InteractiveViewer image is zoomed in

Question

My problem should be simple, but i'm stuck: i need to display the image of a map with a marker over it (that's why i'm using a stack) and this image can be zoomed and panned. The only problem is, when i open the app the image is totally zoomed in, and i have to zoom out manually. I tried reading the docs and googling but i only found libraries which don't suit my needs or don't work as expected.

So, the question is simple: how can i see the fully zoomed out image from the beginning?

Here's the code.

    return Container(
      height: 350,
      child: InteractiveViewer(
        // TODO the image is automatically zoomed in!
        minScale: .1,
        maxScale: 1,
        constrained: false,
        child: Stack(children: [
          Image.asset(itinerary.mapImage, fit: BoxFit.fitWidth),
          icon(...),
        ])
      )
    )

Answer 1

You need to use a TransformationController to control InteractiveViewer. Here is the code:

  TransformationController _controller;

  @override
  void initState() {
    _controller = TransformationController();
    _controller.value = Matrix4.identity() * 0.5;
    super.initState();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Container(
        height: 350,
        child: InteractiveViewer(
          transformationController: _controller,
          minScale: .1,
          maxScale: 1,
          onInteractionEnd: (s) {
            print(_controller.value);
          },
          constrained: false,
          child: Stack(
            children: [
              Image.asset(
                "assets/Big.Buck.Bunny.-.Landscape.png",
                fit: BoxFit.fitWidth,
              ),
            ],
          ),
        ),
      ),
    );
  }

Please note that you may need to adjust initial scale value(the one multiplying with Matrix4) to get your desired output.