Add optional hops where wires cross (#436)

Where two wires cross without being connected, a project can now draw a
small arc (a hop) on one of them, instead of the user inserting a jump
symbol and splitting the wire. It is a project setting, off by default:
Project properties > Général > "Croisements de conducteurs", with no
hops, hops on horizontal wires, or hops on vertical wires. Choosing the
orientation rather than following drawing order keeps a project
consistent.

Only the drawing changes: no element is added and no wire is split. A
wire that ends or bends on another one is a junction and never hops,
and a crossing too close to the end of a segment for the arc to fit is
drawn plainly. PDF, SVG and image export and printing show the hops,
since they paint through Conductor::paint(); DXF export, which writes
the segments itself, does not.

The setting is saved as <wire_crossings hop="..."/> under the project
root, next to <usage>, and only when hops are on, so a project that
never used them saves exactly as before.

The geometry is in wirehops.cpp, free of any graphics item, and tested
on its own. Conductor::paintedPath() feeds it the conductors of the
folio from a snapshot of their scene points, rebuilt only when a
conductor changes shape, moves, or enters or leaves a folio; each hop
path is cached the same way. Asking the scene for the conductors in a
rect instead strokes every candidate's shape, which made a 366-wire
folio render 0.6 s slower; with the snapshot the difference is within
measurement noise.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmake/qet_compilation_vars.cmake

@@ -177,6 +177,8 @@ set(QET_SRC_FILES
   ${QET_DIR}/sources/conductornumexport.cpp
   ${QET_DIR}/sources/wiringlistexport.h
   ${QET_DIR}/sources/wiringlistexport.cpp
+  ${QET_DIR}/sources/wirehops.h
+  ${QET_DIR}/sources/wirehops.cpp
   ${QET_DIR}/sources/ui/wiringlistdialog.h
   ${QET_DIR}/sources/ui/wiringlistdialog.cpp
   ${QET_DIR}/sources/conductornumexport.h

sources/qetgraphicsitem/conductor.cpp

@@ -32,10 +32,34 @@
 #include "element.h"
 #include "../QetGraphicsItemModeler/qetgraphicshandleritem.h"
 #include "../utils/qetutils.h"
+#include "../wirehops.h"
 
 #include <QMultiHash>
 #include <QtDebug>
 
+namespace {
+		//Bumped whenever a conductor changes shape, moves, or enters or
+		//leaves a folio: the hops of every conductor may then change.
+		//0 is never current, so a fresh cache is always rebuilt.
+	quint64 s_conductor_geometry_generation = 1;
+	void conductorGeometryChanged() { ++s_conductor_geometry_generation; }
+
+		//The conductors of the last folio whose hops were computed, as
+		//scene points and plain path bounds. Rebuilt only when the folio
+		//or the generation changes, so a repaint (pan, zoom, selection)
+		//costs no scene query: asking the scene for the conductors in a
+		//rect strokes each one's shape, and on a folio of a few hundred
+		//conductors that made every repaint 0.6 s slower.
+	struct HopCandidate {
+		const Conductor *conductor;
+		QRectF rect;
+		QVector<QPointF> points;
+	};
+	const Diagram *s_hop_candidates_diagram = nullptr;
+	quint64 s_hop_candidates_generation = 0;
+	QVector<HopCandidate> s_hop_candidates;
+}
+
 #define PR(x) qDebug() << #x " = " << x;
 
 bool Conductor::pen_and_brush_initialized = false;
@@ -147,6 +171,7 @@ Conductor::Conductor(Terminal *p1, Terminal* p2) :
 */
 Conductor::~Conductor()
 {
+	conductorGeometryChanged();
 	removeHandler();
 	terminal1->removeConductor(this);
 	terminal2->removeConductor(this);
@@ -602,8 +627,9 @@ void Conductor::paint(QPainter *painter, const QStyleOptionGraphicsItem *options
 
 	painter -> setPen(final_conductor_pen);
 
-		//Draw the conductor
-	painter -> drawPath(path());
+		//Draw the conductor, with a hop at each crossing if the project asks for them
+	const QPainterPath painted_path = paintedPath();
+	painter -> drawPath(painted_path);
 		//Draw the second color
 	if(m_properties.m_bicolor)
 	{
@@ -614,7 +640,7 @@ void Conductor::paint(QPainter *painter, const QStyleOptionGraphicsItem *options
 		final_conductor_pen.setDashPattern(dash_pattern);
 		painter->save();
 		painter->setPen(final_conductor_pen);
-		painter->drawPath(path());
+		painter->drawPath(painted_path);
 		painter->restore();
 	}
 
