diff --git a/GraphicsView/include/CGAL/Qt/qglviewer.h b/GraphicsView/include/CGAL/Qt/qglviewer.h
index 17b91c38b45..ccf4e26e378 100644
--- a/GraphicsView/include/CGAL/Qt/qglviewer.h
+++ b/GraphicsView/include/CGAL/Qt/qglviewer.h
@@ -1205,6 +1205,7 @@ protected:
   qglviewer::Vec _offset;
   //C o n t e x t
   bool is_ogl_4_3;
+  bool is_sharing;
 public:
   //! Is used to know if the openGL context is 4.3 or ES 2.0.
   //! @returns `true` if the context is 4.3.
diff --git a/Polyhedron/demo/Polyhedron/CMakeLists.txt b/Polyhedron/demo/Polyhedron/CMakeLists.txt
index 4e949955731..52067f57ef0 100644
--- a/Polyhedron/demo/Polyhedron/CMakeLists.txt
+++ b/Polyhedron/demo/Polyhedron/CMakeLists.txt
@@ -129,6 +129,7 @@ if(CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND )
   find_package(Boost COMPONENTS thread system filesystem)
 
   qt5_wrap_ui( MainWindowUI_files MainWindow.ui)
+  qt5_wrap_ui( SubViewerUI_files SubViewer.ui)
   qt5_wrap_ui( statisticsUI_FILES Statistics_on_item_dialog.ui)
   qt5_wrap_ui( FileLoaderDialogUI_files FileLoaderDialog.ui )
   qt5_wrap_ui( Show_point_dialogUI_FILES Show_point_dialog.ui )
@@ -309,7 +310,8 @@ if(CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND )
     Polyhedron_demo.cpp
     File_loader_dialog_moc.cpp
     ${CGAL_Qt5_RESOURCE_FILES} ${CGAL_Qt5_MOC_FILES}
-    ${FileLoaderDialogUI_files} ${MainWindowUI_files} ${PreferencesUI_FILES} ${statisticsUI_FILES})
+    ${FileLoaderDialogUI_files} ${MainWindowUI_files} ${PreferencesUI_FILES} 
+    ${statisticsUI_FILES} ${SubViewerUI_files})
   target_link_libraries(polyhedron_demo PUBLIC
     demo_framework point_dialog Qt5::Gui Qt5::OpenGL Qt5::Widgets Qt5::Script)
   add_executable  ( Polyhedron_3 Polyhedron_3.cpp )
diff --git a/Polyhedron/demo/Polyhedron/MainWindow.cpp b/Polyhedron/demo/Polyhedron/MainWindow.cpp
index c80a8690b1e..af57cde27d0 100644
--- a/Polyhedron/demo/Polyhedron/MainWindow.cpp
+++ b/Polyhedron/demo/Polyhedron/MainWindow.cpp
@@ -51,6 +51,7 @@
 #include <CGAL/Three/Polyhedron_demo_plugin_interface.h>
 #include <CGAL/Three/Polyhedron_demo_io_plugin_interface.h>
 #include <CGAL/Three/Scene_item_with_properties.h>
+#include "ui_SubViewer.h"
 #include "ui_MainWindow.h"
 #include "ui_Preferences.h"
 #include "ui_Statistics_on_item_dialog.h"
@@ -147,6 +148,7 @@ MainWindow::MainWindow(bool verbose, QWidget* parent)
   // Save some pointers from ui, for latter use.
   sceneView = ui->sceneView;
   viewer = ui->viewer;
+  viewer->setObjectName("viewer");
   // do not save the state of the viewer (anoying)
   viewer->setStateFileName(QString::null);
 
@@ -167,6 +169,12 @@ MainWindow::MainWindow(bool verbose, QWidget* parent)
     connect(shortcut, SIGNAL(activated()),
             this, SLOT(toggleFullScreen()));
   }
+  setupViewer(viewer, 0);
+  
+  viewer->setKeyDescription(Qt::Key_R + Qt::CTRL,
+                      tr("Recenters the viewer under the cursor. "
+                         "If the cursor is not over any viewer, "
+                         "then all viewers are recentered."));
 
   proxyModel = new QSortFilterProxyModel(this);
   proxyModel->setSourceModel(scene);
@@ -206,7 +214,7 @@ MainWindow::MainWindow(bool verbose, QWidget* parent)
           this, SLOT(removeManipulatedFrame(CGAL::Three::Scene_item*)));
 
   connect(scene, SIGNAL(updated_bbox(bool)),
-          this, SLOT(updateViewerBBox(bool)));
+          this, SLOT(updateViewersBboxes(bool)));
 
   connect(scene, SIGNAL(selectionChanged(int)),
           this, SLOT(selectSceneItem(int)));
@@ -806,7 +814,7 @@ void MainWindow::viewerShow(float xmin,
     min_(xmin, ymin, zmin),
     max_(xmax, ymax, zmax);
 
-  if(min_ == max_) return viewerShow(xmin, ymin, zmin);
+  if(min_ == max_) return viewerShow(viewer, xmin, ymin, zmin);
 
   viewer->camera()->setPivotPoint((min_+max_)*0.5);
 
@@ -818,18 +826,17 @@ void MainWindow::viewerShow(float xmin,
   viewer->setVisualHintsMask(1);
 }
 
-void MainWindow::viewerShow(float x, float y, float z) {
-  // viewer->camera()->lookAt(CGAL::qglviewer::Vec(x, y, z));
+void MainWindow::viewerShow(Viewer_interface* vi, float x, float y, float z) {
+  
+  CGAL::qglviewer::ManipulatedCameraFrame backup_frame(*vi->camera()->frame());
+  vi->camera()->fitSphere(CGAL::qglviewer::Vec(x, y, z),
+                              vi->camera()->sceneRadius()/100);
+  CGAL::qglviewer::ManipulatedCameraFrame new_frame(*vi->camera()->frame());
+  *vi->camera()->frame() = backup_frame;
+  vi->camera()->interpolateTo(new_frame, 1.f);
+  vi->setVisualHintsMask(1);
 
-  CGAL::qglviewer::ManipulatedCameraFrame backup_frame(*viewer->camera()->frame());
-  viewer->camera()->fitSphere(CGAL::qglviewer::Vec(x, y, z),
-                              viewer->camera()->sceneRadius()/100);
-  CGAL::qglviewer::ManipulatedCameraFrame new_frame(*viewer->camera()->frame());
-  *viewer->camera()->frame() = backup_frame;
-  viewer->camera()->interpolateTo(new_frame, 1.f);
-  viewer->setVisualHintsMask(1);
-
-  viewer->camera()->setPivotPoint(CGAL::qglviewer::Vec(x, y, z));
+  vi->camera()->setPivotPoint(CGAL::qglviewer::Vec(x, y, z));
 }
 
 void MainWindow::message(QString message, QString colorName, QString font) {
@@ -860,10 +867,24 @@ void MainWindow::error(QString text) {
   this->message("ERROR: " + text, "red");
 }
 
