Adding upstream version 1.2.2.upstream/1.2.2upstream

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

1 files changed, 1356 insertions, 0 deletions

diff --git a/src/object/box3d.cpp b/src/object/box3d.cpp
new file mode 100644
index 0000000..49a57b8
--- /dev/null
+++ b/src/object/box3d.cpp
@@ -0,0 +1,1356 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * SVG <box3d> implementation
+ *
+ * Authors:
+ *   Maximilian Albert <Anhalter42@gmx.de>
+ *   Lauris Kaplinski <lauris@kaplinski.com>
+ *   bulia byak <buliabyak@users.sf.net>
+ *   Abhishek Sharma
+ *   Jon A. Cruz <jon@joncruz.org>
+ *
+ * Copyright (C) 2007      Authors
+ * Copyright (C) 1999-2002 Lauris Kaplinski
+ * Copyright (C) 2000-2001 Ximian, Inc.
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include "box3d.h"
+
+#include <glibmm/i18n.h>
+#include "attributes.h"
+#include "xml/document.h"
+#include "xml/repr.h"
+
+#include "bad-uri-exception.h"
+#include "box3d-side.h"
+#include "ui/tools/box3d-tool.h"
+#include "perspective-line.h"
+#include "persp3d-reference.h"
+#include "uri.h"
+#include <2geom/line.h>
+#include "sp-guide.h"
+#include "sp-namedview.h"
+
+#include "desktop.h"
+
+#include "include/macros.h"
+
+static void box3d_ref_changed(SPObject *old_ref, SPObject *ref, SPBox3D *box);
+
+static gint counter = 0;
+
+SPBox3D::SPBox3D() : SPGroup() {
+    this->my_counter = 0;
+    this->swapped = Box3D::NONE;
+
+    this->persp_href = nullptr;
+    this->persp_ref = new Persp3DReference(this);
+
+    /* we initialize the z-orders to zero so that they are updated during dragging */
+    for (int & z_order : z_orders) {
+        z_order = 0;
+    }
+}
+
+SPBox3D::~SPBox3D() = default;
+
+void SPBox3D::build(SPDocument *document, Inkscape::XML::Node *repr) {
+    SPGroup::build(document, repr);
+
+    my_counter = counter++;
+
+    /* we initialize the z-orders to zero so that they are updated during dragging */
+    for (int & z_order : z_orders) {
+        z_order = 0;
+    }
+
+    // TODO: Create/link to the correct perspective
+
+    if ( document ) {
+        persp_ref->changedSignal().connect(sigc::bind(sigc::ptr_fun(box3d_ref_changed), this));
+
+        readAttr(SPAttr::INKSCAPE_BOX3D_PERSPECTIVE_ID);
+        readAttr(SPAttr::INKSCAPE_BOX3D_CORNER0);
+        readAttr(SPAttr::INKSCAPE_BOX3D_CORNER7);
+    }
+}
+
+void SPBox3D::release() {
+    SPBox3D* object = this;
+    SPBox3D *box = object;
+
+    if (box->persp_href) {
+        g_free(box->persp_href);
+    }
+
+    // We have to store this here because the Persp3DReference gets destroyed below, but we need to
+    // access it to call Persp3D::remove_box(), which cannot be called earlier because the reference
+    // needs to be destroyed first.
+    Persp3D *persp = box->get_perspective();
+
+    if (box->persp_ref) {
+        box->persp_ref->detach();
+        delete box->persp_ref;
+        box->persp_ref = nullptr;
+    }
+    if (persp) {
+        persp->remove_box (box);
+
+        if (persp->perspective_impl->boxes.empty()) {
+            SPDocument *doc = box->document;
+            doc->setCurrentPersp3D(Persp3D::document_first_persp(doc));
+        }
+    }
+
+    SPGroup::release();
+}
+
+void SPBox3D::set(SPAttr key, const gchar* value) {
+    SPBox3D* object = this;
+    SPBox3D *box = object;
+
+    switch (key) {
+        case SPAttr::INKSCAPE_BOX3D_PERSPECTIVE_ID:
+            if ( value && box->persp_href && ( strcmp(value, box->persp_href) == 0 ) ) {
+                /* No change, do nothing. */
+            } else {
+                if (box->persp_href) {
+                    g_free(box->persp_href);
+                    box->persp_href = nullptr;
+                }
+                if (value) {
+                    box->persp_href = g_strdup(value);
+
+                    // Now do the attaching, which emits the changed signal.
+                    try {
+                        box->persp_ref->attach(Inkscape::URI(value));
+                    } catch (Inkscape::BadURIException &e) {
+                        g_warning("%s", e.what());
+                        box->persp_ref->detach();
+                    }
+                } else {
+                    // Detach, which emits the changed signal.
+                    box->persp_ref->detach();
+                }
+            }
+
+            // FIXME: Is the following update doubled by some call in either persp3d.cpp or vanishing_point_new.cpp?
+            box->position_set();
+            break;
+        case SPAttr::INKSCAPE_BOX3D_CORNER0:
+            if (value && strcmp(value, "0 : 0 : 0 : 0")) {
+                box->orig_corner0 = Proj::Pt3(value);
+                box->save_corner0 = box->orig_corner0;
+                box->position_set();
+            }
+            break;
+        case SPAttr::INKSCAPE_BOX3D_CORNER7:
+            if (value && strcmp(value, "0 : 0 : 0 : 0")) {
+                box->orig_corner7 = Proj::Pt3(value);
+                box->save_corner7 = box->orig_corner7;
+                box->position_set();
+            }
+            break;
+        default:
+            SPGroup::set(key, value);
+            break;
+    }
+}
+
+/**
+ * Gets called when (re)attached to another perspective.
+ */
+static void
+box3d_ref_changed(SPObject *old_ref, SPObject *ref, SPBox3D *box)
+{
+    if (old_ref && G_TYPE_CHECK_INSTANCE((gpointer)old_ref)) { // See issue 2390 (crash when quitting while dragging a 3D Box) ...
+        //... G_TYPE_CHECK_INSTANCE prevents triggering a glib assert after the SPObject has been deleted; a warning will still be thrown though
+        sp_signal_disconnect_by_data(old_ref, box);
+        Persp3D *oldPersp = dynamic_cast<Persp3D *>(old_ref);
+        if (oldPersp) {
+            oldPersp->remove_box(box);
+        }
+    }
+    Persp3D *persp = dynamic_cast<Persp3D *>(ref);
+    if ( persp && (ref != box) ) // FIXME: Comparisons sane?
+    {
+        persp->add_box(box);
+    }
+}
+
+void SPBox3D::update(SPCtx *ctx, guint flags) {
+    if (flags & (SP_OBJECT_MODIFIED_FLAG | SP_OBJECT_STYLE_MODIFIED_FLAG | SP_OBJECT_VIEWPORT_MODIFIED_FLAG)) {
+
+        /* FIXME?: Perhaps the display updates of box sides should be instantiated from here, but this
+           causes evil update loops so it's all done from SPBox3D::position_set, which is called from
+           various other places (like the handlers in shape-editor-knotholders.cpp, vanishing-point.cpp, etc. */
+
+    }
+
+    // Invoke parent method
+    SPGroup::update(ctx, flags);
+}
+
+Inkscape::XML::Node* SPBox3D::write(Inkscape::XML::Document *xml_doc, Inkscape::XML::Node *repr, guint flags) {
+    SPBox3D* object = this;
+    SPBox3D *box = object;
+
+    if ((flags & SP_OBJECT_WRITE_BUILD) && !repr) {
+        // this is where we end up when saving as plain SVG (also in other circumstances?)
