portion of default_app_bar.dart

default_app_bar.dart

// add SingleTickerProviderStateMixin to our State widget
class _DefaultAppBarState extends State<DefaultAppBar> with SingleTickerProviderStateMixin {
}

// intialize animation and controller
AnimationController _controller;
Animation _animation;

@override
initState() {
  super.initState();

  _controller = AnimationController(vsync: this, duration: Duration(milliseconds: 800));
  _animation = Tween(begin: 0.0, end: 1.0).animate(_controller);
}

//we'll run the animation in forward direction when user taps on search icon
void onSearchTapUp(TapUpDetails details) {
  setState(() {
    rippleStartX = details.globalPosition.dx;
    rippleStartY = details.globalPosition.dy;
  });

  print("pointer location $rippleStartX, $rippleStartY");
  
  // run animation controller in forward direction
  // as we now have center point for ripple animation
  _controller.forward();
}

// lastly we'll add AnimationBuilder which uses our MyPainter and AnimationController to render ripple animation
AnimatedBuilder(
  animation: _animation,
  builder: (context, child) {
    return CustomPaint(
      painter: MyPainter(
        containerHeight: widget.preferredSize.height,
        center: Offset(rippleStartX ?? 0, rippleStartY ?? 0),
        // increase radius in % from 0% to 100% of screenWidth
        radius: _animation.value * screenWidth,
        context: context,
      ),
    );
  },
),