Fixed issue #532. Unexpected error occurs when zoom out image.

(grafted from c9e825b2ba62707e063700cea95ded566f158d6a)

--HG--
branch : develop

src/libs/vwidgets/vmaingraphicsview.cpp

@@ -57,6 +57,9 @@ class QWheelEvent;
 const int GraphicsViewZoom::duration = 300;
 const int GraphicsViewZoom::updateInterval = 40;
 
+const qreal maxScale = 50.0;  // for zoom in
+const qreal minScale = 0.004; // for zoom out
+
 //---------------------------------------------------------------------------------------------------------------------
 GraphicsViewZoom::GraphicsViewZoom(QGraphicsView* view)
   : QObject(view),
@@ -85,12 +88,18 @@ GraphicsViewZoom::GraphicsViewZoom(QGraphicsView* view)
 //---------------------------------------------------------------------------------------------------------------------
 void GraphicsViewZoom::gentle_zoom(double factor)
 {
+    // We need to check current scale factor because in Windows we have an error when we zoom in or zoom out to much.
+    // See issue #532: Unexpected error occurs when zoom out image.
+    // factor > 1 for zoomIn and factor < 1 for zoomOut.
+    if ((_view->transform().m11() < maxScale && factor > 1) ||
+        (_view->transform().m11() > minScale && factor < 1))
+    {
         _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.
+            // boundaries don't allow to put any picture point at any viewport position we will provide fictive scene
-      // Temporary and bigger than view, scene size will help position an image under cursor.
+            // size. Temporary and bigger than view, scene size will help position an image under cursor.
             FictiveSceneRect(_view->scene(), _view);
         }
         _view->centerOn(target_scene_pos);
@@ -101,6 +110,7 @@ void GraphicsViewZoom::gentle_zoom(double factor)
         // In the end we just set correct scene size
         VMainGraphicsView::NewSceneRect(_view->scene(), _view);
         emit zoomed();
+    }
 }
 
 //---------------------------------------------------------------------------------------------------------------------
@@ -348,17 +358,27 @@ VMainGraphicsView::VMainGraphicsView(QWidget *parent)
 //---------------------------------------------------------------------------------------------------------------------
 void VMainGraphicsView::ZoomIn()
 {
+    // We need to check current scale factor because in Windows we have an error when we zoom in or zoom out to much.
+    // See issue #532: Unexpected error occurs when zoom out image.
+    if (this->transform().m11() < maxScale)
+    {
         scale(1.1, 1.1);
         VMainGraphicsView::NewSceneRect(this->scene(), this);
         emit NewFactor(1.1);
+    }
 }
 
 //---------------------------------------------------------------------------------------------------------------------
 void VMainGraphicsView::ZoomOut()
 {
+    // We need to check current scale factor because in Windows we have an error when we zoom in or zoom out to much.
+    // See issue #532: Unexpected error occurs when zoom out image.
+    if (this->transform().m11() > minScale)
+    {
         scale(1.0/1.1, 1.0/1.1);
         VMainGraphicsView::NewSceneRect(this->scene(), this);
         emit NewFactor(1.0/1.1);
+    }
 }
 
 //---------------------------------------------------------------------------------------------------------------------