+        // thus we don' set "sodipodi:type" so that the box is only saved as an ordinary svg:g
+        repr = xml_doc->createElement("svg:g");
+    }
+
+    if (flags & SP_OBJECT_WRITE_EXT) {
+
+        if (box->persp_href) {
+            repr->setAttribute("inkscape:perspectiveID", box->persp_href);
+        } else {
+            /* box is not yet linked to a perspective; use the document's current perspective */
+            SPDocument *doc = object->document;
+            if (box->persp_ref->getURI()) {
+                auto uri_string = box->persp_ref->getURI()->str();
+                repr->setAttributeOrRemoveIfEmpty("inkscape:perspectiveID", uri_string);
+            } else {
+                Glib::ustring href = "#";
+                href += doc->getCurrentPersp3D()->getId();
+                repr->setAttribute("inkscape:perspectiveID", href);
+            }
+        }
+
+        gchar *coordstr0 = box->orig_corner0.coord_string();
+        gchar *coordstr7 = box->orig_corner7.coord_string();
+        repr->setAttribute("inkscape:corner0", coordstr0);
+        repr->setAttribute("inkscape:corner7", coordstr7);
+        g_free(coordstr0);
+        g_free(coordstr7);
+
+        box->orig_corner0.normalize();
+        box->orig_corner7.normalize();
+
+        box->save_corner0 = box->orig_corner0;
+        box->save_corner7 = box->orig_corner7;
+    }
+
+    SPGroup::write(xml_doc, repr, flags);
+
+    return repr;
+}
+
+const char* SPBox3D::display_name() {
+    return _("3D Box");
+}
+
+void SPBox3D::position_set()
+{
+    /* This draws the curve and calls requestDisplayUpdate() for each side (the latter is done in
+       Box3DSide::position_set() to avoid update conflicts with the parent box) */
+    for (auto& obj: this->children) {
+        Box3DSide *side = dynamic_cast<Box3DSide *>(&obj);
+        if (side) {
+            side->position_set();
+        }
+    }
+}
+
+Geom::Affine SPBox3D::set_transform(Geom::Affine const &xform) {
+    // We don't apply the transform to the box directly but instead to its perspective (which is
+    // done in sp_selection_apply_affine). Here we only adjust strokes, patterns, etc.
+
+    Geom::Affine ret(Geom::Affine(xform).withoutTranslation());
+    gdouble const sw = hypot(ret[0], ret[1]);
+    gdouble const sh = hypot(ret[2], ret[3]);
+
+    for (auto& child: children) {
+        SPItem *childitem = dynamic_cast<SPItem *>(&child);
+        if (childitem) {
+            // Adjust stroke width
+            childitem->adjust_stroke(sqrt(fabs(sw * sh)));
+
+            // Adjust pattern fill
+            childitem->adjust_pattern(xform);
+
+            // Adjust gradient fill
+            childitem->adjust_gradient(xform);
+        }
+    }
+
+    return Geom::identity();
+}
+
+static Proj::Pt3
+box3d_get_proj_corner (guint id, Proj::Pt3 const &c0, Proj::Pt3 const &c7) {
+    return Proj::Pt3 ((id & Box3D::X) ? c7[Proj::X] : c0[Proj::X],
+                      (id & Box3D::Y) ? c7[Proj::Y] : c0[Proj::Y],
+                      (id & Box3D::Z) ? c7[Proj::Z] : c0[Proj::Z],
+                      1.0);
+}
+
+static Proj::Pt3
+box3d_get_proj_corner (SPBox3D const *box, guint id) {
+    return Proj::Pt3 ((id & Box3D::X) ? box->orig_corner7[Proj::X] : box->orig_corner0[Proj::X],
+                      (id & Box3D::Y) ? box->orig_corner7[Proj::Y] : box->orig_corner0[Proj::Y],
+                      (id & Box3D::Z) ? box->orig_corner7[Proj::Z] : box->orig_corner0[Proj::Z],
+                      1.0);
+}
+
+Geom::Point
+SPBox3D::get_corner_screen (guint id, bool item_coords) const {
+    Proj::Pt3 proj_corner (box3d_get_proj_corner (this, id));
+    if (!this->get_perspective()) {
+        return Geom::Point (Geom::infinity(), Geom::infinity());
+    }
+    Geom::Affine const i2d(this->i2dt_affine ());
+    if (item_coords) {
+        return this->get_perspective()->perspective_impl->tmat.image(proj_corner).affine() * i2d.inverse();
+    } else {
+        return this->get_perspective()->perspective_impl->tmat.image(proj_corner).affine();
+    }
+}
+
+Proj::Pt3
+SPBox3D::get_proj_center () {
+    this->orig_corner0.normalize();
+    this->orig_corner7.normalize();
+    return Proj::Pt3 ((this->orig_corner0[Proj::X] + this->orig_corner7[Proj::X]) / 2,
+                      (this->orig_corner0[Proj::Y] + this->orig_corner7[Proj::Y]) / 2,
+                      (this->orig_corner0[Proj::Z] + this->orig_corner7[Proj::Z]) / 2,
+                      1.0);
+}
+
+Geom::Point
+SPBox3D::get_center_screen () {
+    Proj::Pt3 proj_center (this->get_proj_center ());
+    if (!this->get_perspective()) {
+        return Geom::Point (Geom::infinity(), Geom::infinity());
+    }
+    Geom::Affine const i2d( this->i2dt_affine() );
+    return this->get_perspective()->perspective_impl->tmat.image(proj_center).affine() * i2d.inverse();
+}
+
+/*
+ * To keep the snappoint from jumping randomly between the two lines when the mouse pointer is close to
+ * their intersection, we remember the last snapped line and keep snapping to this specific line as long
+ * as the distance from the intersection to the mouse pointer is less than remember_snap_threshold.
+ */
+
+// Should we make the threshold settable in the preferences?
