50x50 circle button centered on screen with bad touch area

bad_touch_area.dart

// At center of screen...
new FractionalTranslation(
  translation: const Offset(0.5, 0.5),

  // Stack whose origin is centered on screen
  child: new Stack(
    children: <Widget>[
      // This FractionalTranslation pulls the button back by
      // 50% in both directions to center the button at the
      // Stack's origin
      new FractionalTranslation(
        translation: const Offset(-0.5, -0.5),

        // 50x50 circle button with search icon that is centered
        // on screen, but the touch area only exists in the lower
        // right quadrant of the button.  I think this is because
        // the button is moved 50% to the top and left of the
        // Stack's positive coordinate system.  In other words,
        // the button is 50% to the top and left of the Stack's
        // origin.  So I'm guessing that the Stack is suppressing
        // that touch area.
        child: new Container(
          width: 50.0,
          height: 50.0,
          child: new RawMaterialButton(
            shape: new CircleBorder(),
            fillColor: Colors.purple,
            child: new Icon(
              Icons.search,
              color: Colors.white,
            ),
            onPressed: () {
              print('Pressed');
            },
          ),
        ),
      ),
    ],
  )
),