Added implementation of level of details per layer and item type pairs basis...

Added implementation of level of details per layer and item type pairs basis (items on every layer have a possibility to define the minimum VIEW scale to be shown).

common/view/view.cpp

@@ -459,7 +459,8 @@ struct VIEW::drawItem
             // Draw using cached information or create one
             int group = aItem->getGroup( currentLayer->id );
 
-            if( group >= 0 && aItem->ViewIsVisible() )
+            if( group >= 0 && aItem->ViewIsVisible() &&
+                aItem->ViewGetLOD( currentLayer->id ) < view->m_scale )
             {
                 gal->DrawGroup( group );
             }
@@ -471,7 +472,8 @@ struct VIEW::drawItem
                 gal->EndGroup();
             }
         }
-        else if( aItem->ViewIsVisible() )
+        else if( aItem->ViewIsVisible() &&
+                 aItem->ViewGetLOD( currentLayer->id ) < view->m_scale )
         {
             // Immediate mode
             view->m_painter->Draw( aItem, currentLayer->id );

include/view/view_item.h

@@ -227,6 +227,17 @@ public:
         return m_viewVisible;
     }
 
+    /**
+     * Function ViewGetLOD()
+     * Returns the level of detail of the item. A level of detail is the minimal VIEW scale that
+     * is sufficient for an item to be shown on a given layer.
+     */
+    virtual unsigned int ViewGetLOD( int aLayer ) const
+    {
+        // By default always show the item
+        return 0;
+    }
+
     /**
      * Function ViewUpdate()
      * For dynamic VIEWs, informs the associated VIEW that the graphical representation of