+static double remember_snap_threshold = 30;
+static guint remember_snap_index = 0;
+
+// constant for sizing the array of points to be considered:
+static const int MAX_POINT_COUNT = 4;
+
+static Proj::Pt3
+box3d_snap (SPBox3D *box, int id, Proj::Pt3 const &pt_proj, Proj::Pt3 const &start_pt) {
+    double z_coord = start_pt[Proj::Z];
+    double diff_x = box->save_corner7[Proj::X] - box->save_corner0[Proj::X];
+    double diff_y = box->save_corner7[Proj::Y] - box->save_corner0[Proj::Y];
+    double x_coord = start_pt[Proj::X];
+    double y_coord = start_pt[Proj::Y];
+    Proj::Pt3 A_proj (x_coord,          y_coord,          z_coord, 1.0);
+    Proj::Pt3 B_proj (x_coord + diff_x, y_coord,          z_coord, 1.0);
+    Proj::Pt3 C_proj (x_coord + diff_x, y_coord + diff_y, z_coord, 1.0);
+    Proj::Pt3 D_proj (x_coord,          y_coord + diff_y, z_coord, 1.0);
+    Proj::Pt3 E_proj (x_coord - diff_x, y_coord + diff_y, z_coord, 1.0);
+
+    Persp3DImpl *persp_impl = box->get_perspective()->perspective_impl;
+    Geom::Point A = persp_impl->tmat.image(A_proj).affine();
+    Geom::Point B = persp_impl->tmat.image(B_proj).affine();
+    Geom::Point C = persp_impl->tmat.image(C_proj).affine();
+    Geom::Point D = persp_impl->tmat.image(D_proj).affine();
+    Geom::Point E = persp_impl->tmat.image(E_proj).affine();
+    Geom::Point pt = persp_impl->tmat.image(pt_proj).affine();
+
+    // TODO: Replace these lines between corners with lines from a corner to a vanishing point
+    //       (this might help to prevent rounding errors if the box is small)
+    Box3D::Line pl1(A, B);
+    Box3D::Line pl2(A, D);
+    Box3D::Line diag1(A, (id == -1 || (!(id & Box3D::X) == !(id & Box3D::Y))) ? C : E);
+    Box3D::Line diag2(A, E); // diag2 is only taken into account if id equals -1, i.e., if we are snapping the center
+
+    int num_snap_lines = (id != -1) ? 3 : 4;
+    Geom::Point snap_pts[MAX_POINT_COUNT];
+
+    snap_pts[0] = pl1.closest_to (pt);
+    snap_pts[1] = pl2.closest_to (pt);
+    snap_pts[2] = diag1.closest_to (pt);
+    if (id == -1) {
+        snap_pts[3] = diag2.closest_to (pt);
+    }
+
+    gdouble const zoom = SP_ACTIVE_DESKTOP->current_zoom();
+
+    // determine the distances to all potential snapping points
+    double snap_dists[MAX_POINT_COUNT];
+    for (int i = 0; i < num_snap_lines; ++i) {
+        snap_dists[i] = Geom::L2 (snap_pts[i] - pt) * zoom;
+    }
+
+    // while we are within a given tolerance of the starting point,
+    // keep snapping to the same point to avoid jumping
+    bool within_tolerance = true;
+    for (int i = 0; i < num_snap_lines; ++i) {
+        if (snap_dists[i] > remember_snap_threshold) {
+            within_tolerance = false;
+            break;
+        }
+    }
+
+    // find the closest snapping point
+    int snap_index = -1;
+    double snap_dist = Geom::infinity();
+    for (int i = 0; i < num_snap_lines; ++i) {
+        if (snap_dists[i] < snap_dist) {
+            snap_index = i;
+            snap_dist = snap_dists[i];
+        }
+    }
+
+    // snap to the closest point (or the previously remembered one
+    // if we are within tolerance of the starting point)
+    Geom::Point result;
+    if (within_tolerance) {
+        result = snap_pts[remember_snap_index];
+    } else {
+        remember_snap_index = snap_index;
+        result = snap_pts[snap_index];
+    }
+    return box->get_perspective()->perspective_impl->tmat.preimage (result, z_coord, Proj::Z);
+}
+
+SPBox3D * SPBox3D::createBox3D(SPItem * parent)
+{
+    SPBox3D *box3d = nullptr;
+    Inkscape::XML::Document *xml_doc = parent->document->getReprDoc();
+    Inkscape::XML::Node *repr = xml_doc->createElement("svg:g");
+    repr->setAttribute("sodipodi:type", "inkscape:box3d");
+    box3d = reinterpret_cast<SPBox3D *>(parent->appendChildRepr(repr));
+    return box3d;
+}
+
+void
+SPBox3D::set_corner (const guint id, Geom::Point const &new_pos, const Box3D::Axis movement, bool constrained) {
+    g_return_if_fail ((movement != Box3D::NONE) && (movement != Box3D::XYZ));
+
+    this->orig_corner0.normalize();
+    this->orig_corner7.normalize();
+
+    /* update corners 0 and 7 according to which handle was moved and to the axes of movement */
+    if (!(movement & Box3D::Z)) {
+        Persp3DImpl *persp_impl = this->get_perspective()->perspective_impl;
+        Proj::Pt3 pt_proj (persp_impl->tmat.preimage (new_pos, (id < 4) ? this->orig_corner0[Proj::Z] :
+                                                      this->orig_corner7[Proj::Z], Proj::Z));
+        if (constrained) {
+            pt_proj = box3d_snap (this, id, pt_proj, box3d_get_proj_corner (id, this->save_corner0, this->save_corner7));
+        }
+
+        // normalizing pt_proj is essential because we want to mingle affine coordinates
+        pt_proj.normalize();
+        this->orig_corner0 = Proj::Pt3 ((id & Box3D::X) ? this->save_corner0[Proj::X] : pt_proj[Proj::X],
+                                       (id & Box3D::Y) ? this->save_corner0[Proj::Y] : pt_proj[Proj::Y],
+                                       this->save_corner0[Proj::Z],
+                                       1.0);
+        this->orig_corner7 = Proj::Pt3 ((id & Box3D::X) ? pt_proj[Proj::X] : this->save_corner7[Proj::X],
+                                       (id & Box3D::Y) ? pt_proj[Proj::Y] : this->save_corner7[Proj::Y],
+                                       this->save_corner7[Proj::Z],
+                                       1.0);
+    } else {
+        Persp3D *persp = this->get_perspective();
+        Persp3DImpl *persp_impl = this->get_perspective()->perspective_impl;
+        Box3D::PerspectiveLine pl(persp_impl->tmat.image(
+                                      box3d_get_proj_corner (id, this->save_corner0, this->save_corner7)).affine(),
+                                  Proj::Z, persp);
+        Geom::Point new_pos_snapped(pl.closest_to(new_pos));
+        Proj::Pt3 pt_proj (persp_impl->tmat.preimage (new_pos_snapped,
+                                      box3d_get_proj_corner (this, id)[(movement & Box3D::Y) ? Proj::X : Proj::Y],
+                                                      (movement & Box3D::Y) ? Proj::X : Proj::Y));
+        bool corner0_move_x = !(id & Box3D::X) && (movement & Box3D::X);
+        bool corner0_move_y = !(id & Box3D::Y) && (movement & Box3D::Y);
+        bool corner7_move_x =  (id & Box3D::X) && (movement & Box3D::X);
+        bool corner7_move_y =  (id & Box3D::Y) && (movement & Box3D::Y);
+        // normalizing pt_proj is essential because we want to mingle affine coordinates
+        pt_proj.normalize();
+        this->orig_corner0 = Proj::Pt3 (corner0_move_x ? pt_proj[Proj::X] : this->orig_corner0[Proj::X],
+                                       corner0_move_y ? pt_proj[Proj::Y] : this->orig_corner0[Proj::Y],
+                                       (id & Box3D::Z) ? this->orig_corner0[Proj::Z] : pt_proj[Proj::Z],
+                                       1.0);
+        this->orig_corner7 = Proj::Pt3 (corner7_move_x ? pt_proj[Proj::X] : this->orig_corner7[Proj::X],
+                                       corner7_move_y ? pt_proj[Proj::Y] : this->orig_corner7[Proj::Y],
+                                       (id & Box3D::Z) ? pt_proj[Proj::Z] : this->orig_corner7[Proj::Z],
+                                       1.0);
+    }
+    // FIXME: Should we update the box here? If so, how?
