[layouts] Middle mouse click in pan tool should recenter view

Port missing functionality from composer

src/gui/layout/qgslayoutviewtoolpan.cpp

@@ -26,6 +26,8 @@ QgsLayoutViewToolPan::QgsLayoutViewToolPan( QgsLayoutView *view )
 
 void QgsLayoutViewToolPan::layoutPressEvent( QgsLayoutViewMouseEvent *event )
 {
+  mMousePressStartPos = event->pos();
+
   if ( event->button() != Qt::LeftButton )
   {
     event->ignore();
@@ -53,8 +55,30 @@ void QgsLayoutViewToolPan::layoutMoveEvent( QgsLayoutViewMouseEvent *event )
 
 void QgsLayoutViewToolPan::layoutReleaseEvent( QgsLayoutViewMouseEvent *event )
 {
+  bool clickOnly = !isClickAndDrag( mMousePressStartPos, event->pos() );
+
+  if ( event->button() == Qt::MiddleButton && clickOnly )
+  {
+    //middle mouse button click = recenter on point
+
+    //get current visible part of scene
+    QRect viewportRect( 0, 0, view()->viewport()->width(), view()->viewport()->height() );
+    QgsRectangle visibleRect = QgsRectangle( view()->mapToScene( viewportRect ).boundingRect() );
+    QPointF scenePoint = event->layoutPoint();
+    visibleRect.scale( 1, scenePoint.x(), scenePoint.y() );
+    QRectF boundsRect = visibleRect.toRectF();
+
+    //zoom view to fit desired bounds
+    view()->fitInView( boundsRect, Qt::KeepAspectRatio );
+    view()->emitZoomLevelChanged();
+    view()->viewChanged();
+    return;
+  }
+
   if ( !mIsPanning || event->button() != Qt::LeftButton )
   {
+    view()->emitZoomLevelChanged();
+    view()->viewChanged();
     event->ignore();
     return;
   }

src/gui/layout/qgslayoutviewtoolpan.h

@@ -46,6 +46,8 @@ class GUI_EXPORT QgsLayoutViewToolPan : public QgsLayoutViewTool
 
     bool mIsPanning = false;
     QPoint mLastMousePos;
+    //! Start position for mouse press
+    QPoint mMousePressStartPos;
 
 };