-void MainWindow::updateViewerBBox(bool recenter = true)
+void MainWindow::updateViewersBboxes(bool recenter)
 {
-  const Scene::Bbox bbox = scene->bbox();
-    CGAL::qglviewer::Vec center = viewer->camera()->pivotPoint();
+  CGAL::qglviewer::Vec min, max;
+  computeViewerBBox(min, max);
+  Q_FOREACH(CGAL::QGLViewer* v, CGAL::QGLViewer::QGLViewerPool())
+  {
+    if(v == NULL)
+      continue;
+    Viewer* vi = static_cast<Viewer*>(v);
+    updateViewerBbox(vi, recenter, min, max);
+  }
+
+}
+
+void MainWindow::computeViewerBBox(CGAL::qglviewer::Vec& min, CGAL::qglviewer::Vec& max)
+{
+  const Scene::Bbox bbox = scene->visibleBbox();
+  const Scene::Bbox all_bbox = scene->bbox();
   const double xmin = bbox.xmin();
   const double ymin = bbox.ymin();
   const double zmin = bbox.zmin();
@@ -871,15 +892,26 @@ void MainWindow::updateViewerBBox(bool recenter = true)
   const double ymax = bbox.ymax();
   const double zmax = bbox.zmax();
 
+  const double axmin = all_bbox.xmin();
+  const double aymin = all_bbox.ymin();
+  const double azmin = all_bbox.zmin();
+  const double axmax = all_bbox.xmax();
+  const double aymax = all_bbox.ymax();
+  const double azmax = all_bbox.zmax();
+
+
+
+  min = CGAL::qglviewer::Vec(xmin, ymin, zmin);
+  max= CGAL::qglviewer::Vec(xmax, ymax, zmax);
+
+  CGAL::qglviewer::Vec abbox_center((axmin+axmax)/2, (aymin+aymax)/2, (azmin+azmax)/2),
+      bbox_center((xmin+xmax)/2, (ymin+ymax)/2, (zmin+zmax)/2);
 
-  CGAL::qglviewer::Vec
-    vec_min(xmin, ymin, zmin),
-    vec_max(xmax, ymax, zmax),
-    bbox_center((xmin+xmax)/2, (ymin+ymax)/2, (zmin+zmax)/2);
   CGAL::qglviewer::Vec offset(0,0,0);
+
   double l_dist = (std::max)((std::abs)(bbox_center.x - viewer->offset().x),
-                      (std::max)((std::abs)(bbox_center.y - viewer->offset().y),
-                          (std::abs)(bbox_center.z - viewer->offset().z)));
+                             (std::max)((std::abs)(bbox_center.y - viewer->offset().y),
+                                        (std::abs)(bbox_center.z - viewer->offset().z)));
   if((std::log2)(l_dist) > 13.0 )
     for(int i=0; i<3; ++i)
     {
@@ -888,25 +920,20 @@ void MainWindow::updateViewerBBox(bool recenter = true)
     }
   if(offset != viewer->offset())
   {
-    viewer->setOffset(offset);
+    Q_FOREACH(CGAL::QGLViewer* v, CGAL::QGLViewer::QGLViewerPool())
+    {
+      if(v == NULL)
+        continue;
+      Viewer* vi = qobject_cast<Viewer*>(v);
+      vi->setOffset(offset);
+    }
     for(int i=0; i<scene->numberOfEntries(); ++i)
     {
+//      scene->item(i)->invalidate(Scene_item::GEOMETRY);
       scene->item(i)->invalidateOpenGLBuffers();
       scene->item(i)->itemChanged();
     }
   }
-
-
-  viewer->setSceneBoundingBox(vec_min,
-                              vec_max);
-  if(recenter)
-  {
-    viewer->camera()->showEntireScene();
-  }
-  else
-  {
-    viewer->camera()->setPivotPoint(center);
-  }
 }
 
 void MainWindow::reloadItem() {
@@ -1238,31 +1265,36 @@ void MainWindow::selectionChanged()
   scene->setSelectedItemIndex(getSelectedSceneItemIndex());
   scene->setSelectedItemsList(getSelectedSceneItemIndices());
   CGAL::Three::Scene_item* item = scene->item(getSelectedSceneItemIndex());
-  if(item != NULL && item->manipulatable()) {
-    viewer->setManipulatedFrame(item->manipulatedFrame());
-  } else {
-    viewer->setManipulatedFrame(0);
-  }
-  if(viewer->manipulatedFrame() == 0) {
-    Q_FOREACH(CGAL::Three::Scene_item* item, scene->entries()) {
-      if(item->manipulatable() && item->manipulatedFrame() != 0) {
-        if(viewer->manipulatedFrame() != 0) {
-          // there are at least two possible frames
-          viewer->setManipulatedFrame(0);
-          break;
-        } else {
-          viewer->setManipulatedFrame(item->manipulatedFrame());
+  Q_FOREACH(CGAL::QGLViewer* vi, CGAL::QGLViewer::QGLViewerPool())
+  {
+    if(vi == NULL)
+      continue;
+    
+    if(item != NULL && item->manipulatable()) {
+      vi->setManipulatedFrame(item->manipulatedFrame());
+    } else {
+      vi->setManipulatedFrame(0);
+    }
+    if(vi->manipulatedFrame() == 0) {
+      Q_FOREACH(CGAL::Three::Scene_item* item, scene->entries()) {
+        if(item->manipulatable() && item->manipulatedFrame() != 0) {
+          if(vi->manipulatedFrame() != 0) {
+            // there are at least two possible frames
+            vi->setManipulatedFrame(0);
+            break;
+          } else {
+            vi->setManipulatedFrame(item->manipulatedFrame());
+          }
         }
       }
     }
+    if(vi->manipulatedFrame() != 0) {
+      connect(vi->manipulatedFrame(), SIGNAL(modified()),
+              this, SLOT(updateInfo()));
+    }
+    vi->update();
   }
-  if(viewer->manipulatedFrame() != 0) {
-    connect(viewer->manipulatedFrame(), SIGNAL(modified()),
-            this, SLOT(updateInfo()));
-  }
-  viewer->update();
 }
-
 void MainWindow::contextMenuRequested(const QPoint& global_pos) {
   int index = scene->mainSelectionIndex();
   showSceneContextMenu(index, global_pos);
@@ -1958,10 +1990,16 @@ void MainWindow::on_actionPreferences_triggered()
 void MainWindow::setBackgroundColor()
 {
   QColor c =  QColorDialog::getColor();
-  if(c.isValid()) {
-    viewer->setBackgroundColor(c);
-    viewer->update();
-  }
+   if(c.isValid()) {
+     Q_FOREACH(CGAL::QGLViewer* v, CGAL::QGLViewer::QGLViewerPool())
+     {
+       if(v == NULL)
+         continue;
+       v->setBackgroundColor(c);
+       v->update();
+     }
+   }
+  
 }
 
