Flutter PhotoView - Rotation about the point between the fingers

问题

I am using PhotoView (https://pub.dev/packages/photo_view) to showcase a map saved in gif format. I need the ability to zoom and rotate. My code:

class MapView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return PhotoView(
      imageProvider: AssetImage("assets/maps/my_map.gif"),
      enableRotation: true,
      backgroundDecoration: BoxDecoration(
        color: Colors.white,
      ),
    );
  }
}

The problem is that the picture is rotated relative to the center of the picture, which is inconvenient. I want the rotation to be about a point between the two fingers that perform the rotation gesture (as in normal map applications). I have not found any information in the PhotoView documentation on how to fix this.

I hope for your support.

My final code (using matrix_gesture_detector):

class MapView extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _MapViewState();
}

class _MapViewState extends State<MapView> {
  Matrix4 transform;

  @override
  void initState() {
    super.initState();
    transform = Matrix4.identity();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.white,
      child: MatrixGestureDetector(
        onMatrixUpdate: (m, tm, sm, rm) {
          setState(() {
            transform = m;
          });
        },
        child: Transform(
          transform: transform,
          child: Image.asset("assets/maps/my_map.gif"),
        ),
      ),
    );
  }
}

回答1:

So there isn't anything I could find in Photo View that will help you achieve it, so use this package instead. Matrix gesture detector will work exactly the way you want.

Sample code:

class Test extends StatefulWidget {
@override
_TestState createState() => _TestState();
}

class _TestState extends State<Test> {

 Matrix4 transform;
 @override
 void initState() {
 super.initState();
 transform = Matrix4.identity();
 }

 @override
 Widget build(BuildContext context) {
    return Scaffold(
    body: Container(
       width: MediaQuery.of(context).size.width,
       height: MediaQuery.of(context).size.height,
       child: MatrixGestureDetector(
         onMatrixUpdate: (m, rs, ry, rx){
           setState(() {
             transform = m;
       });
      },
      child: Container(
        transform: transform,
        height: 200,
        width: 200,
        color: Colors.blue,
      ),
    ),
  ),
   );
}

}

You can place whatever you like in the container, in your case decoration Image.

来源：https://stackoverflow.com/questions/63207173/flutter-photoview-rotation-about-the-point-between-the-fingers

标签

Flutter

dart

rotation

gesture