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diff --git a/src/display/curve.cpp b/src/display/curve.cpp
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--- /dev/null
+++ b/src/display/curve.cpp
@@ -0,0 +1,713 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/**
+ * Authors:
+ * Lauris Kaplinski <lauris@kaplinski.com>
+ * Johan Engelen
+ *
+ * Copyright (C) 2000 Lauris Kaplinski
+ * Copyright (C) 2000-2001 Ximian, Inc.
+ * Copyright (C) 2002 Lauris Kaplinski
+ * Copyright (C) 2008 Johan Engelen
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include "display/curve.h"
+
+#include <glib.h>
+#include <2geom/pathvector.h>
+#include <2geom/sbasis-geometric.h>
+#include <2geom/sbasis-to-bezier.h>
+#include <2geom/point.h>
+
+#include <utility>
+
+/**
+ * Routines for SPCurve and for its Geom::PathVector
+ */
+
+/* Constructors */
+
+/**
+ * The returned curve's state is as if SPCurve::reset has just been called on it.
+ */
+SPCurve::SPCurve()
+ : _refcount(1),
+ _pathv()
+{}
+
+SPCurve::SPCurve(Geom::PathVector pathv)
+ : _refcount(1),
+ _pathv(std::move(pathv))
+{}
+
+//concat constructor
+SPCurve::SPCurve(std::list<SPCurve *> const& l) : _refcount(1)
+{
+ for (auto c:l) {
+ _pathv.insert( _pathv.end(), c->get_pathvector().begin(), c->get_pathvector().end() );
+ }
+}
+
+
+SPCurve *
+SPCurve::new_from_rect(Geom::Rect const &rect, bool all_four_sides)
+{
+ SPCurve *c = new SPCurve();
+
+ Geom::Point p = rect.corner(0);
+ c->moveto(p);
+
+ for (int i=3; i>=1; --i) {
+ c->lineto(rect.corner(i));
+ }
+
+ if (all_four_sides) {
+ // When _constrained_ snapping to a path, the 2geom::SimpleCrosser will be invoked which doesn't consider the closing segment.
+ // of a path. Consequently, in case we want to snap to for example the page border, we must provide all four sides of the
+ // rectangle explicitly
+ c->lineto(rect.corner(0));
+ } else {
+ // ... instead of just three plus a closing segment
+ c->closepath();
+ }
+
+ return c;
+}
+
+SPCurve::~SPCurve()
+= default;
+
+/* Methods */
+
+void
+SPCurve::set_pathvector(Geom::PathVector const & new_pathv)
+{
+ _pathv = new_pathv;
+}
+
+Geom::PathVector const &
+SPCurve::get_pathvector() const
+{
+ return _pathv;
+}
+
+/*
+ * Returns the number of segments of all paths summed
+ * This count includes the closing line segment of a closed path.
+ */
+size_t
+SPCurve::get_segment_count() const
+{
+ return _pathv.curveCount();
+}
+
+/**
+ * Increase _refcount of curve.
+ *
+ * \todo should this be shared with other refcounting code?
+ */
+SPCurve *
+SPCurve::ref()
+{
+ _refcount += 1;
+
+ return this;
+}
+
+/**
+ * Decrease refcount of curve, with possible destruction.
+ *
+ * \todo should this be shared with other refcounting code?
+ */
+SPCurve *
+SPCurve::unref()
+{
+ _refcount -= 1;
+
+ if (_refcount < 1) {
+ delete this;
+ }
+
+ return nullptr;
+}
+
+/**
+ * Create new curve from this curve's pathvector array.
+ */
+SPCurve *
+SPCurve::copy() const
+{
+ return new SPCurve(_pathv);
+}
+
+/**
+ * Return new curve that is the concatenation of all curves in list.
+ */
+SPCurve *
+SPCurve::concat(std::list<SPCurve *> l){
+ return new SPCurve(l);
+};
+
+/**
+ * Returns a list of new curves corresponding to the subpaths in \a curve.
+ * 2geomified
+ */
+std::list<SPCurve *>
+SPCurve::split() const
+{
+ std::list<SPCurve *> l;
+
+ for (const auto & path_it : _pathv) {
+ Geom::PathVector newpathv;
+ newpathv.push_back(path_it);
+ SPCurve * newcurve = new SPCurve(newpathv);
+ l.push_back(newcurve);
+ }
+
+ return l;
+}
+
+/**
+ * Transform all paths in curve using matrix.
