Flutter PointerEvent vs OnTap, one works, the other doesn't - flutter

Question

I have a stack widget I am trying to create in which:
1. The user touches the widget button triggering a pointerDown event.
2. Pointer down causes a slider type widget to scale from 0 to 100% from behind the button
3. With finger still down, the user drags to select a value on the scale
4. The value is selected by releasing the finger from the screen i.e. pointerUp.
The widget works fine when I use onTap instead of pointerDown in step 1. But when I try to use a pointer down event, the _open method (that manages the scaleUp of the slider) isn't triggered.
I have followed this example almost exactly: https://fireship.io/lessons/flutter-radial-menu-staggered-animations/, but have tried to change the touch event on the floatingActionbuton like this:
Transform.scale(
scale: widget.scale.value,
child: Listener(
onPointerDown: (PointerDownEvent event) {
print('pointer is down');
setState(() {
_open;
});
},
child: FloatingActionButton(child: Icon(Icons.blur_circular), onPressed: () {})),
)
The print part detects and fires the event, but the _open method does not do anything and the menu part does not appear like in the tutorial link.
I am at a loss.

Answer 1

Since the button below the FloatingActionButton also has a listener, The Listener widget doesn't get's the PointerDown event. So to do that you have to change the behaviour to opaque so that both get the events.
Try Something like this:
Listener(
behavior: HitTestBehavior.opaque,
onPointerDown: (PointerDownEvent details){
},
child: ...,
)