CelView: Add dragging for mouse

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

source/celview.cpp

@@ -20,8 +20,23 @@ CelScene::CelScene(QWidget *v)
 {
 }
 
+void CelScene::keyPressEvent(QKeyEvent *keyEvent)
+{
+    if (keyEvent->modifiers() & Qt::ShiftModifier)
+        static_cast<CelView *>(view)->setDragMode(QGraphicsView::ScrollHandDrag);
+}
+
+void CelScene::keyReleaseEvent(QKeyEvent *keyEvent)
+{
+    static_cast<CelView *>(view)->setDragMode(QGraphicsView::NoDrag);
+}
+
 void CelScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
+    // bail out if dragging mode on mouse is enabled
+    if (static_cast<CelView *>(view)->dragMode() == QGraphicsView::ScrollHandDrag)
+        return;
+
     if (event->button() != Qt::LeftButton) {
         return;
     }
@@ -520,3 +535,13 @@ void CelView::dropEvent(QDropEvent *event)
     // try to insert as frames
     ((MainWindow *)this->window())->openImageFiles(IMAGE_FILE_MODE::AUTO, filePaths, false);
 }
+
+void CelView::setDragMode(enum QGraphicsView::DragMode dragMode)
+{
+    this->ui->celGraphicsView->setDragMode(dragMode);
+}
+
+QGraphicsView::DragMode CelView::dragMode()
+{
+    return this->ui->celGraphicsView->dragMode();
+}

source/celview.h

@@ -6,6 +6,7 @@
 #include <QGraphicsScene>
 #include <QGraphicsSceneDragDropEvent>
 #include <QGraphicsSceneMouseEvent>
+#include <QGraphicsView>
 #include <QPoint>
 #include <QStringList>
 #include <QTimer>
@@ -28,6 +29,8 @@ class CelScene : public QGraphicsScene {
     CelScene(QWidget *view);
 
 private slots:
+    void keyPressEvent(QKeyEvent *keyEvent);
+    void keyReleaseEvent(QKeyEvent *keyEvent);
     void mousePressEvent(QGraphicsSceneMouseEvent *event);
     void dragEnterEvent(QGraphicsSceneDragDropEvent *event);
     void dragMoveEvent(QGraphicsSceneDragDropEvent *event);
@@ -56,6 +59,8 @@ class CelView : public QWidget {
     void replaceCurrentFrame(const QString &imagefilePath);
     void removeCurrentFrame();
     void regroupFrames(int numGroups);
+    void setDragMode(enum QGraphicsView::DragMode dragMode);
+    QGraphicsView::DragMode dragMode();
 
     void displayFrame();