CLASS Greeter
  PUBLIC:
    ' This object owns the window's small piece of application state.
    X AS INTEGER
    Y AS INTEGER
    Moving AS INTEGER
    ' The last whole TIMER second painted; -1 requests the initial/final paint.
    LastSecond AS SINGLE
    DECLARE CONSTRUCTOR ()
    DECLARE SUB Paint ()
END CLASS

' The window callbacks share one Greeter instance for this application's life.
DIM SHARED App AS Greeter

CONSTRUCTOR Greeter ()
  THIS.X = 104
  THIS.Y = 112
  THIS.Moving = -1
  THIS.LastSecond = -1!
END CONSTRUCTOR

SUB Greeter.Paint ()
  DIM Now AS SINGLE

  ' TIMER is sampled by d/OS; INT makes the animation exactly once per second.
  Now = INT(TIMER)
  IF Now <> THIS.LastSecond THEN
    THIS.LastSecond = Now
    ' RND is deterministic here: the sample does not seed it from wall time.
    IF THIS.Moving <> 0 THEN
      ' Keep the native 6x10 greeting inside the portable 320x192 surface.
      THIS.X = INT(RND(1) * 241)
      THIS.Y = INT(RND(1) * 183)
    END IF
    ' A complete GFX Intent frame: clear, draw text, then make it visible.
    INTENT GFX.BEGIN_FRAME()
    INTENT GFX.FILL_RECT(0, 0, 320, 192, 2081)
    INTENT GFX.DRAW_TEXT(THIS.X, THIS.Y, "HELLO, WORLD!", 3, -1, 2081)
    INTENT GFX.PRESENT()
  END IF
  IF THIS.Moving <> 0 THEN
    ' Keep DRAW owed so the dispatcher can sample queued KEY/CLOSE events.
    SERVICE INVALIDATE()
  END IF
END SUB

' OPEN creates the application's object and gives the window its initial title.
WINDOW SUB OPEN()
  SERVICE SET_TITLE("Hello, world! Press any key.")
  App = NEW Greeter()
END SUB

' DRAW delegates presentation to the object that owns the state.
WINDOW SUB DRAW()
  App.Paint
END SUB

' CLOSE releases that object deterministically.
WINDOW SUB CLOSE()
  App = NOTHING
END SUB

' Any key stops new positions, asks for one final paint, and leaves the window open.
ON KEY SUB (K AS INTEGER)
  App.Moving = 0
  App.LastSecond = -1!
  SERVICE SET_TITLE("Stopped")
  SERVICE INVALIDATE()
END SUB