 void MainWindow::setLighting_triggered()
@@ -1977,7 +2015,8 @@ void MainWindow::on_actionLookAt_triggered()
   if( i == QDialog::Accepted &&
       dialog.has_correct_coordinates() )
   {
-    viewerShow((float)dialog.get_x()+viewer->offset().x,
+    viewerShow(viewer, 
+               (float)dialog.get_x()+viewer->offset().x,
                (float)dialog.get_y()+viewer->offset().y,
                (float)dialog.get_z()+viewer->offset().z);
   }
@@ -1999,7 +2038,7 @@ void MainWindow::viewerShowObject()
                max.x, max.y, max.z);
   }
 }
-
+/* to check
 QString MainWindow::cameraString() const
 {
   const CGAL::qglviewer::Vec pos = viewer->camera()->position() - viewer->offset();
@@ -2013,21 +2052,26 @@ QString MainWindow::cameraString() const
     .arg(q[1])
     .arg(q[2])
     .arg(q[3]);
+}*/
+QString MainWindow::cameraString(CGAL::Three::Viewer_interface* v) const
+{
+  return v->dumpCameraCoordinates();
 }
 
 void MainWindow::on_actionDumpCamera_triggered()
 {
   //remove offset
   information(QString("Camera: %1")
-              .arg(cameraString()));
+              .arg(cameraString(viewer)));
 }
 
 void MainWindow::on_actionCopyCamera_triggered()
 {
   //remove offset
-  qApp->clipboard()->setText(this->cameraString());
+  qApp->clipboard()->setText(this->cameraString(viewer));
 }
 
+/* to check
 void MainWindow::on_actionPasteCamera_triggered()
 {
   //add offset
@@ -2044,6 +2088,11 @@ void MainWindow::on_actionPasteCamera_triggered()
   for(int i=0; i<7; ++i)
     s.append(new_s[i]).append(" ");
   viewer->moveCameraToCoordinates(s, 0.5f);
+}*/
+void MainWindow::on_actionPasteCamera_triggered()
+{
+  QString s = qApp->clipboard()->text();
+  viewer->moveCameraToCoordinates(s, 0.5f);
 }
 
 void MainWindow::setAddKeyFrameKeyboardModifiers(::Qt::KeyboardModifiers m)
@@ -2053,8 +2102,17 @@ void MainWindow::setAddKeyFrameKeyboardModifiers(::Qt::KeyboardModifiers m)
 
 void MainWindow::on_actionRecenterScene_triggered()
 {
-  updateViewerBBox();
-  viewer->camera()->interpolateToFitScene();
+  scene->computeBbox();
+  scene->computeVisibleBbox();
+  CGAL::qglviewer::Vec min, max;
+  computeViewerBBox(min, max);
+  Q_FOREACH(CGAL::QGLViewer* v, CGAL::QGLViewer::QGLViewerPool())
+  {
+    if(v == NULL)
+      continue;
+    updateViewerBbox(static_cast<Viewer*>(v), true, min, max);
+    v->camera()->interpolateToFitScene();
+  }
 }
 
