How to Continue Transform/Rotation? - Dart/Flutter

Question

I've been having some problems using Transform.Rotate in dart/Flutter. I have set up my code so that I can rotate an image with gestures. However once I've rotated the image once and let go and continue the rotation the image is reset back to its original position.

It's the same issue shown here: Rotation gesture produces undesired rotation

The solution here is to save the transform in a variable. Is there any way to save the transform in a variable in Dart/Flutter?

Also the ideal situation would be that I can animate the rotation a little so it's delayed slightly because right now it responds straight away to rotation. If this part is unclear please let me know!!

Any suggestions are welcome!!!

Answer 1

You basically want to save the state of the widget so I think you will need to wrap it in a StatefulWidget to be able to do that. (https://www.youtube.com/watch?v=AqCMFXEmf3w)

To smooth out the animation you could maybe try and use the AnimatedContainer? I haven't used it myself but I think it should be what you need! (https://www.youtube.com/watch?v=yI-8QHpGIP4)

EDIT

Okay, I've got it working for you.

Offset vector;
  double startingAngle;
  double deltaAngle = 0.0;
  double finalAngle = 0.0;
  // store the final angle of the object
  double finalObjectAngle = 0.0;


  void _onPanStart(DragStartDetails details) {
    _polarCoordFromGlobalOffset(details.globalPosition);
    startingAngle = vector.direction;
    print('START = $startingAngle ===================================');
  }

  void _onPanUpdate(DragUpdateDetails details) {
    _polarCoordFromGlobalOffset(details.globalPosition);

    setState(() {
      // HERE you should use the finalObjectAngle
      deltaAngle = vector.direction - startingAngle + finalObjectAngle;
      finalAngle = deltaAngle;
    });
  }

  void _onPanEnd(DragEndDetails details) {
    finalAngle = deltaAngle;
    // Save the finalAngle of the object
    finalObjectAngle = finalAngle;
    print('End = $finalAngle ===================================');
  }