Different behavior when nesting Transform.scale and Transform.translate - flutter

Question

I want to implement scale and translate behavior. I write it in _TransformScaleAndTranslate().
But I got different behavior between
[Transform.translate outside Transform.rotate]
vs
[Transform.rotate outside Transform.translate]
The result shows that if I translate after scale, [Transform.translate outside Transform.rotate] can't translate follow my pointer correctly.
Is there something wrong? or anything I didn't get it?
import 'package:flutter/material.dart';
class Home extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Test1'),
),
body: const _BodyWidget(),
);
}
}
class _BodyWidget extends StatefulWidget {
const _BodyWidget({
Key key,
}) : super(key: key);
#override
__BodyWidgetState createState() => __BodyWidgetState();
}
class __BodyWidgetState extends State<_BodyWidget> {
Offset _startFocalPoint = Offset.zero;
Offset _lastOffset = Offset.zero;
Offset _currentOffset = Offset.zero;
double _lastScale = 1.0;
double _currentScale = 1.0;
#override
Widget build(BuildContext context) {
return GestureDetector(
onScaleStart: _onScaleStart,
onScaleUpdate: _onScaleUpdate,
child: Stack(
fit: StackFit.expand,
children: <Widget>[
_TransformScaleAndTranslate(_currentOffset, _currentScale),
],
),
);
}
void _onScaleStart(ScaleStartDetails details) {
_startFocalPoint = details.focalPoint;
_lastOffset = _currentOffset;
_lastScale = _currentScale;
}
void _onScaleUpdate(ScaleUpdateDetails details) {
if (details.scale != 1.0) {
double currentScale = _lastScale * details.scale;
if (currentScale < 0.5) {
currentScale = 0.5;
}
setState(() {
_currentScale = currentScale;
});
// The place I calculate for translate
} else if (details.scale == 1.0) {
Offset currentOffset =
_lastOffset + (details.focalPoint - _startFocalPoint) / _lastScale;
setState(() {
_currentOffset = currentOffset;
});
}
}
}
class _TransformScaleAndTranslate extends StatelessWidget {
final Offset _currentOffset;
final double _currentScale;
const _TransformScaleAndTranslate(
this._currentOffset,
this._currentScale, {
Key key,
}) : super(key: key);
//Put Transform.translate or Transform.scale outside got different behavior when translate after scaled.
#override
Widget build(BuildContext context) {
return Transform.translate(
offset: _currentOffset,
child: Transform.scale(
scale: _currentScale,
child: Image.asset(
'assets/images/elephant.jpg',
fit: BoxFit.contain,
),
),
);
}
}