+}
+
+void SPBox3D::set_center (Geom::Point const &new_pos, Geom::Point const &old_pos, const Box3D::Axis movement, bool constrained) {
+    g_return_if_fail ((movement != Box3D::NONE) && (movement != Box3D::XYZ));
+
+    this->orig_corner0.normalize();
+    this->orig_corner7.normalize();
+
+    Persp3D *persp = this->get_perspective();
+    if (!(movement & Box3D::Z)) {
+        double coord = (this->orig_corner0[Proj::Z] + this->orig_corner7[Proj::Z]) / 2;
+        double radx = (this->orig_corner7[Proj::X] - this->orig_corner0[Proj::X]) / 2;
+        double rady = (this->orig_corner7[Proj::Y] - this->orig_corner0[Proj::Y]) / 2;
+
+        Proj::Pt3 pt_proj (persp->perspective_impl->tmat.preimage (new_pos, coord, Proj::Z));
+        if (constrained) {
+            Proj::Pt3 old_pos_proj (persp->perspective_impl->tmat.preimage (old_pos, coord, Proj::Z));
+            old_pos_proj.normalize();
+            pt_proj = box3d_snap (this, -1, pt_proj, old_pos_proj);
+        }
+        // normalizing pt_proj is essential because we want to mingle affine coordinates
+        pt_proj.normalize();
+        this->orig_corner0 = Proj::Pt3 ((movement & Box3D::X) ? pt_proj[Proj::X] - radx : this->orig_corner0[Proj::X],
+                                       (movement & Box3D::Y) ? pt_proj[Proj::Y] - rady : this->orig_corner0[Proj::Y],
+                                       this->orig_corner0[Proj::Z],
+                                       1.0);
+        this->orig_corner7 = Proj::Pt3 ((movement & Box3D::X) ? pt_proj[Proj::X] + radx : this->orig_corner7[Proj::X],
+                                       (movement & Box3D::Y) ? pt_proj[Proj::Y] + rady : this->orig_corner7[Proj::Y],
+                                       this->orig_corner7[Proj::Z],
+                                       1.0);
+    } else {
+        double coord = (this->orig_corner0[Proj::X] + this->orig_corner7[Proj::X]) / 2;
+        double radz = (this->orig_corner7[Proj::Z] - this->orig_corner0[Proj::Z]) / 2;
+
+        Box3D::PerspectiveLine pl(old_pos, Proj::Z, persp);
+        Geom::Point new_pos_snapped(pl.closest_to(new_pos));
+        Proj::Pt3 pt_proj (persp->perspective_impl->tmat.preimage (new_pos_snapped, coord, Proj::X));
+
+        /* normalizing pt_proj is essential because we want to mingle affine coordinates */
+        pt_proj.normalize();
+        this->orig_corner0 = Proj::Pt3 (this->orig_corner0[Proj::X],
+                                       this->orig_corner0[Proj::Y],
+                                       pt_proj[Proj::Z] - radz,
+                                       1.0);
+        this->orig_corner7 = Proj::Pt3 (this->orig_corner7[Proj::X],
+                                       this->orig_corner7[Proj::Y],
+                                       pt_proj[Proj::Z] + radz,
+                                       1.0);
+    }
+}
+
+/*
+ * Manipulates corner1 through corner4 to contain the indices of the corners
+ * from which the perspective lines in the direction of 'axis' emerge
+ */
+void SPBox3D::corners_for_PLs (Proj::Axis axis,
+                            Geom::Point &corner1, Geom::Point &corner2, Geom::Point &corner3, Geom::Point &corner4) const
+{
+    Persp3D *persp = this->get_perspective();
+    g_return_if_fail (persp);
+    Persp3DImpl *persp_impl = persp->perspective_impl;
+    //this->orig_corner0.normalize();
+    //this->orig_corner7.normalize();
+    double coord = (this->orig_corner0[axis] > this->orig_corner7[axis]) ?
+        this->orig_corner0[axis] :
+        this->orig_corner7[axis];
+
+    Proj::Pt3 c1, c2, c3, c4;
+    // FIXME: This can certainly be done more elegantly/efficiently than by a case-by-case analysis.
+    switch (axis) {
+        case Proj::X:
+            c1 = Proj::Pt3 (coord, this->orig_corner0[Proj::Y], this->orig_corner0[Proj::Z], 1.0);
+            c2 = Proj::Pt3 (coord, this->orig_corner7[Proj::Y], this->orig_corner0[Proj::Z], 1.0);
+            c3 = Proj::Pt3 (coord, this->orig_corner7[Proj::Y], this->orig_corner7[Proj::Z], 1.0);
+            c4 = Proj::Pt3 (coord, this->orig_corner0[Proj::Y], this->orig_corner7[Proj::Z], 1.0);
+            break;
+        case Proj::Y:
+            c1 = Proj::Pt3 (this->orig_corner0[Proj::X], coord, this->orig_corner0[Proj::Z], 1.0);
+            c2 = Proj::Pt3 (this->orig_corner7[Proj::X], coord, this->orig_corner0[Proj::Z], 1.0);
+            c3 = Proj::Pt3 (this->orig_corner7[Proj::X], coord, this->orig_corner7[Proj::Z], 1.0);
+            c4 = Proj::Pt3 (this->orig_corner0[Proj::X], coord, this->orig_corner7[Proj::Z], 1.0);
+            break;
+        case Proj::Z:
+            c1 = Proj::Pt3 (this->orig_corner7[Proj::X], this->orig_corner7[Proj::Y], coord, 1.0);
+            c2 = Proj::Pt3 (this->orig_corner7[Proj::X], this->orig_corner0[Proj::Y], coord, 1.0);
+            c3 = Proj::Pt3 (this->orig_corner0[Proj::X], this->orig_corner0[Proj::Y], coord, 1.0);
+            c4 = Proj::Pt3 (this->orig_corner0[Proj::X], this->orig_corner7[Proj::Y], coord, 1.0);
+            break;
+        default:
+            return;
+    }
+    corner1 = persp_impl->tmat.image(c1).affine();
+    corner2 = persp_impl->tmat.image(c2).affine();
+    corner3 = persp_impl->tmat.image(c3).affine();
+    corner4 = persp_impl->tmat.image(c4).affine();
+}
+
+/* Auxiliary function: Checks whether the half-line from A to B crosses the line segment joining C and D */
+static bool
+box3d_half_line_crosses_joining_line (Geom::Point const &A, Geom::Point const &B,
+                                      Geom::Point const &C, Geom::Point const &D) {
+    Geom::Point n0 = (B - A).ccw();
+    double d0 = dot(n0,A);
+
+    Geom::Point n1 = (D - C).ccw();
+    double d1 = dot(n1,C);
+
+    Geom::Line lineAB(A,B);
+    Geom::Line lineCD(C,D);
+
+    Geom::OptCrossing inters = Geom::OptCrossing(); // empty by default
+    try
+    {
+        inters = Geom::intersection(lineAB, lineCD);
+    }
+    catch (Geom::InfiniteSolutions& e)
+    {
+        // We're probably dealing with parallel lines, so they don't really cross
+        return false;
+    }
+
+    if (!inters) {
+        return false;
+    }
+
+    Geom::Point E = lineAB.pointAt((*inters).ta); // the point of intersection
+
+    if ((dot(C,n0) < d0) == (dot(D,n0) < d0)) {
+        // C and D lie on the same side of the line AB
+        return false;
+    }
+    if ((dot(A,n1) < d1) != (dot(B,n1) < d1)) {
