class TButton: public TPad, public TAttText

  A TButton object is a user interface object.
  A TButton has a name and an associated action.
  When the button is clicked with the left mouse button, the cooresponding
  action is executed.
  A Tbutton can be created by direct invokation of the constructors
  or via the graphics editor.
  The Action can be set via TButton::SetMethod.
  The action can be any command. Examples of actions:
     "34+78" When the button is clicked, the result of addition is printed.
     ".x macro.C" . Clicking the button executes the macro macro.C
  The action can be modified at any time via TButton::SetMethod.

  To modify the layout/size/contents of one or several buttons
  in a canvas, you must set the canvas editable via TCanvas::SetEditable.
  By default a TCanvas is editable.
  By default a TDialogCanvas is not editable.
  TButtons are in general placed in a TDialogCanvas.

  A TButton being a TPad, one can draw graphics primitives in it
  when the TCanvas/TDialogCanvas is editable.

       Example of a macro creating a dialogcanvas with buttons
void but() {
   example of a dialogcanvas with a few buttons

   TDialogCanvas *dialog = new TDialogCanvas("dialog","",200,300);

 Create first button. Clicking on this button will execute 34+56
   TButton *but1 = new TButton("button1","34+56",.05,.8,.45,.88);
   but1->Draw();

 Create second button. Clicking on this button will create a new canvas
   TButton *but2 = new TButton("canvas","c2 = new TCanvas(\"c2\")",.55,.8,.95,.88);
   but2->Draw();

 Create third button. Clicking on this button will invoke the browser
   but3 = new TButton("Browser","br = new TBrowser(\"br\")",0.25,0.54,0.75,0.64);
   but3->SetFillColor(42);
   but3->Draw();

 Create last button with no name. Instead a graph is draw inside the button
 Clicking on this button will invoke the macro $ROOTSYS/tutorials/graphs/graph.C
   button = new TButton("",".x tutorials/graphs/graph.C",0.15,0.15,0.85,0.38);
   button->SetFillColor(42);
   button->Draw();
   button->SetEditable(kTRUE);
   button->cd();

   Double_t x[8] = {0.08,0.21,0.34,0.48,0.61,0.7,0.81,0.92};
   Double_t y[8] = {0.2,0.65,0.4,0.34,0.24,0.43,0.75,0.52};
   TGraph *graph = new TGraph(8,x,y);
   graph->SetMarkerColor(4);
   graph->SetMarkerStyle(21);
   graph->Draw("lp");

   dialog->cd();
}

   Executing the macro above produces the following dialogcanvas