 void MainWindow::on_actionLoadPlugin_triggered()
@@ -2368,6 +2426,7 @@ void MainWindow::propagate_action()
     }
   }
 }
+
 void MainWindow::setTransparencyPasses(int val)
 {
   viewer->setTotalPass(val);
@@ -2406,3 +2465,271 @@ void MainWindow::setDefaultSaveDir()
   QSettings settings;
   settings.setValue("default_saveas_dir", def_save_dir);
 }
+void MainWindow::setupViewer(Viewer* viewer, SubViewer* subviewer=NULL)
+{
+  // do not save the state of the viewer (anoying)
+  viewer->setStateFileName(QString::null);
+  viewer->textRenderer()->setScene(scene);
+  viewer->setScene(scene);
+  connect(scene, SIGNAL(dataChanged(const QModelIndex &, const QModelIndex & )),
+          viewer, SLOT(update()));
+  connect(scene, SIGNAL(updated()),
+          viewer, SLOT(update()));
+
+  if(subviewer == NULL)
+  {
+    connect(ui->actionRecenterScene, SIGNAL(triggered()),
+            viewer, SLOT(update()));
+
+    connect(ui->actionRecenterScene, SIGNAL(triggered()),
+            this, SLOT(on_actionRecenterScene_triggered()));
+    connect(ui->actionLookAt, SIGNAL(triggered()),
+            this, SLOT(on_actionLookAt_triggered()));
+    connect(ui->actionSetBackgroundColor, SIGNAL(triggered()),
+            this, SLOT(on_actionSetBackgroundColor_triggered()));
+    connect(ui->actionDumpCamera, SIGNAL(triggered()),
+            this, SLOT(on_actionDumpCamera_triggered()));
+    connect(ui->actionCopyCamera, SIGNAL(triggered()),
+            this, SLOT(on_actionCopyCamera_triggered()));
+    connect(ui->actionPasteCamera, SIGNAL(triggered()),
+            this, SLOT(on_actionPasteCamera_triggered()));
+    connect(ui->actionAntiAliasing, SIGNAL(toggled(bool)),
+            viewer, SLOT(setAntiAliasing(bool)));
+    connect(ui->actionDrawTwoSides, SIGNAL(toggled(bool)),
+            viewer, SLOT(setTwoSides(bool)));
+    connect(ui->actionQuickCameraMode, SIGNAL(toggled(bool)),
+            viewer, SLOT(setFastDrawing(bool)));
+    connect(ui->actionSwitchProjection, SIGNAL(toggled(bool)),
+            viewer, SLOT(SetOrthoProjection(bool)));
+    connect(ui->actionSet_Transparency_Pass_Number, SIGNAL(triggered()),
+            viewer, SLOT(setTotalPass_clicked()));
+  }
+  else
+  {
+    QAction* action = subviewer->findChild<QAction*>("actionRecenter");
+    connect(action, SIGNAL(triggered()),
+            viewer, SLOT(update()));
+    connect(action, &QAction::triggered,
+            subviewer, &SubViewer::recenter);
+    action= subviewer->findChild<QAction*>("actionLookat");
+    connect(action, SIGNAL(triggered()),
+            subviewer, SLOT(lookat()));
+    action= subviewer->findChild<QAction*>("actionColor");
+    connect(action, &QAction::triggered,
+            subviewer, &SubViewer::color);
+    action= subviewer->findChild<QAction*>("actionDumpCamera");
+    connect(action, &QAction::triggered,
+            [this, viewer](){
+      information(QString("Camera: %1")
+                  .arg(cameraString(viewer)));
+    });
+    action= subviewer->findChild<QAction*>("actionCopyCamera");
+    connect(action, &QAction::triggered,
+            [this, viewer](){
+      qApp->clipboard()->setText(cameraString(viewer));
+    });
+    action= subviewer->findChild<QAction*>("actionPasteCamera");
+    connect(action, &QAction::triggered,
+            this, [viewer](){
+      QString s = qApp->clipboard()->text();
+      viewer->moveCameraToCoordinates(s, 0.5f);
+    });
+    action= subviewer->findChild<QAction*>("actionAntiAliasing");
+    connect(action, SIGNAL(toggled(bool)),
+            viewer, SLOT(setAntiAliasing(bool)));
+    action= subviewer->findChild<QAction*>("actionDrawTwoSide");
+    connect(action, SIGNAL(toggled(bool)),
+            viewer, SLOT(setTwoSides(bool)));
+    action= subviewer->findChild<QAction*>("actionQuick");
+    connect(action, SIGNAL(toggled(bool)),
+            viewer, SLOT(setFastDrawing(bool)));
+    action= subviewer->findChild<QAction*>("actionOrtho");
+    connect(action, SIGNAL(toggled(bool)),
+            viewer, SLOT(SetOrthoProjection(bool)));
+    action= subviewer->findChild<QAction*>("actionTotalPass");
+    connect(action, &QAction::triggered,
+            viewer, &Viewer::setTotalPass_clicked);
+
+  }
+
+
+  connect(viewer, SIGNAL(requestContextMenu(QPoint)),
+          this, SLOT(contextMenuRequested(QPoint)));
+  connect(viewer, SIGNAL(selected(int)),
+          this, SLOT(selectSceneItem(int)));
+  connect(viewer, SIGNAL(selectedPoint(double, double, double)),
+          this, SLOT(showSelectedPoint(double, double, double)));
+
+  connect(viewer, SIGNAL(selectionRay(double, double, double,
+                                      double, double, double)),
+          scene, SIGNAL(selectionRay(double, double, double,
+                                     double, double, double)));
+
+  connect(viewer, SIGNAL(sendMessage(QString)),
+          this, SLOT(information(QString)));
+
+}
+
+void MainWindow::on_actionAdd_Viewer_triggered()
+{
+  Viewer *viewer2 = new Viewer(ui->centralwidget, viewer);
+  viewer2->setManipulatedFrame(viewer->manipulatedFrame());
+  CGAL::qglviewer::Vec min, max;
+  computeViewerBBox(min, max);
+  updateViewerBbox(viewer2, true, min, max);
+  viewer2->camera()->interpolateToFitScene();
+  viewer2->setObjectName("viewer2");
+  connect(viewer2, SIGNAL(doneInitGL(CGAL::Three::Viewer_interface*)),
+          scene, SLOT(newViewer(CGAL::Three::Viewer_interface*)));
+  SubViewer* sub_viewer = new SubViewer(this, viewer2);
+  ui->viewerLayout->addWidget(sub_viewer);
+  setupViewer(viewer2, sub_viewer);
+  connect(sub_viewer->ui->exitButton, &QPushButton::clicked,
+          [this, sub_viewer](){
+    scene->removeViewer(sub_viewer->viewer);
+    sub_viewer->deleteLater();});
+
+}
+
+void MainWindow::recenterViewer()
+{
+  scene->computeBbox();
+  scene->computeVisibleBbox();
+  CGAL::qglviewer::Vec min, max;
+  computeViewerBBox(min, max);
+  Viewer* target = qobject_cast<Viewer*>(childAt(cursor().pos()));
+  if(target)
+  {
+    scene->computeBbox();
+    updateViewerBbox(target, true, min, max);
+    target->camera()->interpolateToFitScene();
+  }
+}
+
+void MainWindow::updateViewerBbox(Viewer *vi, bool recenter,
+                                  CGAL::qglviewer::Vec min, 
+                                  CGAL::qglviewer::Vec max){
+
+  CGAL::qglviewer::Vec center = viewer->camera()->pivotPoint();
+  vi->setSceneBoundingBox(min,
+                          max);
+  if(recenter)
+  {
+    vi->resetFov();
+    vi->camera()->showEntireScene();
+  }
+  else
+  {
+    vi->camera()->setPivotPoint(center);
+  }
+}
+
+QObject* MainWindow::getDirectChild(QObject* widget)
+{
+
+    if(!widget->property("helpText").toString().isEmpty())
+      return widget;
+  return getDirectChild(widget->parent());
+}
+
+SubViewer::SubViewer(MainWindow* mw, Viewer* viewer)
+  :QWidget(mw),
+    mw(mw),
+    viewer(viewer),
+    viewMenu(new QMenu(this))
+{
+  ui = new Ui::SubViewer;
+  ui->setupUi(this);
+  ui->mainLayout->addWidget(viewer, 1);
+  ui->menuButton->setMenu(viewMenu);
+  ui->menuButton->setProperty("helpText", QString("This is the view menu for this Viewer. \n"
+                                                  "It holds independant display options."));
+  ui->exitButton->setProperty("helpText", QString("Click here to close this Viewer."));
+
+
+  QAction* actionRecenter = new QAction("Re&center Scene",this);
+  actionRecenter->setObjectName("actionRecenter");
+  viewMenu->addAction(actionRecenter);
+  QAction* actionLookat = new QAction("&Look at...",this);
+  actionLookat->setObjectName("actionLookat");
+  viewMenu->addAction(actionLookat);
+  QAction* actionColor = new QAction("Change &Background Color...",this);
+  actionColor->setObjectName("actionColor");
+  viewMenu->addAction(actionColor);
+  QAction* actionDumpCamera = new QAction("&Dump Camera Coordinates",this);
+  actionDumpCamera->setObjectName("actionDumpCamera");
+  QAction* actionCopyCamera = new QAction("&Copy Camera",this);
+  actionCopyCamera->setObjectName("actionCopyCamera");
+  QAction* actionPasteCamera = new QAction("&Paste Camera",this);
+  actionPasteCamera->setObjectName("actionPasteCamera");
+  QMenu* cameraMenu = new QMenu("Camera", mw);
+  cameraMenu->addAction(actionDumpCamera);
+  cameraMenu->addAction(actionCopyCamera);
+  cameraMenu->addAction(actionPasteCamera);
+  viewMenu->addMenu(cameraMenu);
+
+  QAction* actionAntiAliasing = new QAction("&Antialiasing",this);
+  actionAntiAliasing->setObjectName("actionAntiAliasing");
+  actionAntiAliasing->setCheckable(true);
+  actionAntiAliasing->setChecked(false);
+  viewMenu->addAction(actionAntiAliasing);
+  QAction* actionDrawTwoSide = new QAction("Draw &Two Sides",this);
+  actionDrawTwoSide->setObjectName("actionDrawTwoSide");
+  actionDrawTwoSide->setCheckable(true);
+  actionDrawTwoSide->setChecked(false);
+  viewMenu->addAction(actionDrawTwoSide);
+  QAction* actionQuick = new QAction("Quick Camera Mode",this);
+  actionQuick->setObjectName("actionQuick");
+  actionQuick->setCheckable(true);
+  actionQuick->setChecked(true);
+  viewMenu->addAction(actionQuick);
+  QAction* actionOrtho = new QAction("Orthographic Projection",this);
+  actionOrtho->setObjectName("actionOrtho");
+  actionOrtho->setCheckable(true);
+  actionOrtho->setChecked(false);
+  viewMenu->addAction(actionOrtho);
+  QAction* actionLight = new QAction("L&ighting...",this);
+  actionLight->setObjectName("actionLight");
+  viewMenu->addAction(actionLight);
+  QAction* actionTotalPass = new QAction("Set Transparency Pass &Number...",this);
+  actionTotalPass->setObjectName("actionTotalPass");
+  viewMenu->addAction(actionTotalPass);
+}
+
+SubViewer::~SubViewer()
+{
+  delete ui;
+  viewer->deleteLater();
+}
+
+void SubViewer::recenter()
+{
+  CGAL::qglviewer::Vec min, max;
+  mw->computeViewerBBox(min, max);
+  mw->updateViewerBbox(viewer, true, min, max);
+  viewer->camera()->interpolateToFitScene();
+}
+
+void SubViewer::lookat()
+{
+  Show_point_dialog dialog(mw);
+  dialog.setWindowTitle(tr("Look at..."));
+  int i = dialog.exec();
+  if( i == QDialog::Accepted &&
+      dialog.has_correct_coordinates() )
+  {
+      mw->viewerShow(viewer,
+                 (float)dialog.get_x(),
+                 (float)dialog.get_y(),
+                 (float)dialog.get_z());
+  }
+}
+
+void SubViewer::color()
+{
+  QColor c =  QColorDialog::getColor();
+  if(c.isValid()) {
+    viewer->setBackgroundColor(c);
+    viewer->update();
+  }
+}
diff --git a/Polyhedron/demo/Polyhedron/MainWindow.h b/Polyhedron/demo/Polyhedron/MainWindow.h
index a3be3f9ab87..cb3245f87c5 100644
--- a/Polyhedron/demo/Polyhedron/MainWindow.h
+++ b/Polyhedron/demo/Polyhedron/MainWindow.h
@@ -19,6 +19,7 @@
 #include <QModelIndex>
 class Scene;
 class Viewer;
+struct SubViewer;
 class QTreeView;
 class QMenu;
 namespace CGAL {
@@ -26,6 +27,10 @@ namespace Three{
 class Polyhedron_demo_io_plugin_interface;
 class Polyhedron_demo_plugin_interface;
 class Scene_item;
+class Viewer_interface;
+}
+namespace qglviewer{
+class Vec;
 }
 }
 