+        // A and B lie on different sides of the line CD
+        return true;
+    } else if (Geom::distance(E,A) < Geom::distance(E,B)) {
+        // The line CD passes on the "wrong" side of A
+        return false;
+    }
+
+    // The line CD passes on the "correct" side of A
+    return true;
+}
+
+static bool
+box3d_XY_axes_are_swapped (SPBox3D *box) {
+    Persp3D *persp = box->get_perspective();
+    g_return_val_if_fail(persp, false);
+    Box3D::PerspectiveLine l1(box->get_corner_screen(3, false), Proj::X, persp);
+    Box3D::PerspectiveLine l2(box->get_corner_screen(3, false), Proj::Y, persp);
+    Geom::Point v1(l1.direction());
+    Geom::Point v2(l2.direction());
+    v1.normalize();
+    v2.normalize();
+
+    return (v1[Geom::X]*v2[Geom::Y] - v1[Geom::Y]*v2[Geom::X] > 0);
+}
+
+static inline void
+box3d_aux_set_z_orders (int z_orders[6], int a, int b, int c, int d, int e, int f) {
+    // TODO add function argument: SPDocument *doc = box->document
+    auto doc = SP_ACTIVE_DOCUMENT;
+
+    if (doc->is_yaxisdown()) {
+        std::swap(a, f);
+        std::swap(b, e);
+        std::swap(c, d);
+    }
+
+    z_orders[0] = a;
+    z_orders[1] = b;
+    z_orders[2] = c;
+    z_orders[3] = d;
+    z_orders[4] = e;
+    z_orders[5] = f;
+}
+
+
+/*
+ * In standard perspective we have:
+ * 2 = front face
+ * 1 = top face
+ * 0 = left face
+ * 3 = right face
+ * 4 = bottom face
+ * 5 = rear face
+ */
+
+/* All VPs infinite */
+static void
+box3d_set_new_z_orders_case0 (SPBox3D *box, int z_orders[6], Box3D::Axis central_axis) {
+    bool swapped = box3d_XY_axes_are_swapped(box);
+
+    switch(central_axis) {
+        case Box3D::X:
+            if (!swapped) {
+                box3d_aux_set_z_orders (z_orders, 2, 0, 4, 1, 3, 5);
+            } else {
+                box3d_aux_set_z_orders (z_orders, 3, 1, 5, 2, 4, 0);
+            }
+            break;
+        case Box3D::Y:
+            if (!swapped) {
+                box3d_aux_set_z_orders (z_orders, 2, 3, 1, 4, 0, 5);
+            } else {
+                box3d_aux_set_z_orders (z_orders, 5, 0, 4, 1, 3, 2);
+            }
+            break;
+        case Box3D::Z:
+            if (!swapped) {
+                box3d_aux_set_z_orders (z_orders, 2, 0, 1, 4, 3, 5);
+            } else {
+                box3d_aux_set_z_orders (z_orders, 5, 3, 4, 1, 0, 2);
+            }
+            break;
+        case Box3D::NONE:
+            if (!swapped) {
+                box3d_aux_set_z_orders (z_orders, 2, 3, 4, 1, 0, 5);
+            } else {
+                box3d_aux_set_z_orders (z_orders, 5, 0, 1, 4, 3, 2);
+            }
+            break;
+        default:
+            g_assert_not_reached();
+            break;
+    }
+}
+
+/* Precisely one finite VP */
+static void
+box3d_set_new_z_orders_case1 (SPBox3D *box, int z_orders[6], Box3D::Axis central_axis, Box3D::Axis fin_axis) {
+    Persp3D *persp = box->get_perspective();
+    Geom::Point vp(persp->get_VP(Box3D::toProj(fin_axis)).affine());
+
+    // note: in some of the case distinctions below we rely upon the fact that oaxis1 and oaxis2 are ordered
+    Box3D::Axis oaxis1 = Box3D::get_remaining_axes(fin_axis).first;
+    Box3D::Axis oaxis2 = Box3D::get_remaining_axes(fin_axis).second;
+    int inside1 = 0;
+    int inside2 = 0;
+    inside1 = box->pt_lies_in_PL_sector (vp, 3, 3 ^ oaxis2, oaxis1);
+    inside2 = box->pt_lies_in_PL_sector (vp, 3, 3 ^ oaxis1, oaxis2);
+
+    bool swapped = box3d_XY_axes_are_swapped(box);
+
+    switch(central_axis) {
+        case Box3D::X:
+            if (!swapped) {
+                box3d_aux_set_z_orders (z_orders, 2, 4, 0, 1, 3, 5);
+            } else {
+                box3d_aux_set_z_orders (z_orders, 5, 3, 1, 0, 2, 4);
+            }
+            break;
+        case Box3D::Y:
+            if (inside2 > 0) {
+                box3d_aux_set_z_orders (z_orders, 1, 2, 3, 0, 5, 4);
+            } else if (inside2 < 0) {
+                box3d_aux_set_z_orders (z_orders, 2, 3, 1, 4, 0, 5);
+            } else {
+                if (!swapped) {
+                    box3d_aux_set_z_orders (z_orders, 2, 3, 1, 5, 0, 4);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 5, 0, 4, 1, 3, 2);
+                }
+            }
+            break;
+        case Box3D::Z:
+            if (inside2) {
+                if (!swapped) {
+                    box3d_aux_set_z_orders (z_orders, 2, 1, 3, 0, 4, 5);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 5, 3, 4, 0, 1, 2);
+                }
+            } else if (inside1) {
+                if (!swapped) {
+                    box3d_aux_set_z_orders (z_orders, 2, 0, 1, 4, 3, 5);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 5, 3, 4, 1, 0, 2);
+                }
+            } else {
+                // "regular" case
+                if (!swapped) {
+                    box3d_aux_set_z_orders (z_orders, 0, 1, 2, 5, 4, 3);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 5, 3, 4, 0, 2, 1);
+                }
+            }
+            break;
+        case Box3D::NONE:
+            if (!swapped) {
+                box3d_aux_set_z_orders (z_orders, 2, 3, 4, 5, 0, 1);
+            } else {
+                box3d_aux_set_z_orders (z_orders, 5, 0, 1, 3, 2, 4);
+            }
+            break;
+        default:
+            g_assert_not_reached();
+    }
+}
+
+/* Precisely 2 finite VPs */
+static void
+box3d_set_new_z_orders_case2 (SPBox3D *box, int z_orders[6], Box3D::Axis central_axis, Box3D::Axis /*infinite_axis*/) {
+    bool swapped = box3d_XY_axes_are_swapped(box);
+
+    int insidexy = box->VP_lies_in_PL_sector (Proj::X, 3, 3 ^ Box3D::Z, Box3D::Y);
+    //int insidexz = box->VP_lies_in_PL_sector (Proj::X, 3, 3 ^ Box3D::Y, Box3D::Z);
+
+    int insideyx = box->VP_lies_in_PL_sector (Proj::Y, 3, 3 ^ Box3D::Z, Box3D::X);
+    int insideyz = box->VP_lies_in_PL_sector (Proj::Y, 3, 3 ^ Box3D::X, Box3D::Z);
+
+    //int insidezx = box->VP_lies_in_PL_sector (Proj::Z, 3, 3 ^ Box3D::Y, Box3D::X);
+    int insidezy = box->VP_lies_in_PL_sector (Proj::Z, 3, 3 ^ Box3D::X, Box3D::Y);
+
+    switch(central_axis) {
+        case Box3D::X:
+            if (!swapped) {
+                if (insidezy == -1) {
+                    box3d_aux_set_z_orders (z_orders, 2, 4, 0, 1, 3, 5);
+                } else if (insidexy == 1) {
+                    box3d_aux_set_z_orders (z_orders, 2, 4, 0, 5, 1, 3);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 2, 4, 0, 1, 3, 5);
