A canvas server

  class draw_srv : public canvas {  
  public:
  
  draw_srv( const widget* w,  char* path ) : canvas(w,path) {  
 (a)
          geometry(200,100);
          self()->bind(this);
          dragging = 0;
  }
  
  void press( event& ) { dragging = 1; }
  
  void motion( event& e) { 
          if (dragging) circle(e.x(),e.y(),10,"-fill black");
  }
  
  void release( event&  ) { dragging = 0; }
  
  protected:
  int dragging;
  };