@@ -33,6 +38,7 @@ class QSortFilterProxyModel;
 
 namespace Ui {
   class MainWindow;
+  class SubViewer;
   class Statistics_on_item_dialog;
 }
 
@@ -81,7 +87,7 @@ public:
    * throws `std::logic_error` if loading does not succeed or
    * `std::invalid_argument` if `fileinfo` specifies an invalid file*/
   CGAL::Three::Scene_item* loadItem(QFileInfo fileinfo, CGAL::Three::Polyhedron_demo_io_plugin_interface*);
-
+  
 Q_SIGNALS:
   //! Is emitted when the Application is closed.
   void on_closure();
@@ -96,7 +102,7 @@ public Q_SLOTS:
   void makeNewGroup();
   //! Re-computes the viewer's Bbox
   //! If `b` is true, recenters the scene.
-  void updateViewerBBox(bool b);
+  void updateViewersBboxes(bool recenter);
   //! Opens a script or a file with the default loader if there is.
   void open(QString);
   //! Is called when the up button is pressed.
@@ -193,21 +199,21 @@ public Q_SLOTS:
   void addAction(QString actionName,
                  QString actionText,
                  QString menuName);
-  /*!
-   * Sets the scene center to the target position and makes the
-   * scene slide to this new center. Also sets the pivotPoint of
-   * the camera to this position.
-   */
-  void viewerShow(float, float, float);
-  /*!
-   * Sets the scene center to be the center of the target BBox.
-   * Also sets the pivotPoint of the camera to this position.
-   */
-  void viewerShow(float, float, float, float, float, float);
-  /*!
-   * Centers the scene on the target object.
-   */
-  void viewerShowObject();
+  
+  /*! Sets the scene center to the target position and makes the
+  * scene slide to this new center. Also sets the pivotPoint of
+  * the camera to this position.
+  */
+ void viewerShow(CGAL::Three::Viewer_interface *viewer, float, float, float);
+ /*!
+  * Sets the scene center to be the center of the target BBox.
+  * Also sets the pivotPoint of the camera to this position.
+  */
+ void viewerShow(float, float, float, float, float, float);
+ /*!
+  * Centers the scene on the target object.
+  */
+ void viewerShowObject();
   /*!
    * Displays a text preceded by the mention "INFO :".
    */
@@ -335,7 +341,7 @@ protected Q_SLOTS:
    */
   void on_actionLookAt_triggered();
   //!Returns the position and orientation of the current camera frame.
-  QString cameraString() const;
+    QString cameraString(CGAL::Three::Viewer_interface *v) const;
   /*! Prints the position and orientation of the current camera frame.
    * @see cameraString()
    */
@@ -383,7 +389,9 @@ protected:
   //! Returns a list of the selected items in the Geometric Objects view.
   QList<int> getSelectedSceneItemIndices() const;
 private:
+  QObject* getDirectChild(QObject* widget);
   void updateMenus();
+  void setupViewer(Viewer* viewer, SubViewer *subviewer);
   bool load_plugin(QString names, bool blacklisted);
   void recurseExpand(QModelIndex index);
   QMap<QString, QMenu*> menu_map;
@@ -438,6 +446,29 @@ private:
   QLineEdit operationSearchBar;
   QWidgetAction* searchAction;
   QString def_save_dir;
+  void computeViewerBBox(CGAL::qglviewer::Vec &min, CGAL::qglviewer::Vec &max);
+  void updateViewerBbox(Viewer* vi, bool recenter, CGAL::qglviewer::Vec min, 
+                        CGAL::qglviewer::Vec max);
+  
+private Q_SLOTS:
+  void on_actionAdd_Viewer_triggered();
+  void recenterViewer();
 };
+  
+struct SubViewer : public QWidget
+{
+  Q_OBJECT
+public:
+  MainWindow* mw;
+  Viewer* viewer;
+  Ui::SubViewer* ui;
+  QMenu* viewMenu;
 
