--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Framework/Scene2D/ZoomSceneTracker.cpp	Fri Apr 26 17:05:14 2019 +0200
@@ -0,0 +1,82 @@
+/**
+ * Stone of Orthanc
+ * Copyright (C) 2012-2016 Sebastien Jodogne, Medical Physics
+ * Department, University Hospital of Liege, Belgium
+ * Copyright (C) 2017-2019 Osimis S.A., Belgium
+ *
+ * This program is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Affero General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+
+#include "ZoomSceneTracker.h"
+
+namespace OrthancStone
+{
+  ZoomSceneTracker::ZoomSceneTracker(Scene2D& scene,
+                                     const PointerEvent& event,
+                                     unsigned int canvasWidth,
+                                     unsigned int canvasHeight) :
+    scene_(scene),
+    clickY_(event.GetMainPosition().GetY()),
+    aligner_(scene, event.GetMainPosition(), canvasWidth, canvasHeight),
+    originalSceneToCanvas_(scene.GetSceneToCanvasTransform())
+  {
+    if (canvasHeight <= 3)
+    {
+      active_ = false;
+    }
+    else
+    {
+      normalization_ = 1.0 / static_cast<double>(canvasHeight - 1);
+      active_ = true;
+    }
+  }
+  
+
+  void ZoomSceneTracker::Update(const PointerEvent& event)
+  {
+    static const double MIN_ZOOM = -4;
+    static const double MAX_ZOOM = 4;
+      
+    if (active_)
+    {
+      double y = event.GetMainPosition().GetY();
+      double dy = static_cast<double>(y - clickY_) * normalization_;  // In the range [-1,1]
+      double z;
+
+      // Linear interpolation from [-1, 1] to [MIN_ZOOM, MAX_ZOOM]
+      if (dy < -1.0)
+      {
+        z = MIN_ZOOM;
+      }
+      else if (dy > 1.0)
+      {
+        z = MAX_ZOOM;
+      }
+      else
+      {
+        z = MIN_ZOOM + (MAX_ZOOM - MIN_ZOOM) * (dy + 1.0) / 2.0;
+      }
+
+      double zoom = pow(2.0, z);
+
+      scene_.SetSceneToCanvasTransform(
+        AffineTransform2D::Combine(
+          AffineTransform2D::CreateScaling(zoom, zoom),
+          originalSceneToCanvas_));
+
+      aligner_.Apply();
+    }
+  }
+}