diff --git a/src/gui_builder.cc b/src/gui_builder.cc
index 1461414..d6fc9b7 100644
--- a/src/gui_builder.cc
+++ b/src/gui_builder.cc
@@ -24,6 +24,9 @@
 #include "schedulables_widget.hh"
 #include "gui_builder.hh"
 
+#include "backend/history.hh"
+#include "backend/simulation.hh"
+
 #include <glibmm/ustring.h>
 #include <gtkmm/aboutdialog.h>
 #include <gtkmm/expander.h>
@@ -64,6 +67,10 @@ GuiBuilder::GuiBuilder(const std::string& gladefile)
 	scheds_expander->add(*scheds_widget);
 	// we have to remember to manually show custom added widgets:
 	scheds_widget->show();
+
+  // A test for widget display:
+  Simulation& sim = Simulation::get_instance();
+  sim.get_history().add_process("goofy", 0, 0);
 }
 
 
diff --git a/src/schedulables_widget.cc b/src/schedulables_widget.cc
index 72438a8..81b58d2 100644
--- a/src/schedulables_widget.cc
+++ b/src/schedulables_widget.cc
@@ -21,45 +21,72 @@
 #include "cairo_elements.hh"
 #include "schedulables_widget.hh"
 
-#include <cmath>
+#include "backend/history.hh"
+#include "backend/simulation.hh"
+
+#include <iostream>
+#include <memory>
 
 using namespace sgpem;
 
 
 SchedulablesWidget::SchedulablesWidget()
-  : Gtk::DrawingArea(), _ctx(NULL)
+  : Gtk::DrawingArea(), _h(1), _buf(NULL)
 {
   // Add other events we want to manage (as mouse clicks)
   // when needed
   add_events(Gdk::EXPOSURE_MASK);
+
+  // Register this observer:
+  Simulation::get_instance().get_history().attach(*this);
 }
  
 
 SchedulablesWidget::~SchedulablesWidget()
 {
-  if(_ctx != NULL)
-    cairo_destroy(_ctx);
+  Simulation::get_instance().get_history().detach(*this);
 }
 
 
 void 
 SchedulablesWidget::update(const History& history)
 {
+  // Determine the final height before to start drawing
+  unsigned int w = get_allocation().get_width();
+  _h = calc_height(history);
+
   // FIXME : write me using double buffering
-  // GdkPixmap* buffer = gdk_pixmap_new(...);
-  // _ctx = gdk_cairo_create(buffer);
+  // PROBLEM : get_window() seems to return a null pointer!!!
+  _buf = Gdk::Pixmap::create(get_window(), w, _h);
+  cairo_t* ctx = gdk_cairo_create(_buf->gobj());
 
   // do the drawing...
+  draw_widget(ctx);
+  
+  cairo_scale(ctx, w, _h);
+
+  // manually force an expose_event?
+  cairo_destroy(ctx);
+}
 
 
+void
+SchedulablesWidget::draw_widget(cairo_t* ctx)
+{
   // NOTE: just to try
-  CairoElements ce(_ctx);
+  CairoElements ce(ctx);
   Color red = { 1, 0, 0 };
   Point center = { 25, 25 };
-
+  
   ce.draw_3dsphere(center, 25, red);
+}
 
-  // manually force an expose_event?  
+
+unsigned int
+SchedulablesWidget::calc_height(const History& history) const
+{
+  // FIXME: write me
+  return 400;
 }
 
  
@@ -69,52 +96,37 @@ SchedulablesWidget::on_size_request(Gtk::Requisition* requisition)
   // FIXME: take correct measures, consider also using a viewport(?)
   *requisition = Gtk::Requisition();
   requisition->width = get_allocation().get_width();
-  requisition->height = requisition->width;
+  requisition->height = _h;
 }
 
 
 bool 
 SchedulablesWidget::on_expose_event(GdkEventExpose* event)
 {
-  // Use double buffering or we're CPU-dead
-  Glib::RefPtr<Gdk::Window> window = get_window();
-  GdkWindow* gdkWindow = window->gobj();
-  GdkDrawable* gdkDrawable;
-  gint xOffset, yOffset;
-  gdk_window_get_internal_paint_info(gdkWindow, &gdkDrawable, &xOffset, &yOffset);
-
-  // Copy new ctx from old one (the buffer); from distant memories,
-  // we should use something like create_similar to instantiate a 
-  // compatible surface and then copy the buffer to fg
-  // So the following two lines WILL HAVE TO CHANGE.
-  if(_ctx == NULL)
-    _ctx = gdk_cairo_create(gdkDrawable);
-
-  cairo_t* cr = gdk_cairo_create(gdkDrawable); 
-  
   const Gtk::Allocation& allocation = get_allocation();
   int width  = allocation.get_width();
   int height = allocation.get_height();
   
   // Clip to redraw only the smallest possible area
-  if(event) 
-    {
-      cairo_rectangle(cr, event->area.x, event->area.y,
-		      event->area.width, event->area.height);
-      cairo_clip(cr);
-    }
-
-  // should be calculated dinamically:
-  set_size_request(200,400);
+  std::auto_ptr<Gdk::Rectangle> clip_area;
+  if(event)
+    clip_area = std::auto_ptr<Gdk::Rectangle>(new Gdk::Rectangle(event->area.x, event->area.y,
+                                                                 event->area.width, event->area.height));
   
-  // Copy from buffer to video
-  // if(_ctx != NULL)
-  //   gdk_draw_drawable(buffer, GC??, gdkDrawable, ...clip-region...);
+  else
+    clip_area = std::auto_ptr<Gdk::Rectangle>(new Gdk::Rectangle(0, 0, width, height));
 
-  // Height should be calculated dynamically?
-  cairo_scale(cr, width, width);
-
-  cairo_destroy(cr);
+  // Use double buffering or we're CPU-dead
+  // Copy from the buffer to the screen
+  if(_buf)
+    get_window()->draw_drawable(Gdk::GC::create(get_window()), _buf, 
+                                clip_area->get_x(), clip_area->get_y(), 
+                                clip_area->get_x(), clip_area->get_y(),
+                                clip_area->get_width(), clip_area->get_height());
+  
+  // calculated dinamically:
+  set_size_request(width, _h);
+  
   return true; 
 }
  
diff --git a/src/schedulables_widget.hh b/src/schedulables_widget.hh
index 71244db..f3de0ec 100644
--- a/src/schedulables_widget.hh
+++ b/src/schedulables_widget.hh
@@ -25,7 +25,9 @@
 
 #include "backend/history_observer.hh"
 
+#include <cairo/cairo.h>
 #include <gtkmm/drawingarea.h>
+#include <gdkmm/pixmap.h>
 
 namespace sgpem
 {
@@ -41,6 +43,12 @@ namespace sgpem
     virtual void on_size_request(Gtk::Requisition* requisition);
     virtual bool on_expose_event(GdkEventExpose* event);
     virtual bool on_button_press_event(GdkEventButton* event);
+    virtual void draw_widget(cairo_t* ctx);
+    virtual unsigned int calc_height(const History& history) const;
+
+    // The height the widget will assume, must be determined
+    // before starting drawing by calc_height().
+    unsigned int               _h;
 
   private:
     typedef Gdk::Rectangle                               area_t;
@@ -48,7 +56,7 @@ namespace sgpem
     typedef std::pair<area_t, method0_t>                 area_callback_t;
     typedef std::vector<area_callback_t>                 areas_vect_t;
     
-    cairo_t*  _ctx;
+    Glib::RefPtr<Gdk::Pixmap>  _buf;
   };
 
 } //~ namespace sgpem