+  SubViewer(MainWindow* mw, Viewer* viewer);
+  ~SubViewer();
+public Q_SLOTS:
+  void recenter();
+  void lookat();
+  void color();
+};
 #endif // ifndef MAINWINDOW_H
diff --git a/Polyhedron/demo/Polyhedron/MainWindow.ui b/Polyhedron/demo/Polyhedron/MainWindow.ui
index 5065f1d63cc..c7d3c056f3b 100644
--- a/Polyhedron/demo/Polyhedron/MainWindow.ui
+++ b/Polyhedron/demo/Polyhedron/MainWindow.ui
@@ -20,14 +20,18 @@
   <widget class="QWidget" name="centralwidget">
    <layout class="QVBoxLayout" name="verticalLayout_2">
     <item>
-     <widget class="Viewer" name="viewer" native="true">
-      <property name="sizePolicy">
-       <sizepolicy hsizetype="Preferred" vsizetype="Preferred">
-        <horstretch>0</horstretch>
-        <verstretch>1</verstretch>
-       </sizepolicy>
-      </property>
-     </widget>
+     <layout class="QHBoxLayout" name="viewerLayout">
+      <item>
+       <widget class="Viewer" name="viewer" native="true">
+        <property name="sizePolicy">
+         <sizepolicy hsizetype="Preferred" vsizetype="Preferred">
+          <horstretch>0</horstretch>
+          <verstretch>1</verstretch>
+         </sizepolicy>
+        </property>
+       </widget>
+      </item>
+     </layout>
     </item>
    </layout>
   </widget>
@@ -95,6 +99,7 @@
     <addaction name="actionLookAt"/>
     <addaction name="actionDrawTwoSides"/>
     <addaction name="actionSwitchProjection"/>
+    <addaction name="actionAdd_Viewer"/>
     <addaction name="menuDockWindows"/>
     <addaction name="menuCamera"/>
     <addaction name="separator"/>
@@ -492,12 +497,18 @@
     <string>Set Different Colors for Selected Items</string>
    </property>
   </action>
+  <action name="actionAdd_Viewer">
+   <property name="text">
+    <string>Add &amp;Viewer</string>
+   </property>
+  </action>
  </widget>
  <customwidgets>
   <customwidget>
    <class>Viewer</class>
    <extends>QWidget</extends>
    <header>Viewer.h</header>
+   <container>1</container>
   </customwidget>
  </customwidgets>
  <resources>
diff --git a/Polyhedron/demo/Polyhedron/Scene.cpp b/Polyhedron/demo/Polyhedron/Scene.cpp
index 7e4e0fcf240..a1bdef72667 100644
--- a/Polyhedron/demo/Polyhedron/Scene.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene.cpp
@@ -435,10 +435,10 @@ void Scene::initializeGL(CGAL::Three::Viewer_interface* viewer)
   vbo[1].create();
   
   viewer->makeCurrent();
-  vao = new QOpenGLVertexArrayObject();
-  vao->create();
+  vaos[viewer] = new QOpenGLVertexArrayObject();
+  vaos[viewer]->create();
   program.bind();
-  vao->bind();
+  vaos[viewer]->bind();
   vbo[0].bind();
   vbo[0].allocate(points, 18 * sizeof(float));
   program.enableAttributeArray("vertex");
@@ -450,7 +450,7 @@ void Scene::initializeGL(CGAL::Three::Viewer_interface* viewer)
   program.enableAttributeArray("v_texCoord");
   program.setAttributeArray("v_texCoord", GL_FLOAT, 0, 2);
   vbo[1].release();
-  vao->release();
+  vaos[viewer]->release();
   program.release();
   gl_init = true;
 }
@@ -778,7 +778,7 @@ Scene::draw_aux(bool with_names, CGAL::Three::Viewer_interface* viewer)
    
       //blending
       program.bind();
-      vao->bind();
+      vaos[viewer]->bind();
       viewer->glClearColor(background.redF(),
                            background.greenF(),
                            background.blueF(),
@@ -802,7 +802,7 @@ Scene::draw_aux(bool with_names, CGAL::Three::Viewer_interface* viewer)
       }
       viewer->glDisable(GL_BLEND);
       viewer->glEnable(GL_DEPTH_TEST);
-      vao->release();
+      vaos[viewer]->release();
       program.release();
     }
    
@@ -1201,6 +1201,7 @@ void Scene::itemVisibilityChanged(CGAL::Three::Scene_item* item)
      && !item->isEmpty())
   {
     //does not recenter
+    computeVisibleBbox();
     Q_EMIT updated_bbox(false);
   }
 }
@@ -1662,3 +1663,75 @@ void Scene::adjustIds(Item_id removed_id)
     m_entries[i]->setId(i-1);//the signal is emitted before m_entries is amputed from the item, so new id is current id -1.
   }
 }
+
+void Scene::computeVisibleBbox()
+{
+  if(m_entries.empty())
+  {
+    last_visible_bbox = Bbox(0,0,0,0,0,0);
+    return;
+  }
+
+  bool bbox_initialized = false;
+  Bbox bbox = Bbox(0,0,0,0,0,0);
+  Q_FOREACH(CGAL::Three::Scene_item* item, m_entries)
+  {
+    if(item->isFinite() && !item->isEmpty() && item->visible()) {
+      if(bbox_initialized) {
+
+        bbox = bbox + item->bbox();
+      }
+      else {
+        bbox = item->bbox();
+        bbox_initialized = true;
+
+      }
+    }
+
+  }
+  last_visible_bbox = bbox;
+}
+
+void Scene::computeBbox()
+{
+  if(m_entries.empty())
+  {
+    last_bbox = Bbox(0,0,0,0,0,0);
+    return;
+  }
+
+  bool bbox_initialized = false;
+  Bbox bbox = Bbox(0,0,0,0,0,0);
+  Q_FOREACH(CGAL::Three::Scene_item* item, m_entries)
+  {
+    if(item->isFinite() && !item->isEmpty() ) {
+      if(bbox_initialized) {
+
+        bbox = bbox + item->bbox();
+      }
+      else {
+        bbox = item->bbox();
+        bbox_initialized = true;
+
+      }
+    }
+
+  }
+  last_bbox = bbox;
+}
+
+void Scene::removeViewer(Viewer_interface *viewer)
+{
+  vaos[viewer]->destroy();
+  vaos[viewer]->deleteLater();
+  vaos.remove(viewer);
+  Q_FOREACH(Scene_item* item, m_entries)
+  {
+    item->removeViewer(viewer);
+  }
+}
+
+Scene::Bbox Scene::visibleBbox() const
+{
+    return last_visible_bbox;
+}
diff --git a/Polyhedron/demo/Polyhedron/Scene.h b/Polyhedron/demo/Polyhedron/Scene.h
index aa778970fb7..ca862d87539 100644
--- a/Polyhedron/demo/Polyhedron/Scene.h
+++ b/Polyhedron/demo/Polyhedron/Scene.h
@@ -93,6 +93,9 @@ public:
   void updatePrimitiveIds(Viewer_interface *, Scene_item *item) Q_DECL_OVERRIDE;
   bool testDisplayId(double x, double y, double z, CGAL::Three::Viewer_interface* viewer) Q_DECL_OVERRIDE;
   Bbox bbox() const Q_DECL_OVERRIDE;
+  Bbox visibleBbox() const ;
+  void computeBbox();
+  void computeVisibleBbox();
   double len_diagonal() const Q_DECL_OVERRIDE
   {
     Bbox box = bbox();
@@ -278,9 +281,12 @@ private:
   float points[18];
   float uvs[12];
   QOpenGLShaderProgram program;
-  QOpenGLVertexArrayObject* vao;
+  QMap<CGAL::Three::Viewer_interface*, QOpenGLVertexArrayObject*> vaos;
   mutable QOpenGLBuffer vbo[2];
-
+  Bbox last_bbox;
+  Bbox last_visible_bbox;
+public:
+  void removeViewer(CGAL::Three::Viewer_interface*);
 }; // end class Scene
 
 class QAbstractProxyModel;
@@ -316,6 +322,7 @@ private:
   QAbstractProxyModel *proxy;
   Scene *scene;
   mutable int size;
+  
 }; // end class SceneDelegate
 
