QGraphicsView Zooming in and out under mouse position using mouse wheel finally

works like i want.

--HG--
branch : develop

src/libs/vwidgets/vmaingraphicsview.cpp

@@ -55,11 +55,20 @@ GraphicsViewZoom::GraphicsViewZoom(QGraphicsView* view)
 void GraphicsViewZoom::gentle_zoom(double factor)
 {
   _view->scale(factor, factor);
+  if (factor < 1)
+  {
+      // Because QGraphicsView centers the picture when it's smaller than the view. And QGraphicsView's scrolls
+      // boundaries don't allow to put any picture point at any viewport position we will provide fictive scene size.
+      // Temporary and bigger than view, scene size will help position an image under cursor.
+      FictiveSceneRect(_view->scene(), _view);
+  }
   _view->centerOn(target_scene_pos);
   QPointF delta_viewport_pos = target_viewport_pos - QPointF(_view->viewport()->width() / 2.0,
                                                              _view->viewport()->height() / 2.0);
   QPointF viewport_center = _view->mapFromScene(target_scene_pos) - delta_viewport_pos;
   _view->centerOn(_view->mapToScene(viewport_center.toPoint()));
+  // In the end we just set correct scene size
+  VMainGraphicsView::NewSceneRect(_view->scene(), _view);
   emit zoomed();
 }
 
@@ -112,8 +121,8 @@ void GraphicsViewZoom::animFinished()
      * If don't do that we will zoom using old value cursor position on scene. It is not what we expect.
      * Almoust the same we do in method GraphicsViewZoom::eventFilter.
      */
-    QPoint pos = _view->mapFromGlobal(QCursor::pos());
-    QPointF delta = target_scene_pos - _view->mapToScene(pos);
+    const QPoint pos = _view->mapFromGlobal(QCursor::pos());
+    const QPointF delta = target_scene_pos - _view->mapToScene(pos);
     if (qAbs(delta.x()) > 5 || qAbs(delta.y()) > 5)
     {
         target_viewport_pos = pos;
@@ -173,6 +182,39 @@ bool GraphicsViewZoom::eventFilter(QObject *object, QEvent *event)
   return false;
 }
 
+//---------------------------------------------------------------------------------------------------------------------
+void GraphicsViewZoom::FictiveSceneRect(QGraphicsScene *sc, QGraphicsView *view)
+{
+    SCASSERT(sc != nullptr);
+    SCASSERT(view != nullptr);
+
+    //Calculate view rect
+    //to receive the currently visible area, map the widgets bounds to the scene
+    const QPointF a = view->mapToScene(0, 0 );
+    const QPointF b = view->mapToScene(view->viewport()->width(), view->viewport()->height());
+    QRectF viewRect = QRectF( a, b );
+
+    //Calculate scene rect
+    const QRectF sceneRect = sc->sceneRect();
+
+    if (not sceneRect.contains(viewRect))
+    {//Scene less than view
+        //Scale view
+        QLineF topLeftRay(viewRect.center(), viewRect.topLeft());
+        topLeftRay.setLength(topLeftRay.length()*2);
+
+        QLineF bottomRightRay(viewRect.center(), viewRect.bottomRight());
+        bottomRightRay.setLength(bottomRightRay.length()*2);
+
+        viewRect = QRectF(topLeftRay.p2(), bottomRightRay.p2());
+
+        //Unite two rects
+        const QRectF newRect = sceneRect.united(viewRect);
+
+        sc->setSceneRect(newRect);
+    }
+}
+
 //---------------------------------------------------------------------------------------------------------------------
 /**
  * @brief VMainGraphicsView constructor.

src/libs/vwidgets/vmaingraphicsview.h

@@ -36,11 +36,6 @@
  * This class adds ability to zoom QGraphicsView using mouse wheel. The point under cursor
  * remains motionless while it's possible.
  *
- * Note that it becomes not possible when the scene's
- * size is not large enough comparing to the viewport size. QGraphicsView centers the picture
- * when it's smaller than the view. And QGraphicsView's scrolls boundaries don't allow to
- * put any picture point at any viewport position.
- *
  * When the user starts scrolling, this class remembers original scene position and
  * keeps it until scrolling is completed. It's better than getting original scene position at
  * each scrolling step because that approach leads to position errors due to before-mentioned
@@ -79,18 +74,18 @@ public slots:
     void scrollingTime(qreal x);
     void animFinished();
 private:
+    Q_DISABLE_COPY(GraphicsViewZoom)
     QGraphicsView*        _view;
     Qt::KeyboardModifiers _modifiers;
     double                _zoom_factor_base;
     QPointF               target_scene_pos;
     QPointF               target_viewport_pos;
     QTimeLine            *anim;
-
-    bool eventFilter(QObject* object, QEvent* event);
-private:
-    Q_DISABLE_COPY(GraphicsViewZoom)
     /** @brief _numScheduledScalings keep number scheduled scalings. */
     qint32   _numScheduledScalings;
+
+    virtual bool eventFilter(QObject* object, QEvent* event) Q_DECL_OVERRIDE;
+    void FictiveSceneRect(QGraphicsScene *sc, QGraphicsView *view);
 };
 
 /**