View: Add dragging for mouse

This patch adds dragging for mouse, so by pressing middle mouse button
dragging mode is being changed to scroll hand drag, basically it allows
to navigate on the image without pressing scroll bars.

To do that, View class had to be introduced which has been introduced to
override some of QGraphicsView mouse events and to promote QGraphicsView
widget to it.

CMakeLists.txt

@@ -12,6 +12,8 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Widgets)
 find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Widgets)
 
+
+include_directories(source/)
 set(PROJECT_SOURCES
         source/celview.cpp
         source/celview.h
@@ -49,6 +51,8 @@ set(PROJECT_SOURCES
         source/exportdialog.cpp
         source/exportdialog.h
         source/exportdialog.ui
+        source/view.cpp
+        source/view.h
         source/levelcelview.cpp
         source/levelcelview.h
         source/levelcelview.ui

source/celview.cpp

@@ -22,6 +22,10 @@ CelScene::CelScene(QWidget *v)
 
 void CelScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
+    // return if currently set drag mode is scroll hand drag
+    if (views()[0]->dragMode() == QGraphicsView::ScrollHandDrag)
+        return;
+
     if (event->button() != Qt::LeftButton) {
         return;
     }

source/view.cpp

@@ -0,0 +1,45 @@
+#include "view.h"
+
+View::View(QWidget *parent)
+    : QGraphicsView(parent)
+{
+}
+
+void View::mousePressEvent(QMouseEvent *event)
+{
+    switch (event->button()) {
+    case Qt::LeftButton: {
+        QGraphicsView::mousePressEvent(event);
+        break;
+    }
+    case Qt::MiddleButton: {
+        this->setDragMode(QGraphicsView::ScrollHandDrag);
+
+        // after middle button has been pressed - send the mouse press event to base
+        // class that holds this scene, since it will toggle on dragging on ScrollHandDrag
+        QMouseEvent *pressEvent = new QMouseEvent(QEvent::MouseButtonPress,
+            event->pos(), event->globalPosition(), Qt::MouseButton::LeftButton,
+            Qt::MouseButton::LeftButton, Qt::KeyboardModifier::NoModifier);
+
+        QGraphicsView::mousePressEvent(pressEvent);
+        break;
+    }
+    default: {
+        QGraphicsView::mousePressEvent(event);
+        break;
+    }
+    }
+}
+
+void View::mouseReleaseEvent(QMouseEvent *event)
+{
+    switch (event->button()) {
+    case Qt::LeftButton: {
+        break;
+    }
+    case Qt::MiddleButton: {
+        this->setDragMode(QGraphicsView::NoDrag);
+        break;
+    }
+    }
+}

source/view.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <QGraphicsView>
+#include <QMouseEvent>
+#include <QObject>
+
+class View : public QGraphicsView {
+    Q_OBJECT
+
+public:
+    View(QWidget *parent = nullptr);
+
+private slots:
+    void mouseReleaseEvent(QMouseEvent *event);
+    void mousePressEvent(QMouseEvent *event);
+};