 #endif // SCENE_H
diff --git a/Polyhedron/demo/Polyhedron/Scene_group_item.cpp b/Polyhedron/demo/Polyhedron/Scene_group_item.cpp
index 0a3c31f6653..34be29ac0fc 100644
--- a/Polyhedron/demo/Polyhedron/Scene_group_item.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene_group_item.cpp
@@ -15,8 +15,7 @@ Scene_group_item::Scene_group_item(QString name, int nb_vbos, int nb_vaos )
 bool Scene_group_item::isFinite() const
 {
   Q_FOREACH(Scene_interface::Item_id id, children)
-    if(!getChild(id)->isFinite()){
-      return false;
+    if(!getChild(id)->isFinite()){      return false;
     }
   return true;
 }
@@ -246,3 +245,5 @@ void Scene_group_item::setAlpha(int )
   }
 }
 
+void Scene_group_item::removeViewer(CGAL::Three::Viewer_interface*)
+{}
diff --git a/Polyhedron/demo/Polyhedron/Scene_item_rendering_helper.cpp b/Polyhedron/demo/Polyhedron/Scene_item_rendering_helper.cpp
index c4b6e12b0e3..05101473627 100644
--- a/Polyhedron/demo/Polyhedron/Scene_item_rendering_helper.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene_item_rendering_helper.cpp
@@ -242,3 +242,19 @@ void Scene_item_rendering_helper::setBuffersInit(Viewer_interface* viewer, bool
 {
   priv->buffers_init[viewer] = val;
 }
+
+void Scene_item_rendering_helper::removeViewer(Viewer_interface *viewer)
+{
+  Q_FOREACH(Triangle_container* tc, priv->triangle_containers)
+  {
+    tc->removeViewer(viewer);
+  }
+  Q_FOREACH(Edge_container* ec, priv->edge_containers)
+  {
+    ec->removeViewer(viewer);
+  }
+  Q_FOREACH(Point_container* pc, priv->point_containers)
+  {
+    pc->removeViewer(viewer);
+  }
+}
diff --git a/Polyhedron/demo/Polyhedron/Scene_polygon_soup_item.h b/Polyhedron/demo/Polyhedron/Scene_polygon_soup_item.h
index f2deb9fadf7..e422b126c6d 100644
--- a/Polyhedron/demo/Polyhedron/Scene_polygon_soup_item.h
+++ b/Polyhedron/demo/Polyhedron/Scene_polygon_soup_item.h
@@ -152,6 +152,7 @@ public:
     const Polygons& polygons() const;
     const Edges& non_manifold_edges() const;
 
+    void removeViewer(CGAL::Three::Viewer_interface*)Q_DECL_OVERRIDE{}
 public Q_SLOTS:
     void shuffle_orientations();
     bool orient();
diff --git a/Polyhedron/demo/Polyhedron/SubViewer.ui b/Polyhedron/demo/Polyhedron/SubViewer.ui
new file mode 100644
index 00000000000..9a7104eef15
--- /dev/null
+++ b/Polyhedron/demo/Polyhedron/SubViewer.ui
@@ -0,0 +1,88 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>SubViewer</class>
+ <widget class="QWidget" name="SubViewer">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>400</width>
+    <height>240</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string>Form</string>
+  </property>
+  <layout class="QVBoxLayout" name="verticalLayout_2" stretch="0">
+   <item>
+    <layout class="QVBoxLayout" name="mainLayout">
+     <item>
+      <layout class="QHBoxLayout" name="horizontalLayout">
+       <item>
+        <spacer name="horizontalSpacer">
+         <property name="orientation">
+          <enum>Qt::Horizontal</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>40</width>
+           <height>10</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+       <item>
+        <widget class="QPushButton" name="menuButton">
+         <property name="text">
+          <string/>
+         </property>
+         <property name="icon">
+          <iconset resource="Polyhedron_3.qrc">
+           <normaloff>:/cgal/icons/menu</normaloff>:/cgal/icons/menu</iconset>
+         </property>
+         <property name="iconSize">
+          <size>
+           <width>10</width>
+           <height>10</height>
+          </size>
+         </property>
+         <property name="default">
+          <bool>false</bool>
+         </property>
+         <property name="flat">
+          <bool>true</bool>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <widget class="QPushButton" name="exitButton">
+         <property name="text">
+          <string/>
+         </property>
+         <property name="icon">
+          <iconset resource="Polyhedron_3.qrc">
+           <normaloff>:/cgal/icons/exit</normaloff>:/cgal/icons/exit</iconset>
+         </property>
+         <property name="iconSize">
+          <size>
+           <width>10</width>
+           <height>10</height>
+          </size>
+         </property>
+         <property name="flat">
+          <bool>true</bool>
+         </property>
+        </widget>
+       </item>
+      </layout>
+     </item>
+    </layout>
+   </item>
+  </layout>
+ </widget>
+ <resources>
+  <include location="Polyhedron_3.qrc"/>
+  <include location="Polyhedron_3.qrc"/>
+ </resources>
+ <connections/>
+</ui>
diff --git a/Polyhedron/demo/Polyhedron/Viewer.cpp b/Polyhedron/demo/Polyhedron/Viewer.cpp
index cd27d55bda8..ca4d15b60b7 100644
--- a/Polyhedron/demo/Polyhedron/Viewer.cpp
+++ b/Polyhedron/demo/Polyhedron/Viewer.cpp
@@ -23,12 +23,13 @@
 #include <QByteArray>
 #include <QBuffer>
 #endif
-
+#define ORIGINAL_FOV 0.94853805396568136
 
 class Viewer_impl {
 public:
   CGAL::Three::Scene_draw_interface* scene;
   Viewer *viewer;
+  Viewer *shareViewer;
   bool antialiasing;
   bool twosides;
   bool macro_mode;
@@ -97,9 +98,13 @@ public:
   void clearDistancedisplay();
   void draw_aux(bool with_names, Viewer*);
   //! Contains all the programs for the item rendering.
-  mutable std::vector<QOpenGLShaderProgram*> shader_programs;
+  static std::vector<QOpenGLShaderProgram*> shader_programs;
   QMatrix4x4 projectionMatrix;
   void sendSnapshotToClipboard(Viewer*);
+  std::vector<QOpenGLShaderProgram*>& shaderPrograms()
+  {
+    return shader_programs;
+  }
 };
 
 class LightingDialog :
@@ -211,10 +216,10 @@ private:
   QColorDialog spec_dial;
 };
 
-Viewer::Viewer(QWidget* parent, bool antialiasing)
-  : CGAL::Three::Viewer_interface(parent)
+std::vector<QOpenGLShaderProgram*> Viewer_impl::shader_programs = 
+    std::vector<QOpenGLShaderProgram*>(Viewer::NB_OF_PROGRAMS);
+void Viewer::doBindings()
 {
-  d = new Viewer_impl;
   QSettings viewer_settings;
   // enable anti-aliasing
   QString cam_pos = viewer_settings.value("cam_pos", QString("0.0,0.0,1.0")).toString();
@@ -245,7 +250,6 @@ Viewer::Viewer(QWidget* parent, bool antialiasing)
   d->scene = 0;
   d->projection_is_ortho = false;
   d->initialized = false;
-  d->antialiasing = antialiasing;
   d->twosides = false;
   this->setProperty("draw_two_sides", false);
   d->macro_mode = false;
@@ -306,6 +310,32 @@ Viewer::Viewer(QWidget* parent, bool antialiasing)
   setTextIsEnabled(true);
 }
 
