title: Flutter GestureDetector: How to pinch in/out or zoom in/out Text using two fingers?
body: <p>I'm creating a text field like Text or RichText. And after that, I want to zoom in/out the size of text using pinching. For now, I tried implementing <code>GestureDetector</code> but it zooms in/out with one finger too. And it is really hard to aim pinching detection. Sometimes is freezing. I added a video that shows when after pinching it freezes and suddenly get bigger. The second video is with the case that image zoom in only when I tap on the text with one finger and move to up left corner. The ideal implementation is to detect pinch and zoom in/out all text area. And disable zooming when I use only one finger. Could you send me some hints, link or code how to solve or where to find the solution?</p>
  
  <p><img src="https://i.stack.imgur.com/a5AOV.gif" width="300">
  <img src="https://i.stack.imgur.com/VP9Oa.gif" width="300"></p>
  
  <pre class="lang-dart prettyprint-override"><code>body: GestureDetector(
    onScaleUpdate: (details) {
      setState(() {
        _textSize =
            _initTextSize + (_initTextSize * (details.scale * .35));
      });
    },
    onScaleEnd: (ScaleEndDetails details) {
      setState(() {
        _initTextSize = _textSize;
      });
    },
    child: Center(
        child: SizedBox(
      height: _textSize,
      child: FittedBox(
        child: Text("Test"),
      ),
    ))),
  </code></pre>