@@ -790,6 +816,7 @@ QVariant Conductor::itemChange(GraphicsItemChange change, const QVariant &value)
 	}
 	else if (change == QGraphicsItem::ItemSceneHasChanged)
 	{
+		conductorGeometryChanged();
 		calculateTextItemPosition();
 
 		if(!scene())
@@ -803,6 +830,9 @@ QVariant Conductor::itemChange(GraphicsItemChange change, const QVariant &value)
 	else if (change == QGraphicsItem::ItemPositionHasChanged && isSelected()) {
 		adjustHandlerPos();
 	}
+	else if (change == QGraphicsItem::ItemScenePositionHasChanged) {
+		conductorGeometryChanged();
+	}
 
 	return(QGraphicsObject::itemChange(change, value));
 }
@@ -1657,6 +1687,7 @@ void Conductor::setPath(const QPainterPath &path)
 
 	prepareGeometryChange();
 	m_path = path;
+	conductorGeometryChanged();
 	update();
 }
 
@@ -1942,6 +1973,87 @@ bool isContained(const QPointF &a, const QPointF &b, const QPointF &c) {
 	);
 }
 
+/**
+	@brief Conductor::paintedPath
+	@return the path drawn for this conductor: path(), with a hop at each
+	place it crosses another conductor when the project draws hops
+	(issue #436, QETProject::wireHops()). Cached until a conductor changes
+	shape, moves, or enters or leaves a folio, so a repaint costs nothing.
+	A moved conductor still repaints the hops of the others: a crossing
+	lies inside the bounding rect of both conductors, which Qt repaints
+	when either moves.
+*/
+QPainterPath Conductor::paintedPath() const
+{
+	const Diagram *parent_diagram = diagram();
+	if (!parent_diagram || !parent_diagram->project()) {
+		return path();
+	}
+	const WireHops::Mode mode = parent_diagram->project()->wireHops();
+	if (mode == WireHops::Mode::None) {
+		return path();
+	}
+	if (m_hops_generation == s_conductor_geometry_generation
+		&& m_hops_mode == int(mode)) {
+		return m_hops_path;
+	}
+
+	if (s_hop_candidates_diagram != parent_diagram
+		|| s_hop_candidates_generation != s_conductor_geometry_generation)
+	{
+		s_hop_candidates.clear();
+		const QList<Conductor *> conductors = parent_diagram->conductors();
+		for (const Conductor *conductor : conductors)
+		{
+			HopCandidate candidate;
+			candidate.conductor = conductor;
+			candidate.rect = conductor->mapRectToScene(conductor->path().boundingRect());
+			for (const QPointF &point : conductor->segmentsToPoints()) {
+				candidate.points.append(conductor->mapToScene(point));
+			}
+			s_hop_candidates.append(candidate);
+		}
+		s_hop_candidates_diagram = parent_diagram;
+		s_hop_candidates_generation = s_conductor_geometry_generation;
+	}
+
+	m_hops_path = path();
+	m_hops_generation = s_conductor_geometry_generation;
+	m_hops_mode = int(mode);
+
+	const QList<QPointF> points = segmentsToPoints();
+	if (points.size() < 2) {
+		return m_hops_path;
+	}
+	QVector<QPointF> wire;
+	for (const QPointF &point : points) {
+		wire.append(mapToScene(point));
+	}
+
+		//A conductor crossing this one has path bounds overlapping its own;
+		//adjusted by 1 because a straight conductor's bounds have no width
+	const QRectF rect = mapRectToScene(path().boundingRect()).adjusted(-1, -1, 1, 1);
+	QList<QVector<QPointF>> others;
+	for (const HopCandidate &candidate : std::as_const(s_hop_candidates))
+	{
+		if (candidate.conductor != this
+			&& rect.intersects(candidate.rect.adjusted(-1, -1, 1, 1))) {
+			others.append(candidate.points);
+		}
+	}
+
+	const QList<QPointF> scene_hops = WireHops::crossings(wire, others, mode);
+	if (!scene_hops.isEmpty())
+	{
+		QList<QPointF> hops;
+		for (const QPointF &hop : scene_hops) {
+			hops.append(mapFromScene(hop));
+		}
+		m_hops_path = WireHops::path(QVector<QPointF>(points.begin(), points.end()), hops, mode);
+	}
+	return m_hops_path;
+}
+
 /**
 	@return la liste des positions des jonctions avec d'autres conducteurs
 */

sources/qetgraphicsitem/conductor.h

@@ -143,6 +143,7 @@ class Conductor : public QGraphicsObject
 		void setSequenceNum(const autonum::sequentialNumbers& sn);
 
 		QList<QPointF> junctions() const;
+		QPainterPath paintedPath() const;
 
 	private:
 		void setUpConnectionForFormula(
@@ -187,6 +188,10 @@ class Conductor : public QGraphicsObject
 		QVector<QetGraphicsHandlerItem *> m_handler_vector;
 		int m_vector_index = -1;
 		bool m_mouse_over;
+			///Hop path cache for paintedPath(), valid while no conductor geometry changed
+		mutable QPainterPath m_hops_path;
+		mutable quint64 m_hops_generation = 0;
+		mutable int m_hops_mode = -1;
 			/// Functional properties
 		ConductorProperties m_properties;
 			/// Text input for non simple, non-singleline conductors

sources/qetproject.cpp

@@ -1232,6 +1232,31 @@ void QETProject::setAutoConductor(bool ac)
 		m_auto_conductor = ac;
 }
 
+/**
+	@brief QETProject::wireHops
+	@return which wire of a crossing draws a hop (issue #436),
+	WireHops::Mode::None when crossings are drawn as plain lines.
+*/
+WireHops::Mode QETProject::wireHops() const {
+	return m_wire_hops;
+}
+
+/**
+	@brief QETProject::setWireHops
+	Set which wire of a crossing draws a hop, and redraw every folio.
+	@param mode
+*/
+void QETProject::setWireHops(WireHops::Mode mode)
+{
+	if (mode == m_wire_hops) {
+		return;
+	}
+	m_wire_hops = mode;
+	for (Diagram *diagram : diagrams()) {
+		diagram->update();
+	}
+}
+
 /**
 	@brief QETProject::autoBreakConductor
 	@return true if use of auto break conductor is authorized.
@@ -1341,6 +1366,7 @@ QDomDocument QETProject::toXml()
 
 	// local, non-transmitted usage tracking (time spent on this project)
 	writeUsageXml(project_root);
+	writeWireHopsXml(project_root);
 
 	// Properties for news diagrams
 	QDomElement new_diagrams_properties = xml_doc.createElement("newdiagrams");
@@ -1850,6 +1876,7 @@ void QETProject::readProjectXml(QDomDocument &xml_project)
 
 		//Load the local, non-transmitted usage tracking
 	readUsageXml(xml_project);
+	readWireHopsXml(xml_project);
 
 		//Load the default properties for the new diagrams
 	readDefaultPropertiesXml(xml_project);
@@ -2028,6 +2055,21 @@ void QETProject::readUsageXml(QDomDocument &xml_project)
 	m_project_properties_handler.usageTracker().fromXml(xml_project.documentElement());
 }
 
+/**
+	@brief QETProject::readWireHopsXml
+	Read the <wire_crossings> element of the project, if any.
+	A project without it draws no hop.
+	@param xml_project : the xml description of the project
+*/
+void QETProject::readWireHopsXml(QDomDocument &xml_project)
+{
+	const QDomElement crossings = xml_project.documentElement()
+			.firstChildElement(QStringLiteral("wire_crossings"));
+	m_wire_hops = crossings.isNull()
+			? WireHops::Mode::None
+			: WireHops::fromString(crossings.attribute(QStringLiteral("hop")));
+}
+
 /**
 	@brief QETProject::readDefaultPropertiesXml
 	load default properties for new diagram, found in the xml of this project
@@ -2173,6 +2215,23 @@ void QETProject::writeUsageXml(QDomElement &xml_element) {
 	m_project_properties_handler.usageTracker().toXml(xml_element);
 }
 
+/**
+	@brief QETProject::writeWireHopsXml
+	Export which wire of a crossing hops as a <wire_crossings> child of
+	\a xml_element. Written only when hops are on, so a project that never
+	used them saves exactly as before.
+*/
+void QETProject::writeWireHopsXml(QDomElement &xml_element)
+{
+	if (m_wire_hops == WireHops::Mode::None) {
+		return;
+	}
+	QDomElement crossings = xml_element.ownerDocument()
+			.createElement(QStringLiteral("wire_crossings"));
+	crossings.setAttribute(QStringLiteral("hop"), WireHops::toString(m_wire_hops));
+	xml_element.appendChild(crossings);
+}
+
 /**
 	@brief QETProject::writeDefaultPropertiesXml
 	Export all defaults properties used by a new diagram and his content

sources/qetproject.h

@@ -28,6 +28,7 @@
 #include "properties/xrefproperties.h"
 #include "titleblock/templatescollection.h"
 #include "titleblockproperties.h"
+#include "wirehops.h"
 #include "diagram.h"
 #ifdef BUILD_WITHOUT_KF
 #	include "ui/nokde/kautosavefile.h"
@@ -208,6 +209,8 @@ class QETProject : public QObject
 		bool autoElement () const;
 		bool autoFolio () const;
 		void setAutoConductor (bool ac);
+		WireHops::Mode wireHops() const;
+		void setWireHops(WireHops::Mode mode);
 		void setAutoBreakConductor (bool abc);
 		void setAutoElement (bool ae);
 		void autoFolioNumberingNewFolios ();
@@ -304,10 +307,12 @@ class QETProject : public QObject
 		void readDefaultPropertiesXml(QDomDocument &xml_project);
 		void readTerminalStripXml(const QDomDocument &xml_project);
 		void readUsageXml(QDomDocument &xml_project);
+		void readWireHopsXml(QDomDocument &xml_project);
 
 		void writeProjectPropertiesXml(QDomElement &);
 		void writeDefaultPropertiesXml(QDomElement &);
 		void writeUsageXml(QDomElement &);
+		void writeWireHopsXml(QDomElement &);
 		void addDiagram(Diagram *diagram, int pos = -1);
 		void detachDiagram(Diagram *diagram);
 		void writeBackup();
@@ -365,6 +370,7 @@ class QETProject : public QObject
 		QHash <QString, NumerotationContext> m_element_autonum; //Title and NumContext hash
 		QString m_current_element_autonum;
 		bool m_auto_conductor = true;
+		WireHops::Mode m_wire_hops = WireHops::Mode::None;
 	bool m_auto_break_conductor = false;
 		XmlElementCollection *m_elements_collection = nullptr;
 		bool m_freeze_new_elements = false;

sources/ui/configpage/projectconfigpages.cpp

@@ -170,6 +170,12 @@ void ProjectMainConfigPage::applyProjectConf()
 		modified_project = true;
 	}
 
+	const auto wire_hops = WireHops::fromString(wire_hops_cb_ -> currentData().toString());
+	if (m_project -> wireHops() != wire_hops) {
+		m_project -> setWireHops(wire_hops);
+		modified_project = true;
+	}
+
 	if (modified_project) {
 		m_project -> setModified(true);
 	}
@@ -206,6 +212,19 @@ void ProjectMainConfigPage::initWidgets()
 	usage_enabled_cb_ = new QCheckBox(tr("Suivre le temps passé sur ce projet (uniquement enregistré localement dans ce fichier)", "checkbox label"));
 	usage_reset_pb_ = new QPushButton(tr("Réinitialiser", "button label"));
 	connect(usage_reset_pb_, &QPushButton::clicked, this, &ProjectMainConfigPage::resetUsageTracker);
+
+		//Hops where two conductors cross without being connected (issue #436)
+	wire_hops_label_ = new QLabel(tr("Croisements de conducteurs :", "label when configuring"));
+	wire_hops_cb_ = new QComboBox();
+	wire_hops_cb_ -> addItem(tr("Sans saut", "wire crossings"),
+							 WireHops::toString(WireHops::Mode::None));
+	wire_hops_cb_ -> addItem(tr("Saut sur les conducteurs horizontaux", "wire crossings"),
+							 WireHops::toString(WireHops::Mode::Horizontal));
+	wire_hops_cb_ -> addItem(tr("Saut sur les conducteurs verticaux", "wire crossings"),
+							 WireHops::toString(WireHops::Mode::Vertical));
+	wire_hops_cb_ -> setToolTip(tr("Dessine un petit arc là où deux conducteurs se croisent sans être reliés. "
+								   "Seul le dessin change : aucun élément n'est ajouté et aucun conducteur n'est coupé.",
+								   "tooltip"));
 }
 
 /**
@@ -231,6 +250,13 @@ void ProjectMainConfigPage::initLayout()
 	usage_layout0 -> addWidget(usage_reset_pb_);
 	main_layout0 -> addLayout(usage_layout0);
 	main_layout0 -> addWidget(usage_enabled_cb_);
+	main_layout0 -> addSpacing(10);
+
+	QHBoxLayout *wire_hops_layout0 = new QHBoxLayout();
+	wire_hops_layout0 -> addWidget(wire_hops_label_);
+	wire_hops_layout0 -> addWidget(wire_hops_cb_);
+	wire_hops_layout0 -> addStretch();
+	main_layout0 -> addLayout(wire_hops_layout0);
 
 	setLayout(main_layout0);
 	this -> setMinimumWidth(680);
@@ -251,6 +277,9 @@ void ProjectMainConfigPage::readValuesFromProject()
 							 .arg(total_seconds / 3600)
 							 .arg((total_seconds % 3600) / 60));
 	usage_enabled_cb_ -> setChecked(usage_tracker.isEnabled());
+
+	const int wire_hops_index = wire_hops_cb_ -> findData(WireHops::toString(m_project -> wireHops()));
+	wire_hops_cb_ -> setCurrentIndex(qMax(0, wire_hops_index));
 }
 
 /**
@@ -277,6 +306,7 @@ void ProjectMainConfigPage::adjustReadOnly()
 	title_value_ -> setReadOnly(is_read_only);
 	usage_enabled_cb_ -> setDisabled(is_read_only);
 	usage_reset_pb_ -> setDisabled(is_read_only);
+	wire_hops_cb_ -> setDisabled(is_read_only);
 }
 
 //######################################################################################//

sources/ui/configpage/projectconfigpages.h

@@ -20,6 +20,7 @@
 #include "configpage.h"
 
 class QLabel;
+class QComboBox;
 class QLineEdit;
 class QCheckBox;
 class QPushButton;
@@ -125,6 +126,8 @@ class ProjectMainConfigPage : public ProjectConfigPage {
 	QLabel *usage_value_;
 	QCheckBox *usage_enabled_cb_;
 	QPushButton *usage_reset_pb_;
+	QLabel *wire_hops_label_;
+	QComboBox *wire_hops_cb_;
 };
 
 class ProjectAutoNumConfigPage : public ProjectConfigPage {

sources/wirehops.cpp

@@ -0,0 +1,211 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include "wirehops.h"
+
+#include <QtMath>
+#include <algorithm>
+
+namespace {
+		//Coordinates closer than this are the same; points are on a grid
+	constexpr qreal tolerance = 0.01;
+
+	bool isHorizontal(const QPointF &a, const QPointF &b) {
+		return qAbs(a.y() - b.y()) < tolerance && qAbs(a.x() - b.x()) >= tolerance;
+	}
+
+	bool isVertical(const QPointF &a, const QPointF &b) {
+		return qAbs(a.x() - b.x()) < tolerance && qAbs(a.y() - b.y()) >= tolerance;
+	}
+
+		//True if @a value is strictly between @a a and @a b, by more than @a margin
+	bool strictlyBetween(qreal value, qreal a, qreal b, qreal margin) {
+		return value > qMin(a, b) + margin && value < qMax(a, b) - margin;
+	}
+
+		//The hops of @a hops lying on the segment @a a - @a b, ordered from @a a
+	QList<QPointF> hopsOnSegment(const QPointF &a, const QPointF &b,
+								 const QList<QPointF> &hops, bool horizontal)
+	{
+		QList<QPointF> on_segment;
+		for (const QPointF &hop : hops)
+		{
+			if (horizontal
+				? (qAbs(hop.y() - a.y()) < tolerance && strictlyBetween(hop.x(), a.x(), b.x(), 0))
+				: (qAbs(hop.x() - a.x()) < tolerance && strictlyBetween(hop.y(), a.y(), b.y(), 0)))
+			{
+				on_segment.append(hop);
+			}
+		}
+		std::sort(on_segment.begin(), on_segment.end(), [&a](const QPointF &p, const QPointF &q) {
+			return QLineF(a, p).length() < QLineF(a, q).length();
+		});
+		return on_segment;
+	}
+}
+
+/**
+	@brief WireHops::toString
+	@return the value written in the project file for @a mode
+*/
+QString WireHops::toString(Mode mode)
+{
+	switch (mode) {
+		case Mode::Horizontal: return QStringLiteral("horizontal");
+		case Mode::Vertical:   return QStringLiteral("vertical");
+		case Mode::None:       break;
+	}
+	return QStringLiteral("none");
+}
+
+/**
+	@brief WireHops::fromString
+	@return the mode written as @a string in a project file,
+	Mode::None for anything else, so an unknown value draws no hop.
+*/
+WireHops::Mode WireHops::fromString(const QString &string)
+{
+	if (string == QLatin1String("horizontal")) return Mode::Horizontal;
+	if (string == QLatin1String("vertical"))   return Mode::Vertical;
+	return Mode::None;
+}
+
+/**
+	@brief WireHops::crossings
+	@param wire : the points of the wire, in scene coordinates
+	@param others : the points of every other wire that may cross it,
+	in scene coordinates
+	@param mode : which wire of a crossing hops
+	@return the points where @a wire hops, in the order of @a wire.
+
+	A crossing is kept only if it lies strictly inside the segment of the
+	other wire (a wire ending or bending on this one is a junction, not a
+	crossing) and at least one hop radius from the ends of this wire's
+	segment, so the arc fits. Of two crossings closer than one arc
+	width, only the first hops.
+*/
+QList<QPointF> WireHops::crossings(const QVector<QPointF> &wire,
+								   const QList<QVector<QPointF>> &others,
+								   Mode mode)
+{
+	QList<QPointF> hops;
+	if (mode == Mode::None || wire.size() < 2) {
+		return hops;
+	}
+
+	const bool horizontal = mode == Mode::Horizontal;
+	for (int i = 0 ; i < wire.size() - 1 ; ++i)
+	{
+		const QPointF a = wire.at(i);
+		const QPointF b = wire.at(i + 1);
+		if (horizontal ? !isHorizontal(a, b) : !isVertical(a, b)) {
+			continue;
+		}
+
+		QList<QPointF> on_segment;
+		for (const auto &other : others)
+		{
+			for (int j = 0 ; j < other.size() - 1 ; ++j)
+			{
+				const QPointF c = other.at(j);
+				const QPointF d = other.at(j + 1);
+				if (horizontal ? !isVertical(c, d) : !isHorizontal(c, d)) {
+					continue;
+				}
+
+				const QPointF crossing = horizontal ? QPointF(c.x(), a.y())
+													: QPointF(a.x(), c.y());
+				const bool inside_wire = horizontal
+						? strictlyBetween(crossing.x(), a.x(), b.x(), radius)
+						: strictlyBetween(crossing.y(), a.y(), b.y(), radius);
+				const bool inside_other = horizontal
+						? strictlyBetween(crossing.y(), c.y(), d.y(), tolerance)
+						: strictlyBetween(crossing.x(), c.x(), d.x(), tolerance);
+				if (inside_wire && inside_other) {
+					on_segment.append(crossing);
+				}
+			}
+		}
+
+		std::sort(on_segment.begin(), on_segment.end(), [&a](const QPointF &p, const QPointF &q) {
+			return QLineF(a, p).length() < QLineF(a, q).length();
+		});
+		for (const QPointF &crossing : std::as_const(on_segment))
+		{
+			if (!hops.isEmpty()
+				&& QLineF(hops.last(), crossing).length() < 2 * radius + tolerance) {
+				continue;
+			}
+			hops.append(crossing);
+		}
+	}
+	return hops;
+}
+
+/**
+	@brief WireHops::path
+	@param wire : the points of the wire
+	@param hops : the points where the wire hops, from WireHops::crossings,
+	in the same coordinates as @a wire
+	@param mode : which wire of a crossing hops
+	@return the path of the wire, with a half circle at each hop: above a
+	horizontal wire, right of a vertical one. With no hop, the same path
+	as the plain wire.
+*/
+QPainterPath WireHops::path(const QVector<QPointF> &wire,
+							const QList<QPointF> &hops,
+							Mode mode)
+{
+	QPainterPath path;
+	if (wire.isEmpty()) {
+		return path;
+	}
+
+	const bool horizontal = mode == Mode::Horizontal;
+	path.moveTo(wire.first());
+	for (int i = 0 ; i < wire.size() - 1 ; ++i)
+	{
+		const QPointF a = wire.at(i);
+		const QPointF b = wire.at(i + 1);
+		const bool hops_here = mode != Mode::None
+				&& (horizontal ? isHorizontal(a, b) : isVertical(a, b));
+
+		if (hops_here)
+		{
+				//1 when the wire runs towards +x (or +y), -1 otherwise
+			const qreal direction = horizontal ? (b.x() > a.x() ? 1 : -1)
+											   : (b.y() > a.y() ? 1 : -1);
+			for (const QPointF &hop : hopsOnSegment(a, b, hops, horizontal))
+			{
+				const QRectF circle(hop.x() - radius, hop.y() - radius,
+									2 * radius, 2 * radius);
+				if (horizontal) {
+						//Over the top: from the left end to the right one, or back
+					path.lineTo(hop.x() - direction * radius, hop.y());
+					path.arcTo(circle, direction > 0 ? 180 : 0, direction > 0 ? -180 : 180);
+				} else {
+						//On the right: from the top end to the bottom one, or back
+					path.lineTo(hop.x(), hop.y() - direction * radius);
+					path.arcTo(circle, direction > 0 ? 90 : 270, direction > 0 ? -180 : 180);
+				}
+			}
+		}
+		path.lineTo(b);
+	}
+	return path;
+}

sources/wirehops.h

@@ -0,0 +1,63 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef WIREHOPS_H
+#define WIREHOPS_H
+
+#include <QList>
+#include <QPainterPath>
+#include <QPointF>
+#include <QString>
+#include <QVector>
+
+/**
+	@brief The WireHops namespace
+	Hops (small arcs) drawn where two wires cross without being connected
+	(issue #436). Only the drawing changes: no element is added and no wire
+	is split. Kept free of any QGraphicsItem so the geometry can be tested
+	on its own.
+
+	Wires in QElectroTech are made of horizontal and vertical segments
+	only, so a crossing is a segment of one orientation passing through a
+	segment of the other, away from the ends of both. A wire that ends or
+	bends on another one is a junction, not a crossing, and never hops.
+*/
+namespace WireHops
+{
+		///Which wire of a crossing draws the hop
+	enum class Mode {
+		None,       ///< no hop, the default: crossings are drawn as plain lines
+		Horizontal, ///< the horizontal wire hops over the vertical one
+		Vertical    ///< the vertical wire hops over the horizontal one
+	};
+
+		///Radius of a hop, in scene units (a grid step is 10)
+	constexpr qreal radius = 4.0;
+
+	QString toString(Mode mode);
+	Mode fromString(const QString &string);
+
+	QList<QPointF> crossings(const QVector<QPointF> &wire,
+							 const QList<QVector<QPointF>> &others,
+							 Mode mode);
+	QPainterPath path(const QVector<QPointF> &wire,
+					  const QList<QPointF> &hops,
+					  Mode mode);
+}
+
+#endif // WIREHOPS_H

tests/qttest/CMakeLists.txt

@@ -376,6 +376,20 @@ target_compile_definitions(tst_wiringlistexport PRIVATE
   "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\""
   "QET_EXAMPLES_DIR=\"${QET_DIR}/examples\"")
 
+# Hops where wires cross (issue #436): the geometry in wirehops.cpp, and
+# through the real binary, that --resave keeps the project setting and
+# adds nothing to a project without it.
+add_executable(
+  tst_wirehops
+  tst_wirehops.cpp
+  ${QET_DIR}/sources/wirehops.cpp)
+add_test(NAME tst_wirehops COMMAND tst_wirehops)
+add_dependencies(tst_wirehops qelectrotech)
+target_include_directories(tst_wirehops PRIVATE ${QET_DIR}/sources)
+target_link_libraries(tst_wirehops PRIVATE Qt::Test Qt::Gui)
+target_compile_definitions(tst_wirehops PRIVATE
+  "QET_TEST_BINARY_PATH=\"$<TARGET_FILE:qelectrotech>\"")
+
 # qet.conductorUuids() / qet.conductorEnds(): a script lists a folio's
 # conductors by uuid and finds each one's two ends. Runs a script through
 # the real binary's --run on fixtures/qet_bug_repro_resaved.qet, so only

tests/qttest/tst_wirehops.cpp

@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <QtTest>
+
+#include <QDir>
+#include <QFile>
+#include <QProcess>
+#include <QProcessEnvironment>
+#include <QTemporaryDir>
+
+#include "wirehops.h"
+
+// Hops where two wires cross (issue #436). The geometry is tested on its
+// own; the project setting is tested through the real binary: --resave
+// must keep a <wire_crossings> element, and must not add one to a project
+// that never had it, so existing projects save exactly as before.
+class tst_wirehops : public QObject
+{
+	Q_OBJECT
+
+	using Mode = WireHops::Mode;
+	QTemporaryDir m_dir;
+	int m_run = 0;
+
+	static QVector<QPointF> line(QPointF a, QPointF b) { return {a, b}; }
+
+		// Runs --resave on @p in, returns the saved file's text (empty on failure)
+	QString resave(const QString &in)
+	{
+		const QString home = m_dir.filePath(QStringLiteral("home%1").arg(m_run));
+		const QString tmp = m_dir.filePath(QStringLiteral("tmp%1").arg(m_run));
+		const QString out = m_dir.filePath(QStringLiteral("out%1.qet").arg(m_run++));
+		QDir().mkpath(home);
+		QDir().mkpath(tmp);
+		QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
+		env.insert(QStringLiteral("QT_QPA_PLATFORM"), QStringLiteral("offscreen"));
+		env.insert(QStringLiteral("HOME"), home);
+		env.insert(QStringLiteral("XDG_CONFIG_HOME"), home + QStringLiteral("/.config"));
+		env.insert(QStringLiteral("XDG_DATA_HOME"), home + QStringLiteral("/.local/share"));
+		env.insert(QStringLiteral("TMPDIR"), tmp);
+
+		QProcess proc;
+		proc.setProcessEnvironment(env);
+		proc.start(QStringLiteral(QET_TEST_BINARY_PATH), {QStringLiteral("--resave"), in, out});
+		if (!proc.waitForFinished(120000) || proc.exitCode() != 0)
+			return {};
+		QFile file(out);
+		if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
+			return {};
+		return QString::fromUtf8(file.readAll());
+	}
+
+private slots:
+	void initTestCase()
+	{
+		QVERIFY(m_dir.isValid());
+	}
+
+	void modeNames()
+	{
+		QCOMPARE(int(WireHops::fromString(WireHops::toString(Mode::Horizontal))), int(Mode::Horizontal));
+		QCOMPARE(int(WireHops::fromString(WireHops::toString(Mode::Vertical))), int(Mode::Vertical));
+		QCOMPARE(int(WireHops::fromString(WireHops::toString(Mode::None))), int(Mode::None));
+		QCOMPARE(int(WireHops::fromString(QStringLiteral("diagonal"))), int(Mode::None));
+		QCOMPARE(int(WireHops::fromString(QString())), int(Mode::None));
+	}
+
+	void crossing_data()
+	{
+		QTest::addColumn<QVector<QPointF>>("wire");
+		QTest::addColumn<QVector<QPointF>>("other");
+		QTest::addColumn<int>("mode");
+		QTest::addColumn<QList<QPointF>>("expected");
+
+		const auto horizontal = line({0, 0}, {100, 0});
+		const auto vertical = line({50, -20}, {50, 20});
+		const int h = int(Mode::Horizontal), v = int(Mode::Vertical), none = int(Mode::None);
+
+		QTest::newRow("off") << horizontal << vertical << none << QList<QPointF>();
+		QTest::newRow("horizontal hops") << horizontal << vertical << h << QList<QPointF>{{50, 0}};
+		QTest::newRow("horizontal mode, vertical wire") << vertical << horizontal << h << QList<QPointF>();
+		QTest::newRow("vertical hops") << vertical << horizontal << v << QList<QPointF>{{50, 0}};
+		QTest::newRow("vertical mode, horizontal wire") << horizontal << vertical << v << QList<QPointF>();
+		QTest::newRow("reversed wire") << line({100, 0}, {0, 0}) << vertical << h << QList<QPointF>{{50, 0}};
+		QTest::newRow("T: other ends on the wire") << horizontal << line({50, 0}, {50, 20}) << h << QList<QPointF>();
+		QTest::newRow("T: other starts on the wire") << horizontal << line({50, -20}, {50, 0}) << h << QList<QPointF>();
+		QTest::newRow("too near the wire's end") << horizontal << line({2, -20}, {2, 20}) << h << QList<QPointF>();
+		QTest::newRow("parallel") << horizontal << line({0, 10}, {100, 10}) << h << QList<QPointF>();
+		QTest::newRow("misses") << horizontal << line({150, -20}, {150, 20}) << h << QList<QPointF>();
+		QTest::newRow("bent wire, second segment")
+				<< QVector<QPointF>{{0, -40}, {0, 0}, {100, 0}} << vertical << h << QList<QPointF>{{50, 0}};
+	}
+
+	void crossing()
+	{
+		QFETCH(QVector<QPointF>, wire);
+		QFETCH(QVector<QPointF>, other);
+		QFETCH(int, mode);
+		QFETCH(QList<QPointF>, expected);
+		QCOMPARE(WireHops::crossings(wire, {other}, Mode(mode)), expected);
+	}
+
+	void closeCrossings()
+	{
+		const auto wire = line({0, 0}, {100, 0});
+			// 6 apart: the arcs would overlap, so only the first hops
+		QCOMPARE(WireHops::crossings(wire, {line({40, -20}, {40, 20}), line({46, -20}, {46, 20})}, Mode::Horizontal),
+				 (QList<QPointF>{{40, 0}}));
+			// 10 apart, one grid step: both hop, in the wire's order
+		QCOMPARE(WireHops::crossings(wire, {line({60, -20}, {60, 20}), line({50, -20}, {50, 20})}, Mode::Horizontal),
+				 (QList<QPointF>{{50, 0}, {60, 0}}));
+	}
+
+	void pathWithoutHopsIsThePlainWire()
+	{
+		const QVector<QPointF> wire{{0, -40}, {0, 0}, {100, 0}};
+		QPainterPath plain;
+		plain.moveTo(wire.at(0));
+		plain.lineTo(wire.at(1));
+		plain.lineTo(wire.at(2));
+		QCOMPARE(WireHops::path(wire, {}, Mode::Horizontal), plain);
+		QCOMPARE(WireHops::path(wire, {{50, 0}}, Mode::None), plain);
+	}
+
+	void pathArcs_data()
+	{
+		QTest::addColumn<QVector<QPointF>>("wire");
+		QTest::addColumn<int>("mode");
+		QTest::addColumn<QRectF>("bounds");
+
+		const qreal r = WireHops::radius;
+			// The arc goes above a horizontal wire, right of a vertical one,
+			// whichever way the wire runs
+		QTest::newRow("left to right") << line({0, 0}, {100, 0}) << int(Mode::Horizontal)
+									   << QRectF(0, -r, 100, r);
+		QTest::newRow("right to left") << line({100, 0}, {0, 0}) << int(Mode::Horizontal)
+									   << QRectF(0, -r, 100, r);
+		QTest::newRow("top to bottom") << line({50, -20}, {50, 20}) << int(Mode::Vertical)
+									   << QRectF(50, -20, r, 40);
+		QTest::newRow("bottom to top") << line({50, 20}, {50, -20}) << int(Mode::Vertical)
+									   << QRectF(50, -20, r, 40);
+	}
+
+	void pathArcs()
+	{
+		QFETCH(QVector<QPointF>, wire);
+		QFETCH(int, mode);
+		QFETCH(QRectF, bounds);
+
+		const QPointF hop(50, 0);
+		const QPainterPath path = WireHops::path(wire, {hop}, Mode(mode));
+		const QRectF actual = path.boundingRect();
+		QVERIFY2(qAbs(actual.left() - bounds.left()) < 0.01 && qAbs(actual.top() - bounds.top()) < 0.01
+				 && qAbs(actual.right() - bounds.right()) < 0.01 && qAbs(actual.bottom() - bounds.bottom()) < 0.01,
+				 qPrintable(QStringLiteral("bounds %1,%2 %3x%4").arg(actual.x()).arg(actual.y())
+							.arg(actual.width()).arg(actual.height())));
+		QCOMPARE(path.pointAtPercent(0), wire.first());
+		QCOMPARE(path.pointAtPercent(1), wire.last());
+	}
+
+	void savedSettingSurvivesResave()
+	{
+		const QString fixture = QFINDTESTDATA("fixtures/wiring_list_arrows.qet");
+		QVERIFY2(!fixture.isEmpty(), "fixture project not found");
+
+			// The fixture has no setting: a resave must not add one
+		const QString plain = resave(fixture);
+		QVERIFY2(!plain.isEmpty(), "--resave failed");
+		QVERIFY(!plain.contains(QLatin1String("wire_crossings")));
+
+			// With the setting, a resave keeps it
+		QFile source(fixture);
+		QVERIFY(source.open(QIODevice::ReadOnly | QIODevice::Text));
+		QString text = QString::fromUtf8(source.readAll());
+		const int newdiagrams = text.indexOf(QLatin1String("<newdiagrams"));
+		QVERIFY(newdiagrams > 0);
+		text.insert(newdiagrams, QStringLiteral("<wire_crossings hop=\"vertical\"/>\n    "));
+		const QString with_setting = m_dir.filePath(QStringLiteral("with_setting.qet"));
+		QFile out(with_setting);
+		QVERIFY(out.open(QIODevice::WriteOnly | QIODevice::Text));
+		out.write(text.toUtf8());
+		out.close();
+
+		const QString saved = resave(with_setting);
+		QVERIFY2(!saved.isEmpty(), "--resave failed");
+		QVERIFY2(saved.contains(QLatin1String("<wire_crossings hop=\"vertical\"/>")),
+				 "the setting was lost on save");
+	}
+};
+
+QTEST_GUILESS_MAIN(tst_wirehops)
+
+#include "tst_wirehops.moc"