-->Cannot show the Greek letters correctly (press help to see the problem)
You can save your sourcecode with your local codingpage, ISO-8859-7
and you can use the g_convert function to encode the Greek letters to
the UTF-8. The result looks .:
...
var
  text   : PGChar;
  dialog : PGtkWidget;
begin
  text := g_convert ('η απόσταση του  κάθε νέου σημείου από την κορυφή σε',
              70, 'UTF-8', 'ISO-8859-7', NULL, NULL, NULL);
  dialog := gtk_message_dialog_new (GTK_WINDOW (foablak), 0,
              GTK_MESSAGE_INFO, GTK_BUTTONS_CLOSE,
              text);
...

--> when the drawing has been done, if the user move a window over the drawing he will erase it.
I don't know the exactly answer, but maybe you should create this part as in the scribble_simple.pas

Best regards,
Mihaly