+Viewer::Viewer(QWidget* parent, bool antialiasing)
+  : CGAL::Three::Viewer_interface(parent)
+{
+  d = new Viewer_impl;
+  d->antialiasing = antialiasing;
+  doBindings();
+}
+
+Viewer::Viewer(QWidget* parent,
+               Viewer* sharedWidget,
+               bool antialiasing)
+  : CGAL::Three::Viewer_interface(parent, sharedWidget)
+{
+  d = new Viewer_impl;
+  d->viewer = this;
+  d->shareViewer = sharedWidget;
+  is_sharing = true;
+  d->antialiasing = antialiasing;
+  this->setProperty("draw_two_sides", false);
+  this->setProperty("helpText", QString("This is a sub-viewer. It displays the scene "
+                                        "from another point of view. \n "));
+  is_ogl_4_3 = sharedWidget->is_ogl_4_3;
+  d->_recentFunctions = sharedWidget->d->_recentFunctions;
+  doBindings();
+}
+
 Viewer::~Viewer()
 {
     QSettings viewer_settings;
@@ -1639,5 +1669,10 @@ void Viewer::setGlPointSize(const GLfloat &p) { d->gl_point_size = p; }
 
 const GLfloat& Viewer::getGlPointSize() const { return d->gl_point_size; }
 
+void Viewer::resetFov()
+{
+  camera()->setHorizontalFieldOfView(ORIGINAL_FOV);
+}
+
 #include "Viewer.moc"
 
diff --git a/Polyhedron/demo/Polyhedron/Viewer.h b/Polyhedron/demo/Polyhedron/Viewer.h
index 19895e80ded..888b170dc2f 100644
--- a/Polyhedron/demo/Polyhedron/Viewer.h
+++ b/Polyhedron/demo/Polyhedron/Viewer.h
@@ -16,6 +16,10 @@
 #include <CGAL/Three/TextRenderer.h>
 // forward declarations
 class QWidget;
+class QMouseEvent;
+class QKeyEvent;
+class QContextMenuEvent;
+class Viewer_impl;
 namespace CGAL{
 namespace Three{
 class Scene_draw_interface;
@@ -34,6 +38,7 @@ class VIEWER_EXPORT Viewer : public CGAL::Three::Viewer_interface {
 
 public:
   Viewer(QWidget * parent, bool antialiasing = false);
+  Viewer(QWidget * parent, Viewer *sharedWidget, bool antialiasing = false);
   ~Viewer();
   bool testDisplayId(double, double, double)Q_DECL_OVERRIDE;
   void updateIds(CGAL::Three::Scene_item *)Q_DECL_OVERRIDE;
@@ -85,9 +90,10 @@ public:
   const QImage& staticImage() const Q_DECL_OVERRIDE;
   //!Set total number of depth peeling passes.
    void setTotalPass(int);
-
+   void resetFov();
 Q_SIGNALS:
   void sendMessage(QString);
+  void doneInitGL(CGAL::Three::Viewer_interface*);
 public Q_SLOTS:
   //! Sets the antialiasing to true or false.
   void setAntiAliasing(bool b) Q_DECL_OVERRIDE;
@@ -122,6 +128,7 @@ public Q_SLOTS:
   void setLighting();
 
   void messageLogged(QOpenGLDebugMessage);
+  void initializeGL()Q_DECL_OVERRIDE;
 
 protected:
   void paintEvent(QPaintEvent *)Q_DECL_OVERRIDE;
@@ -142,6 +149,7 @@ protected:
   friend class Viewer_impl;
   Viewer_impl* d;
   double prev_radius;
+  void doBindings();
 
 public:
   QOpenGLFunctions_4_3_Core* openGL_4_3_functions() Q_DECL_OVERRIDE;
diff --git a/Three/include/CGAL/Three/Scene_group_item.h b/Three/include/CGAL/Three/Scene_group_item.h
index c962d0642f7..7af8890d425 100644
--- a/Three/include/CGAL/Three/Scene_group_item.h
+++ b/Three/include/CGAL/Three/Scene_group_item.h
@@ -237,7 +237,7 @@ public :
     void moveUp(int);
     //!Moves a child down in the list.
     void moveDown(int);
-
+    void removeViewer(CGAL::Three::Viewer_interface* )Q_DECL_OVERRIDE;
 public Q_SLOTS:
     //!\brief Redraws children.
     //!
diff --git a/Three/include/CGAL/Three/Scene_item.h b/Three/include/CGAL/Three/Scene_item.h
index 02e154cc92a..2ca17fd7898 100644
--- a/Three/include/CGAL/Three/Scene_item.h
+++ b/Three/include/CGAL/Three/Scene_item.h
@@ -301,6 +301,12 @@ public:
 
   //!Contains the number of group and subgroups containing this item.
   int has_group;
+  //!
+  //! \brief removeViewer removes the Vaos fo `viewer`.
+  //!
+  //! Must be overriden;
+  //!
+  virtual void removeViewer(CGAL::Three::Viewer_interface* viewer) = 0;
 
 public Q_SLOTS:
 
diff --git a/Three/include/CGAL/Three/Scene_item_rendering_helper.h b/Three/include/CGAL/Three/Scene_item_rendering_helper.h
index e8e729810ed..186cd10e63f 100644
--- a/Three/include/CGAL/Three/Scene_item_rendering_helper.h
+++ b/Three/include/CGAL/Three/Scene_item_rendering_helper.h
@@ -190,6 +190,9 @@ public:
   //! @returns the item's bounding box's diagonal length.
   //! @todo must replace the one from Scene_item eventually
   virtual double diagonalBbox() const Q_DECL_OVERRIDE;
+  //! \brief removeViewer removes the Vaos for `viewer`.
+  //! \param viewer the viewer to be removed.
+  void removeViewer(Viewer_interface *viewer) Q_DECL_OVERRIDE;
 protected:
 
 
diff --git a/Three/include/CGAL/Three/Viewer_interface.h b/Three/include/CGAL/Three/Viewer_interface.h
index 0c78e97c68b..0ae1ec09a92 100644
--- a/Three/include/CGAL/Three/Viewer_interface.h
+++ b/Three/include/CGAL/Three/Viewer_interface.h
@@ -107,6 +107,14 @@ public:
   //! Creates a valid context for OpenGL ES 2.0.
   //! \param parent the parent widget. It usually is the MainWindow.
   Viewer_interface(QWidget* parent) : CGAL::QGLViewer(parent) {}
+  //!
+  //! \brief Constructor for the secondary viewers.
+  //!
+  //! \param parent the parent widget. It usually is the MainWindow.
+  //! \param sharedWidget the main viewer of the Application. This will share the
+  //!  context and allow synchronized rendering of multiple views.
+  //!
+  Viewer_interface(QWidget* parent, QWidget*) : QGLViewer(parent){}
   virtual ~Viewer_interface() {}
 
   //! \brief Sets the scene for the viewer.