+                }
+            } else {
+                if (insideyz == -1) {
+                    box3d_aux_set_z_orders (z_orders, 3, 1, 5, 0, 2, 4);
+                } else {
+                    if (!swapped) {
+                        box3d_aux_set_z_orders (z_orders, 3, 1, 5, 2, 4, 0);
+                    } else {
+                        if (insidexy == 0) {
+                            box3d_aux_set_z_orders (z_orders, 3, 5, 1, 0, 2, 4);
+                        } else {
+                            box3d_aux_set_z_orders (z_orders, 3, 1, 5, 0, 2, 4);
+                        }
+                    }
+                }
+            }
+            break;
+        case Box3D::Y:
+            if (!swapped) {
+                if (insideyz == 1) {
+                    box3d_aux_set_z_orders (z_orders, 2, 3, 1, 0, 5, 4);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 2, 3, 1, 5, 0, 4);
+                }
+            } else {
+                if (insideyx == 1) {
+                    box3d_aux_set_z_orders (z_orders, 4, 0, 5, 1, 3, 2);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 5, 0, 4, 1, 3, 2);
+                }
+            }
+            break;
+        case Box3D::Z:
+            if (!swapped) {
+                if (insidezy == 1) {
+                    box3d_aux_set_z_orders (z_orders, 2, 1, 0, 4, 3, 5);
+                } else if (insidexy == -1) {
+                    box3d_aux_set_z_orders (z_orders, 2, 1, 0, 5, 4, 3);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 2, 0, 1, 5, 3, 4);
+                }
+            } else {
+                box3d_aux_set_z_orders (z_orders, 3, 4, 5, 1, 0, 2);
+            }
+            break;
+        case Box3D::NONE:
+            if (!swapped) {
+                box3d_aux_set_z_orders (z_orders, 2, 3, 4, 1, 0, 5);
+            } else {
+                box3d_aux_set_z_orders (z_orders, 5, 0, 1, 4, 3, 2);
+            }
+            break;
+        default:
+            g_assert_not_reached();
+            break;
+    }
+}
+
+/*
+ * It can happen that during dragging the box is everted.
+ * In this case the opposite sides in this direction need to be swapped
+ */
+static Box3D::Axis
+box3d_everted_directions (SPBox3D *box) {
+    Box3D::Axis ev = Box3D::NONE;
+
+    box->orig_corner0.normalize();
+    box->orig_corner7.normalize();
+
+    if (box->orig_corner0[Proj::X] < box->orig_corner7[Proj::X])
+        ev = (Box3D::Axis) (ev ^ Box3D::X);
+    if (box->orig_corner0[Proj::Y] < box->orig_corner7[Proj::Y])
+        ev = (Box3D::Axis) (ev ^ Box3D::Y);
+    if (box->orig_corner0[Proj::Z] > box->orig_corner7[Proj::Z]) // FIXME: Remove the need to distinguish signs among the cases
+        ev = (Box3D::Axis) (ev ^ Box3D::Z);
+
+    return ev;
+}
+
+static void
+box3d_swap_sides(int z_orders[6], Box3D::Axis axis) {
+    int pos1 = -1;
+    int pos2 = -1;
+
+    for (int i = 0; i < 6; ++i) {
+        if (!(Box3D::int_to_face(z_orders[i]) & axis)) {
+            if (pos1 == -1) {
+                pos1 = i;
+            } else {
+                pos2 = i;
+                break;
+            }
+        }
+    }
+
+    if ((pos1 != -1) && (pos2 != -1)){
+        int tmp = z_orders[pos1];
+        z_orders[pos1] = z_orders[pos2];
+        z_orders[pos2] = tmp;
+    }
+}
+
+
+bool
+SPBox3D::recompute_z_orders () {
+    Persp3D *persp = this->get_perspective();
+
+    if (!persp)
+        return false;
+
+    int z_orders[6];
+
+    Geom::Point c3(this->get_corner_screen(3, false));
+
+    // determine directions from corner3 to the VPs
+    int num_finite = 0;
+    Box3D::Axis axis_finite = Box3D::NONE;
+    Box3D::Axis axis_infinite = Box3D::NONE;
+    Geom::Point dirs[3];
+    for (int i = 0; i < 3; ++i) {
+        dirs[i] = persp->get_PL_dir_from_pt(c3, Box3D::toProj(Box3D::axes[i]));
+        if (Persp3D::VP_is_finite(persp->perspective_impl, Proj::axes[i])) {
+            num_finite++;
+            axis_finite = Box3D::axes[i];
+        } else {
+            axis_infinite = Box3D::axes[i];
+        }
+    }
+
+    // determine the "central" axis (if there is one)
+    Box3D::Axis central_axis = Box3D::NONE;
+    if(Box3D::lies_in_sector(dirs[0], dirs[1], dirs[2])) {
+        central_axis = Box3D::Z;
+    } else if(Box3D::lies_in_sector(dirs[1], dirs[2], dirs[0])) {
+        central_axis = Box3D::X;
+    } else if(Box3D::lies_in_sector(dirs[2], dirs[0], dirs[1])) {
+        central_axis = Box3D::Y;
+    }
+
+    switch (num_finite) {
+        case 0:
+            // TODO: Remark: In this case (and maybe one of the others, too) the z-orders for all boxes
+            //               coincide, hence only need to be computed once in a more central location.
+            box3d_set_new_z_orders_case0(this, z_orders, central_axis);
+            break;
+        case 1:
+            box3d_set_new_z_orders_case1(this, z_orders, central_axis, axis_finite);
+            break;
+        case 2:
+        case 3:
+            box3d_set_new_z_orders_case2(this, z_orders, central_axis, axis_infinite);
+            break;
+        default:
+        /*
+         * For each VP F, check whether the half-line from the corner3 to F crosses the line segment
+         * joining the other two VPs. If this is the case, it determines the "central" corner from
+         * which the visible sides can be deduced. Otherwise, corner3 is the central corner.
+         */
+        // FIXME: We should eliminate the use of Geom::Point altogether
+        Box3D::Axis central_axis = Box3D::NONE;
+        Geom::Point vp_x = persp->get_VP(Proj::X).affine();
+        Geom::Point vp_y = persp->get_VP(Proj::Y).affine();
+        Geom::Point vp_z = persp->get_VP(Proj::Z).affine();
+        Geom::Point vpx(vp_x[Geom::X], vp_x[Geom::Y]);
+        Geom::Point vpy(vp_y[Geom::X], vp_y[Geom::Y]);
+        Geom::Point vpz(vp_z[Geom::X], vp_z[Geom::Y]);
+
+        Geom::Point c3 = this->get_corner_screen(3, false);
+        Geom::Point corner3(c3[Geom::X], c3[Geom::Y]);
+
+        if (box3d_half_line_crosses_joining_line (corner3, vpx, vpy, vpz)) {
+            central_axis = Box3D::X;
+        } else if (box3d_half_line_crosses_joining_line (corner3, vpy, vpz, vpx)) {
+            central_axis = Box3D::Y;
+        } else if (box3d_half_line_crosses_joining_line (corner3, vpz, vpx, vpy)) {
+            central_axis = Box3D::Z;
+        }
+
+        // FIXME: At present, this is not used.  Why is it calculated?
