CONST Duration = 10;

PROC EqTri(a, b) IS 
  IF 
    VAR c ~ (0.4, 1) REL (a, b) IN 
      (a, b) CONG (b, c) AND 
      (b, c) CONG (c, a) -> 
        PS.MoveTo(a); 
        PS.LineTo(b); 
        PS.LineTo(c); 
        PS.Close(); 
        PS.Fill() 
    END 
  FI 
END;

UI PointTool(EqTri);

PROC TriAtT(a, b, c, t) IS 
  VAR 
    theta = Math.Pi * 2 * t, 
    p = (COS(theta), SIN(theta)) 
  IN 
    EqTri(a, p REL (c, b)) 
  END 
END;

PROC Go(a, b, c) IS 
  Anim.Play((CLOSE(TriAtT, a, b, c), Duration)) 
END;

UI PointTool(Go);

PROC Cmd0() IS 
  IF 
    VAR 
      a = (64.38, 238.2), 
      b = (178.7, 288.2), 
      c = (202.2, 198) 
    IN 
      Go(a, b, c); PS.Reset() 
    END 
  FI 
END;