+ */
+void
+SPCurve::transform(Geom::Affine const &m)
+{
+ _pathv *= m;
+}
+
+/**
+ * Set curve to empty curve.
+ * In more detail: this clears the internal pathvector from all its paths.
+ */
+void
+SPCurve::reset()
+{
+ _pathv.clear();
+}
+
+/** Several consecutive movetos are ALLOWED
+ * Ref: http://www.w3.org/TR/SVG11/implnote.html#PathElementImplementationNotes
+ * (first subitem of the item about zero-length path segments) */
+
+/**
+ * Calls SPCurve::moveto() with point made of given coordinates.
+ */
+void
+SPCurve::moveto(double x, double y)
+{
+ moveto(Geom::Point(x, y));
+}
+/**
+ * Perform a moveto to a point, thus starting a new subpath.
+ * Point p must be finite.
+ */
+void
+SPCurve::moveto(Geom::Point const &p)
+{
+ Geom::Path path(p);
+ path.setStitching(true);
+ _pathv.push_back(path);
+}
+
+/**
+ * Adds a line to the current subpath.
+ * Point p must be finite.
+ */
+void
+SPCurve::lineto(Geom::Point const &p)
+{
+ if (_pathv.empty()) g_message("SPCurve::lineto - path is empty!");
+ else _pathv.back().appendNew<Geom::LineSegment>( p );
+}
+/**
+ * Calls SPCurve::lineto( Geom::Point(x,y) )
+ */
+void
+SPCurve::lineto(double x, double y)
+{
+ lineto(Geom::Point(x,y));
+}
+
+/**
+ * Adds a quadratic bezier segment to the current subpath.
+ * All points must be finite.
+ */
+void
+SPCurve::quadto(Geom::Point const &p1, Geom::Point const &p2)
+{
+ if (_pathv.empty()) g_message("SPCurve::quadto - path is empty!");
+ else _pathv.back().appendNew<Geom::QuadraticBezier>( p1, p2);
+}
+/**
+ * Calls SPCurve::quadto( Geom::Point(x1,y1), Geom::Point(x2,y2) )
+ * All coordinates must be finite.
+ */
+void
+SPCurve::quadto(double x1, double y1, double x2, double y2)
+{
+ quadto( Geom::Point(x1,y1), Geom::Point(x2,y2) );
+}
+
+/**
+ * Adds a bezier segment to the current subpath.
+ * All points must be finite.
+ */
+void
+SPCurve::curveto(Geom::Point const &p0, Geom::Point const &p1, Geom::Point const &p2)
+{
+ if (_pathv.empty()) g_message("SPCurve::curveto - path is empty!");
+ else _pathv.back().appendNew<Geom::CubicBezier>( p0, p1, p2 );
+}
+/**
+ * Calls SPCurve::curveto( Geom::Point(x0,y0), Geom::Point(x1,y1), Geom::Point(x2,y2) )
+ * All coordinates must be finite.
+ */
+void
+SPCurve::curveto(double x0, double y0, double x1, double y1, double x2, double y2)
+{
+ curveto( Geom::Point(x0,y0), Geom::Point(x1,y1), Geom::Point(x2,y2) );
+}
+
+/**
+ * Close current subpath by possibly adding a line between start and end.
+ */
+void
+SPCurve::closepath()
+{
+ _pathv.back().close(true);
+}
+
+/** Like SPCurve::closepath() but sets the end point of the last subpath
+ to the subpath start point instead of adding a new lineto.
+
+ Used for freehand drawing when the user draws back to the start point.
+**/
+void
+SPCurve::closepath_current()
+{
+ if (_pathv.back().size() > 0 && dynamic_cast<Geom::LineSegment const *>(&_pathv.back().back_open())) {
+ _pathv.back().erase_last();
+ } else {
+ _pathv.back().setFinal(_pathv.back().initialPoint());
+ }
+ _pathv.back().close(true);
+}
+
+/**
+ * True if no paths are in curve. If it only contains a path with only a moveto, the path is considered NON-empty
+ */
+bool
+SPCurve::is_empty() const
+{
+ return _pathv.empty();
+}
+
+/**
+ * True if paths are in curve. If it only contains a path with only a moveto, the path is considered as unset FALSE
+ */
+bool
+SPCurve::is_unset() const
+{
+ if (get_segment_count()) {
+ return false;
+ }
+ return true;
+}
+
+/**
+ * True iff all subpaths are closed.