+        /*
+        unsigned int central_corner = 3 ^ central_axis;
+        if (central_axis == Box3D::Z) {
+            central_corner = central_corner ^ Box3D::XYZ;
+        }
+        if (box3d_XY_axes_are_swapped(this)) {
+            central_corner = central_corner ^ Box3D::XYZ;
+        }
+        */
+
+        Geom::Point c1(this->get_corner_screen(1, false));
+        Geom::Point c2(this->get_corner_screen(2, false));
+        Geom::Point c7(this->get_corner_screen(7, false));
+
+        Geom::Point corner1(c1[Geom::X], c1[Geom::Y]);
+        Geom::Point corner2(c2[Geom::X], c2[Geom::Y]);
+        Geom::Point corner7(c7[Geom::X], c7[Geom::Y]);
+        // FIXME: At present we don't use the information about central_corner computed above.
+        switch (central_axis) {
+            case Box3D::Y:
+                if (!box3d_half_line_crosses_joining_line(vpz, vpy, corner3, corner2)) {
+                    box3d_aux_set_z_orders (z_orders, 2, 3, 1, 5, 0, 4);
+                } else {
+                    // degenerate case
+                    box3d_aux_set_z_orders (z_orders, 2, 1, 3, 0, 5, 4);
+                }
+                break;
+
+            case Box3D::Z:
+                if (box3d_half_line_crosses_joining_line(vpx, vpz, corner3, corner1)) {
+                    // degenerate case
+                    box3d_aux_set_z_orders (z_orders, 2, 0, 1, 4, 3, 5);
+                } else if (box3d_half_line_crosses_joining_line(vpx, vpy, corner3, corner7)) {
+                    // degenerate case
+                    box3d_aux_set_z_orders (z_orders, 2, 1, 0, 5, 3, 4);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 2, 1, 0, 3, 4, 5);
+                }
+                break;
+
+            case Box3D::X:
+                if (box3d_half_line_crosses_joining_line(vpz, vpx, corner3, corner1)) {
+                    // degenerate case
+                    box3d_aux_set_z_orders (z_orders, 2, 1, 0, 4, 5, 3);
+                } else {
+                    box3d_aux_set_z_orders (z_orders, 2, 4, 0, 5, 1, 3);
+                }
+                break;
+
+            case Box3D::NONE:
+                box3d_aux_set_z_orders (z_orders, 2, 3, 4, 1, 0, 5);
+                break;
+
+            default:
+                g_assert_not_reached();
+                break;
+        } // end default case
+    }
+
+    // TODO: If there are still errors in z-orders of everted boxes, we need to choose a variable corner
+    //       instead of the hard-coded corner #3 in the computations above
+    Box3D::Axis ev = box3d_everted_directions(this);
+    for (auto & axe : Box3D::axes) {
+        if (ev & axe) {
+            box3d_swap_sides(z_orders, axe);
+        }
+    }
+
+    // Check whether anything actually changed
+    for (int i = 0; i < 6; ++i) {
+        if (this->z_orders[i] != z_orders[i]) {
+            for (int j = i; j < 6; ++j) {
+                this->z_orders[j] = z_orders[j];
+            }
+            return true;
+        }
+    }
+    return false;
+}
+
+static std::map<int, Box3DSide *> box3d_get_sides(SPBox3D *box)
+{
+    std::map<int, Box3DSide *> sides;
+    for (auto& obj: box->children) {
+        Box3DSide *side = dynamic_cast<Box3DSide *>(&obj);
+        if (side) {
+            sides[Box3D::face_to_int(side->getFaceId())] = side;
+        }
+    }
+    sides.erase(-1);
+    return sides;
+}
+
+
+// TODO: Check whether the box is everted in any direction and swap the sides opposite to this direction
+void
+SPBox3D::set_z_orders () {
+    // For efficiency reasons, we only set the new z-orders if something really changed
+    if (this->recompute_z_orders ()) {
+        std::map<int, Box3DSide *> sides = box3d_get_sides(this);
+        std::map<int, Box3DSide *>::iterator side;
+        for (int z_order : this->z_orders) {
+            side = sides.find(z_order);
+            if (side != sides.end()) {
+                ((*side).second)->lowerToBottom();
+            }
+        }
+    }
+}
+
+/*
+ * Auxiliary function for z-order recomputing:
+ * Determines whether \a pt lies in the sector formed by the two PLs from the corners with IDs
+ * \a i21 and \a id2 to the VP in direction \a axis. If the VP is infinite, we say that \a pt
+ * lies in the sector if it lies between the two (parallel) PLs.
+ * \ret *  0 if \a pt doesn't lie in the sector
+ *      *  1 if \a pt lies in the sector and either VP is finite of VP is infinite and the direction
+ *           from the edge between the two corners to \a pt points towards the VP
+ *      * -1 otherwise
+ */
+// TODO: Maybe it would be useful to have a similar method for projective points pt because then we
+//       can use it for VPs and perhaps merge the case distinctions during z-order recomputation.
+int
+SPBox3D::pt_lies_in_PL_sector (Geom::Point const &pt, int id1, int id2, Box3D::Axis axis) const {
+    Persp3D *persp = this->get_perspective();
+
+    // the two corners
+    Geom::Point c1(this->get_corner_screen(id1, false));
+    Geom::Point c2(this->get_corner_screen(id2, false));
+
+    int ret = 0;
+    if (Persp3D::VP_is_finite(persp->perspective_impl, Box3D::toProj(axis))) {
+        Geom::Point vp(persp->get_VP(Box3D::toProj(axis)).affine());
+        Geom::Point v1(c1 - vp);
+        Geom::Point v2(c2 - vp);
+        Geom::Point w(pt - vp);
+        ret = static_cast<int>(Box3D::lies_in_sector(v1, v2, w));
+    } else {
+        Box3D::PerspectiveLine pl1(c1, Box3D::toProj(axis), persp);
+        Box3D::PerspectiveLine pl2(c2, Box3D::toProj(axis), persp);
+        if (pl1.lie_on_same_side(pt, c2) && pl2.lie_on_same_side(pt, c1)) {
+            // test whether pt lies "towards" or "away from" the VP
+            Box3D::Line edge(c1,c2);
+            Geom::Point c3(this->get_corner_screen(id1 ^ axis, false));
+            if (edge.lie_on_same_side(pt, c3)) {
+                ret = 1;
+            } else {
+                ret = -1;
+            }
+        }
+    }
+    return ret;
+}
+
+int
+SPBox3D::VP_lies_in_PL_sector (Proj::Axis vpdir, int id1, int id2, Box3D::Axis axis) const {
+    Persp3D *persp = this->get_perspective();
+
+    if (!Persp3D::VP_is_finite(persp->perspective_impl, vpdir)) {
+        return 0;
+    } else {
+        return this->pt_lies_in_PL_sector(persp->get_VP(vpdir).affine(), id1, id2, axis);
+    }
+}
+
+/* swap the coordinates of corner0 and corner7 along the specified axis */
+static void
+box3d_swap_coords(SPBox3D *box, Proj::Axis axis, bool smaller = true) {
+    box->orig_corner0.normalize();
+    box->orig_corner7.normalize();
+    if ((box->orig_corner0[axis] < box->orig_corner7[axis]) != smaller) {
+        double tmp = box->orig_corner0[axis];
+        box->orig_corner0[axis] = box->orig_corner7[axis];
+        box->orig_corner7[axis] = tmp;
+    }
+    // Should we also swap the coordinates of save_corner0 and save_corner7?
