title: Why does a BoxDecoration increase GestureDetector's area of effect?
body: <p>With the following code, the GestureDetector is only registering taps in the upper left corner of the image.</p>
  
  <pre><code>class _MyHomePageState extends State&lt;MyHomePage&gt; {
  
    void tap(TapDownDetails details) {
      print('${details.globalPosition}');
    }
  
    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: new AppBar(
          title: new Text(widget.title),
        ),
        body: new GestureDetector(
          onTapDown: tap,
          child: new Center(
            child: new Container(
              height: 400.0,
              width: 400.0,
              child: new FittedBox(
                fit: BoxFit.fill,
                child: new Image.asset('assets/900px-image.png'),
              ),
            ),
          ),
        ),
      );
    }
  }
  </code></pre>
  
  <p>I would like it to register taps anywhere in the box containing the Image.  However, I did discover that if I add a BoxDecoration to the Container containing the Image, it does register taps anywhere in the box.  How does GestureDetector determine its area of effect and why does the BoxDecoration change it?</p>
  
  <pre><code>  body: new GestureDetector(
      onTapDown: tap,
      child: new Center(
        child: new Container(
          height: 400.0,
          width: 400.0,
          decoration: new BoxDecoration(color: Colors.transparent),
          child: new FittedBox(
            fit: BoxFit.fill,
            child: new Image.asset('assets/900px-image.png'),
          ),
        ),
      ),
    ),
  </code></pre>