+ * Returns false if the curve is empty.
+ */
+bool
+SPCurve::is_closed() const
+{
+ if (is_empty()) {
+ return false;
+ }
+
+ for (const auto & it : _pathv) {
+ if ( ! it.closed() ) {
+ return false;
+ }
+ }
+
+ return true;
+}
+
+/**
+ * True if both curves are equal
+ */
+bool
+SPCurve::is_equal(SPCurve * other) const
+{
+ if(other == nullptr) {
+ return false;
+ }
+
+ if(_pathv == other->get_pathvector()){
+ return true;
+ }
+
+ return false;
+}
+
+/**
+ * Return last pathsegment (possibly the closing path segment) of the last path in PathVector or NULL.
+ * If the last path is empty (contains only a moveto), the function returns NULL
+ */
+Geom::Curve const *
+SPCurve::last_segment() const
+{
+ if (is_empty()) {
+ return nullptr;
+ }
+ if (_pathv.back().empty()) {
+ return nullptr;
+ }
+
+ return &_pathv.back().back_default();
+}
+
+/**
+ * Return last path in PathVector or NULL.
+ */
+Geom::Path const *
+SPCurve::last_path() const
+{
+ if (is_empty()) {
+ return nullptr;
+ }
+
+ return &_pathv.back();
+}
+
+/**
+ * Return first pathsegment in PathVector or NULL.
+ * equal in functionality to SPCurve::first_bpath()
+ */
+Geom::Curve const *
+SPCurve::first_segment() const
+{
+ if (is_empty()) {
+ return nullptr;
+ }
+ if (_pathv.front().empty()) {
+ return nullptr;
+ }
+
+ return &_pathv.front().front();
+}
+
+/**
+ * Return first path in PathVector or NULL.
+ */
+Geom::Path const *
+SPCurve::first_path() const
+{
+ if (is_empty()) {
+ return nullptr;
+ }
+
+ return &_pathv.front();
+}
+
+/**
+ * Return first point of first subpath or nothing when the path is empty.
+ */
+boost::optional<Geom::Point>
+SPCurve::first_point() const
+{
+ boost::optional<Geom::Point> retval;
+
+ if (!is_empty()) {
+ retval = _pathv.front().initialPoint();
+ }
+
+ return retval;
+}
+
+/**
+ * Return the second point of first subpath or _movePos if curve too short.
+ * If the pathvector is empty, this returns nothing. If the first path is only a moveto, this method
+ * returns the first point of the second path, if it exists. If there is no 2nd path, it returns the
+ * first point of the first path.
+ */
+boost::optional<Geom::Point>
+SPCurve::second_point() const
+{
+ boost::optional<Geom::Point> retval;
+ if (!is_empty()) {
+ if (_pathv.front().empty()) {
+ // first path is only a moveto
+ // check if there is second path
+ if (_pathv.size() > 1) {
+ retval = _pathv[1].initialPoint();
+ } else {
+ retval = _pathv[0].initialPoint();
+ }
+ } else {
+ retval = _pathv.front()[0].finalPoint();
+ }
+ }
+
+ return retval;
+}
+
+/**
+ * Return the second-last point of last subpath or first point when that last subpath has only a moveto.
+ */
+boost::optional<Geom::Point>
+SPCurve::penultimate_point() const
+{
+ boost::optional<Geom::Point> retval;
+ if (!is_empty()) {
+ Geom::Path const &lastpath = _pathv.back();
+ if (!lastpath.empty()) {
+ Geom::Curve const &back = lastpath.back_default();
+ retval = back.initialPoint();
+ } else {
+ retval = lastpath.initialPoint();
+ }
+ }
+
+ return retval;
+}
+
+/**
+ * Return last point of last subpath or nothing when the curve is empty.
+ * If the last path is only a moveto, then return that point.
+ */
+boost::optional<Geom::Point>
+SPCurve::last_point() const
+{
+ boost::optional<Geom::Point> retval;
+
+ if (!is_empty()) {
+ retval = _pathv.back().finalPoint();
+ }
+
+ return retval;
+}
+
+/**
+ * Returns a *new* \a curve but drawn in the opposite direction.
+ * Should result in the same shape, but
+ * with all its markers drawn facing the other direction.
+ * Reverses the order of subpaths as well
+ **/
+SPCurve *
+SPCurve::create_reverse() const
+{
+ SPCurve *new_curve = new SPCurve(_pathv.reversed());
+
+ return new_curve;
+}
+
+/**
+ * Append \a curve2 to \a this.
+ * If \a use_lineto is false, simply add all paths in \a curve2 to \a this;
+ * if \a use_lineto is true, combine \a this's last path and \a curve2's first path and add the rest of the paths in \a curve2 to \a this.
+ */
+void
+SPCurve::append(SPCurve const *curve2,
+ bool use_lineto)
+{
+ if (curve2->is_empty())
+ return;
+
+ if (use_lineto) {
+ Geom::PathVector::const_iterator it = curve2->_pathv.begin();
+ if ( ! _pathv.empty() ) {
+ Geom::Path & lastpath = _pathv.back();
+ lastpath.appendNew<Geom::LineSegment>( (*it).initialPoint() );
+ lastpath.append( (*it) );
+ } else {
+ _pathv.push_back( (*it) );
+ }
+
+ for (++it; it != curve2->_pathv.end(); ++it) {
+ _pathv.push_back( (*it) );
+ }
+ } else {
+ for (const auto & it : curve2->_pathv) {
+ _pathv.push_back( it );
+ }
+ }
+}
+
+/**
+ * Append \a c1 to \a this with possible fusing of close endpoints. If the end of this curve and the start of c1 are within tolerance distance,
+ * then the startpoint of c1 is moved to the end of this curve and the first subpath of c1 is appended to the last subpath of this curve.
+ * When one of the curves (this curve or the argument curve) is closed, the returned value is NULL; otherwise the returned value is this curve.
+ * When one of the curves is empty, this curves path becomes the non-empty path.
+ */
+SPCurve *
+SPCurve::append_continuous(SPCurve const *c1, double tolerance)
+{
+ using Geom::X;
+ using Geom::Y;
+
+ g_return_val_if_fail(c1 != nullptr, NULL);
+ if ( this->is_closed() || c1->is_closed() ) {
+ return nullptr;
+ }
+
+ if (c1->is_empty()) {
+ return this;
+ }
+
+ if (this->is_empty()) {
+ _pathv = c1->_pathv;
+ return this;
+ }
+
+ if ( (fabs((*this->last_point())[X] - (*c1->first_point())[X]) <= tolerance)
+ && (fabs((*this->last_point())[Y] - (*c1->first_point())[Y]) <= tolerance) )
+ {
+ // c1's first subpath can be appended to this curve's last subpath
+ Geom::PathVector::const_iterator path_it = c1->_pathv.begin();
+ Geom::Path & lastpath = _pathv.back();
+
+ Geom::Path newfirstpath(*path_it);
+ newfirstpath.setInitial(lastpath.finalPoint());
+ lastpath.append( newfirstpath );
+
+ for (++path_it; path_it != c1->_pathv.end(); ++path_it) {
+ _pathv.push_back( (*path_it) );
+ }
+
+ } else {
+ append(c1, true);
+ }
+
+ return this;
+}
+
+/**
+ * Remove last segment of curve.
