B2VectorOrientation>& rOrientations)
+        {
+            // sweep-line algorithm to generate a poly-polygon
+            // from a bunch of rectangles
+            // ===============================================
+
+            // This algorithm uses the well-known sweep line
+            // concept, explained in every good text book about
+            // computational geometry.
+
+            // We start with creating two structures for every
+            // rectangle, one representing the left x coordinate,
+            // one representing the right x coordinate (and both
+            // referencing the original rect). These structs are
+            // sorted with increasing x coordinates.
+
+            // Then, we start processing the resulting list from
+            // the beginning. Every entry in the list defines a
+            // point in time of the line sweeping from left to
+            // right across all rectangles.
+            VectorOfEvents aSweepLineEvents;
+            setupSweepLineEventListFromRanges( aSweepLineEvents,
+                                               rRanges,
+                                               rOrientations );
+
+            B2DPolyPolygon   aRes;
+            VectorOfPolygons aPolygonPool;
+            ListOfEdges      aActiveEdgeList;
+
+            // sometimes not enough, but a usable compromise
+            aPolygonPool.reserve( rRanges.size() );
+
+            for (auto& aSweepLineEvent : aSweepLineEvents)
+                handleSweepLineEvent(aSweepLineEvent, aActiveEdgeList, aPolygonPool, aRes);
+
+            return aRes;
+        }
+    }
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */