Примитивное перемещение линий

Если точнее, то перемещаем их концевые точки

Canvas.cpp

@@ -52,7 +52,15 @@ void Canvas::mousePressEvent(QMouseEvent* event)
 		qDebug() << "Scene point in" << scene.x() << scene.y();
 	#endif
 	
-	if (mode == Mode::DrawingLine) {
+	if (mode == Mode::None){
+		Point* p = findPointAt(scene);
+		if (p) {
+			draggedPoint = p;
+			dragOffset = scene - QPointF(*p->x, *p->y);
+			return;
+		}
+	}
+	else if (mode == Mode::DrawingLine) {
 		if (!current_line) {
 			current_line = new Line();
 			current_line->set_tag(obj_count);
@@ -101,6 +109,7 @@ void Canvas::mousePressEvent(QMouseEvent* event)
 			current_line = nullptr;
 			mode = Mode::None;
 			obj_count++;
+			after_constraint = true;
 		}
 			update();
 			return;
@@ -133,6 +142,7 @@ void Canvas::mousePressEvent(QMouseEvent* event)
 			current_line = nullptr;
 			update();
 			mode = Mode::None;
+			after_constraint = true;
 		}
 		else {
 			
@@ -189,11 +199,30 @@ void Canvas::mousePressEvent(QMouseEvent* event)
 		sys.addConstraintP2PCoincident(*firstPoint, *clickedPoint, constraints_count++);
 		firstPoint = nullptr;
 		mode = Mode::None;
+		after_constraint = true;
 		update();
 		return;
 	}
 }
 
+void Canvas::mouseMoveEvent(QMouseEvent* event)
+{
+	if (draggedPoint) {
+		QPointF pos = event->pos() - dragOffset;
+		*draggedPoint->x = pos.x();
+		*draggedPoint->y = pos.y();
+		update();
+	}
+}
+
+void Canvas::mouseReleaseEvent(QMouseEvent* event)
+{
+	if (draggedPoint) {
+		draggedPoint = nullptr;
+		update();
+	}
+}
+
 void Canvas::paintEvent(QPaintEvent*)
 {
 	QPainter p(this);
@@ -205,10 +234,12 @@ void Canvas::paintEvent(QPaintEvent*)
 		if (res == SolveStatus::Success || res == SolveStatus::Converged) {
 			sys.applySolution();
 		}
-		else {
+		else if (res == SolveStatus::Failed && after_constraint){
+			QMessageBox::warning(this, QString("Error!"), QString("Last constraint is unavailable!"));
 			sys.removeConstraint(sys.get_last_constraint());
 			constraints_count--;
 		}
+		after_constraint = false;
 	}
 
 	for (Line* line : lines) {

Canvas.h

@@ -41,6 +41,8 @@ public:
 
 protected:
     void mousePressEvent(QMouseEvent* event) override;
+    void mouseMoveEvent(QMouseEvent* event) override;
+    void mouseReleaseEvent(QMouseEvent* event) override;
     void paintEvent(QPaintEvent* event) override;
 
 private:
@@ -52,6 +54,10 @@ private:
     LinePair makeOrderedPair(Line* l1, Line* l2);
     bool areAlreadyParallel(Line* l1, Line* l2);           // проверка на дубликат
 
+    // ====================== Перемещение ======================
+    Point* draggedPoint{ nullptr };
+    QPointF dragOffset;
+
     // ====================== Данные сцены ======================
     System               sys;                     // геометрический солвер
     QVector<Line*>       lines;                   // завершённые линии
@@ -63,6 +69,7 @@ private:
     Line* current_line{ nullptr };
     Point* firstPoint{ nullptr };
     Mode mode{ Mode::None };
+    bool after_constraint{ false };
 
     int obj_count{ 0 };            // тег для новых объектов
     int constraints_count{ 0 };    // тег для новых ограничений