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diff --git a/src/live_effects/lpe-knot.h b/src/live_effects/lpe-knot.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/** \file
+ * LPE knot effect implementation, see lpe-knot.cpp.
+ */
+/* Authors:
+ *   Jean-Francois Barraud <jf.barraud@gmail.com>
+ *   Johan Engelen <j.b.c.engelen@alumnus.utwente.nl>
+ *
+ * Copyright (C) Authors 2007-2012
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#ifndef INKSCAPE_LPE_KNOT_H
+#define INKSCAPE_LPE_KNOT_H
+
+
+#include "live_effects/effect.h"
+#include "live_effects/lpegroupbbox.h"
+#include "live_effects/parameter/array.h"
+#include "live_effects/parameter/hidden.h"
+#include "live_effects/parameter/parameter.h"
+//#include "live_effects/parameter/path.h"
+#include "live_effects/parameter/bool.h"
+#include "2geom/crossing.h"
+
+class SPLPEItem;
+
+namespace Inkscape {
+namespace LivePathEffect {
+
+class KnotHolderEntityCrossingSwitcher;
+
+// CrossingPoint, CrossingPoints:
+//   "point oriented" storage of crossing data (needed to find crossing nearest to a click, etc...)
+//TODO: evaluate how lpeknot-specific that is? Should something like this exist in 2geom?
+namespace LPEKnotNS {//just in case...
+struct CrossingPoint {
+  Geom::Point pt;
+  int sign; //+/-1 = positive or neg crossing, 0 = flat.
+  unsigned i, j;  //paths components meeting in this point.
+  unsigned ni, nj;  //this crossing is the ni-th along i, nj-th along j.
+  double ti, tj;  //time along paths.
+};
+
+class CrossingPoints : public  std::vector<CrossingPoint>{
+public:
+  CrossingPoints() : std::vector<CrossingPoint>() {}
+  CrossingPoints(Geom::CrossingSet const &cs, Geom::PathVector const &path);//for self crossings only!
+  CrossingPoints(Geom::PathVector const &paths);
+  CrossingPoints(std::vector<double> const &input);
+  std::vector<double> to_vector();
+  CrossingPoint get(unsigned const i, unsigned const ni);
+  void inherit_signs(CrossingPoints const &from_other, int default_value = 1);
+};
+} 
+
+class LPEKnot : public Effect, GroupBBoxEffect {
+public:
+  LPEKnot(LivePathEffectObject *lpeobject);
+  ~LPEKnot() override;
+  
+  void doBeforeEffect (SPLPEItem const* lpeitem) override;
+  Geom::PathVector doEffect_path (Geom::PathVector const & input_path) override;
+  
+  /* the knotholder entity classes must be declared friends */
+  friend class KnotHolderEntityCrossingSwitcher;
+  void addKnotHolderEntities(KnotHolder *knotholder, SPItem *item) override;
+
+protected:
+  void addCanvasIndicators(SPLPEItem const *lpeitem, std::vector<Geom::PathVector> &hp_vec) override;
+  Geom::PathVector supplied_path; //for knotholder business
+  
+private:
+  void updateSwitcher();
+ 
+  ScalarParam interruption_width;
+  BoolParam prop_to_stroke_width;
+  BoolParam both;
+  BoolParam inverse_width;
+  // "add_stroke_width" and "add_other_stroke_width" parameters are not used since Inkscape 1.0,
+  // but changed from bool to hidden parameter to retain backward compatibility and dont show in the UI
+  HiddenParam add_stroke_width;
+  HiddenParam add_other_stroke_width;
+  ScalarParam switcher_size;
+  ArrayParam<double> crossing_points_vector;//svg storage of crossing_points
+  
+  LPEKnotNS::CrossingPoints crossing_points;//topology representation of the knot.
+  
+  Geom::PathVector gpaths;//the collection of all the paths in the object or group.
+  std::vector<double> gstroke_widths;//the collection of all the stroke widths in the object or group.
+
+  //UI: please, someone, help me to improve this!!
+  unsigned selectedCrossing;//the selected crossing
+  Geom::Point switcher;//where to put the "switcher" helper
+  
+  LPEKnot(const LPEKnot&) = delete;
+  LPEKnot& operator=(const LPEKnot&) = delete;
+  
+};
+  
+} //namespace LivePathEffect
+} //namespace Inkscape
+
+#endif