+ * (Only used once in /src/pen-context.cpp)
+ */
+void
+SPCurve::backspace()
+{
+ if ( is_empty() )
+ return;
+
+ if ( !_pathv.back().empty() ) {
+ _pathv.back().erase_last();
+ _pathv.back().close(false);
+ }
+}
+
+/**
+ * TODO: add comments about what this method does and what assumptions are made and requirements are put on SPCurve
+ (2:08:18 AM) Johan: basically, i convert the path to pw<d2>
+(2:08:27 AM) Johan: then i calculate an offset path
+(2:08:29 AM) Johan: to move the knots
+(2:08:36 AM) Johan: then i add it
+(2:08:40 AM) Johan: then convert back to path
+If I remember correctly, this moves the firstpoint to new_p0, and the lastpoint to new_p1, and moves all nodes in between according to their arclength (interpolates the movement amount)
+ */
+void
+SPCurve::stretch_endpoints(Geom::Point const &new_p0, Geom::Point const &new_p1)
+{
+ if (is_empty()) {
+ return;
+ }
+
+ Geom::Point const offset0( new_p0 - *first_point() );
+ Geom::Point const offset1( new_p1 - *last_point() );
+
+ Geom::Piecewise<Geom::D2<Geom::SBasis> > pwd2 = _pathv.front().toPwSb();
+ Geom::Piecewise<Geom::SBasis> arclength = Geom::arcLengthSb(pwd2);
+ if ( arclength.lastValue() <= 0 ) {
+ g_error("SPCurve::stretch_endpoints - arclength <= 0");
+ throw;
+ }
+ arclength *= 1./arclength.lastValue();
+ Geom::Point const A( offset0 );
+ Geom::Point const B( offset1 );
+ Geom::Piecewise<Geom::SBasis> offsetx = (arclength*-1.+1)*A[0] + arclength*B[0];
+ Geom::Piecewise<Geom::SBasis> offsety = (arclength*-1.+1)*A[1] + arclength*B[1];
+ Geom::Piecewise<Geom::D2<Geom::SBasis> > offsetpath = Geom::sectionize( Geom::D2<Geom::Piecewise<Geom::SBasis> >(offsetx, offsety) );
+ pwd2 += offsetpath;
+ _pathv = Geom::path_from_piecewise( pwd2, 0.001 );
+}
+
+/**
+ * sets start of first path to new_p0, and end of first path to new_p1
+ */
+void
+SPCurve::move_endpoints(Geom::Point const &new_p0, Geom::Point const &new_p1)
+{
+ if (is_empty()) {
+ return;
+ }
+ _pathv.front().setInitial(new_p0);
+ _pathv.front().setFinal(new_p1);
+}
+
+/**
+ * returns the number of nodes in a path, used for statusbar text when selecting an spcurve.
+ * Sum of nodes in all the paths. When a path is closed, and its closing line segment is of zero-length,
+ * this function will not count the closing knot double (so basically ignores the closing line segment when it has zero length)
+ */
+size_t
+SPCurve::nodes_in_path() const
+{
+ size_t nr = 0;
+ for(const auto & it : _pathv) {
+ // if the path does not have any segments, it is a naked moveto,
+ // and therefore any path has at least one valid node
+ size_t psize = std::max<size_t>(1, it.size_closed());
+ nr += psize;
+ if (it.closed() && it.size_closed() > 0) {
+ const Geom::Curve &closingline = it.back_closed();
+ // the closing line segment is always of type
+ // Geom::LineSegment.
+ if (are_near(closingline.initialPoint(), closingline.finalPoint())) {
+ // closingline.isDegenerate() did not work, because it only checks for
+ // *exact* zero length, which goes wrong for relative coordinates and
+ // rounding errors...
+ // the closing line segment has zero-length. So stop before that one!
+ nr -= 1;
+ }
+ }
+ }
+
+ return nr;
+}
+
+/**
+ * Adds p to the last point (and last handle if present) of the last path
+ */
+void
+SPCurve::last_point_additive_move(Geom::Point const & p)
+{
+ if (is_empty()) {
+ return;
+ }
+
+ _pathv.back().setFinal( _pathv.back().finalPoint() + p );
+
+ // Move handle as well when the last segment is a cubic bezier segment:
+ // TODO: what to do for quadratic beziers?
+ if ( Geom::CubicBezier const *lastcube = dynamic_cast<Geom::CubicBezier const *>(&_pathv.back().back()) ) {
+ Geom::CubicBezier newcube( *lastcube );
+ newcube.setPoint(2, newcube[2] + p);
+ _pathv.back().replace( --_pathv.back().end(), newcube );
+ }
+}
+
+/*
+ Local Variables:
+ mode:c++
+ c-file-style:"stroustrup"
+ c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+ indent-tabs-mode:nil
+ fill-column:99
+ End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:
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