+}
+
+/* ensure that the coordinates of corner0 and corner7 are in the correct order (to prevent everted boxes) */
+void
+SPBox3D::relabel_corners() {
+    box3d_swap_coords(this, Proj::X, false);
+    box3d_swap_coords(this, Proj::Y, false);
+    box3d_swap_coords(this, Proj::Z, true);
+}
+
+static void
+box3d_check_for_swapped_coords(SPBox3D *box, Proj::Axis axis, bool smaller) {
+    box->orig_corner0.normalize();
+    box->orig_corner7.normalize();
+
+    if ((box->orig_corner0[axis] < box->orig_corner7[axis]) != smaller) {
+        box->swapped = (Box3D::Axis) (box->swapped | Proj::toAffine(axis));
+    } else {
+        box->swapped = (Box3D::Axis) (box->swapped & ~Proj::toAffine(axis));
+    }
+}
+
+static void
+box3d_exchange_coords(SPBox3D *box) {
+    box->orig_corner0.normalize();
+    box->orig_corner7.normalize();
+
+    for (int i = 0; i < 3; ++i) {
+        if (box->swapped & Box3D::axes[i]) {
+            double tmp = box->orig_corner0[i];
+            box->orig_corner0[i] = box->orig_corner7[i];
+            box->orig_corner7[i] = tmp;
+        }
+    }
+}
+
+void
+SPBox3D::check_for_swapped_coords() {
+    box3d_check_for_swapped_coords(this, Proj::X, false);
+    box3d_check_for_swapped_coords(this, Proj::Y, false);
+    box3d_check_for_swapped_coords(this, Proj::Z, true);
+
+    box3d_exchange_coords(this);
+}
+
+static void box3d_extract_boxes_rec(SPObject *obj, std::list<SPBox3D *> &boxes) {
+    SPBox3D *box = dynamic_cast<SPBox3D *>(obj);
+    if (box) {
+        boxes.push_back(box);
+    } else if (dynamic_cast<SPGroup *>(obj)) {
+        for (auto& child: obj->children) {
+            box3d_extract_boxes_rec(&child, boxes);
+        }
+    }
+}
+
+std::list<SPBox3D *>
+SPBox3D::extract_boxes(SPObject *obj) {
+    std::list<SPBox3D *> boxes;
+    box3d_extract_boxes_rec(obj, boxes);
+    return boxes;
+}
+
+Persp3D *
+SPBox3D::get_perspective() const {
+    if(this->persp_ref) {
+        return this->persp_ref->getObject();
+    }
+    return nullptr;
+}
+
+void
+SPBox3D::switch_perspectives(Persp3D *old_persp, Persp3D *new_persp, bool recompute_corners) {
+    if (recompute_corners) {
+        this->orig_corner0.normalize();
+        this->orig_corner7.normalize();
+        double z0 = this->orig_corner0[Proj::Z];
+        double z7 = this->orig_corner7[Proj::Z];
+        Geom::Point corner0_screen = this->get_corner_screen(0, false);
+        Geom::Point corner7_screen = this->get_corner_screen(7, false);
+
+        this->orig_corner0 = new_persp->perspective_impl->tmat.preimage(corner0_screen, z0, Proj::Z);
+        this->orig_corner7 = new_persp->perspective_impl->tmat.preimage(corner7_screen, z7, Proj::Z);
+    }
+
+    old_persp->remove_box (this);
+    new_persp->add_box (this);
+
+    Glib::ustring href = "#";
+    href += new_persp->getId();
+    this->setAttribute("inkscape:perspectiveID", href);
+}
+
+/* Converts the 3D box to an ordinary SPGroup, adds it to the XML tree at the same position as
+   the original box and deletes the latter */
+SPGroup *SPBox3D::convert_to_group()
+{
+    SPDocument *doc = this->document;
+    Inkscape::XML::Document *xml_doc = doc->getReprDoc();
+
+    // remember position of the box
+    int pos = this->getPosition();
+
+    // remember important attributes
+    gchar const *id = this->getAttribute("id");
+    gchar const *style = this->getAttribute("style");
+    gchar const *mask = this->getAttribute("mask");
+    gchar const *clip_path = this->getAttribute("clip-path");
+
+    // create a new group and add the sides (converted to ordinary paths) as its children
+    Inkscape::XML::Node *grepr = xml_doc->createElement("svg:g");
+
+    for (auto& obj: this->children) {
+        Box3DSide *side = dynamic_cast<Box3DSide *>(&obj);
+        if (side) {
+            Inkscape::XML::Node *repr = side->convert_to_path();
+            grepr->appendChild(repr);
+        } else {
+            g_warning("Non-side item encountered as child of a 3D box.");
+        }
+    }
+
+    // add the new group to the box's parent and set remembered position
+    SPObject *parent = this->parent;
+    parent->appendChild(grepr);
+    grepr->setPosition(pos);
+    grepr->setAttributeOrRemoveIfEmpty("style", style);
+    grepr->setAttributeOrRemoveIfEmpty("mask", mask);
+    grepr->setAttributeOrRemoveIfEmpty("clip-path", clip_path);
+
+    this->deleteObject(true);
+
+    grepr->setAttribute("id", id);
+
+    SPGroup *group = dynamic_cast<SPGroup *>(doc->getObjectByRepr(grepr));
+    g_assert(group != nullptr);
+    return group;
+}
+
+const char *SPBox3D::displayName() const {
+    return _("3D Box");
+}
+
+gchar *SPBox3D::description() const {
+    // We could put more details about the 3d box here
+    return g_strdup("");
+}
+
+static inline void
+box3d_push_back_corner_pair(SPBox3D const *box, std::list<std::pair<Geom::Point, Geom::Point> > &pts, int c1, int c2) {
+    pts.emplace_back(box->get_corner_screen(c1, false),
+                     box->get_corner_screen(c2, false));
+}
+
+void SPBox3D::convert_to_guides() const {
+    Inkscape::Preferences *prefs = Inkscape::Preferences::get();
+
+    if (!prefs->getBool("/tools/shapes/3dbox/convertguides", true)) {
+        this->convert_to_guides();
+        return;
+    }
+
+    std::list<std::pair<Geom::Point, Geom::Point> > pts;
+
+    /* perspective lines in X direction */
+    box3d_push_back_corner_pair(this, pts, 0, 1);
+    box3d_push_back_corner_pair(this, pts, 2, 3);
+    box3d_push_back_corner_pair(this, pts, 4, 5);
+    box3d_push_back_corner_pair(this, pts, 6, 7);
+
+    /* perspective lines in Y direction */
+    box3d_push_back_corner_pair(this, pts, 0, 2);
+    box3d_push_back_corner_pair(this, pts, 1, 3);
+    box3d_push_back_corner_pair(this, pts, 4, 6);
+    box3d_push_back_corner_pair(this, pts, 5, 7);
+
+    /* perspective lines in Z direction */
+    box3d_push_back_corner_pair(this, pts, 0, 4);
+    box3d_push_back_corner_pair(this, pts, 1, 5);
+    box3d_push_back_corner_pair(this, pts, 2, 6);
+    box3d_push_back_corner_pair(this, pts, 3, 7);
+
+    sp_guide_pt_pairs_to_guides(this->document, pts);
+}
+
+/*
+  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 :