Flutter 实现酷炫的3D效果示例代码

此文讲解3个酷炫的3D动画效果。

下面是要实现的效果：

Flutter 中3D效果是通过 Transform 组件实现的，没有变换效果的实现：

class TransformDemo extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
 return Scaffold(
 appBar: AppBar(
 title: Text('3D 变换Demo'),
 ),
 body: Container(
 alignment: Alignment.center,
 color: Colors.white,
 child: Text('3D 变换Demo'),
 ),
 );
 }
}

通过 GestureDetector 组件添加滑动事件监听：

@override
Widget build(BuildContext context) {
 return Scaffold(
 appBar: AppBar(
 title: Text('3D 变换Demo'),
 ),
 body: GestureDetector(
 onPanUpdate: (details) {
 print('$details');
 },
 child: Container(
 alignment: Alignment.center,
 color: Colors.white,
 child: Text('3D 变换Demo'),
 ),
 ),
 );
}

添加 Transform 对组件进入旋转：

@override
Widget build(BuildContext context) {
 return Transform(
 transform: Matrix4.identity()
 ..setEntry(3, 2, 0.001)
 ..rotateX(pi/6)
 ..rotateY(pi/6),
 alignment: Alignment.center,
 child: Scaffold(
 appBar: AppBar(
  title: Text('3D 变换Demo'),
 ),
 body: GestureDetector(
  onPanUpdate: (details) {
  },
  child: Container(
  alignment: Alignment.center,
  color: Colors.white,
  child: Text('3D 变换Demo'),
  ),
 ),
 ));
}

将滑动的偏移和旋转进行关联：

class TransformDemo extends StatefulWidget {
 @override
 _TransformDemoState createState() => _TransformDemoState();
}

class _TransformDemoState extends State<TransformDemo> {
 double _rotateX = .0;
 double _rotateY = .0;

 @override
 Widget build(BuildContext context) {
 return Transform(
 transform: Matrix4.identity()
  ..rotateX(_rotateX)
  ..rotateY(_rotateY),
 alignment: Alignment.center,
 child: Scaffold(
  appBar: AppBar(
  title: Text('3D 变换Demo'),
  ),
  body: GestureDetector(
  onPanUpdate: (details) {
  setState(() {
  _rotateX += details.delta.dy * .01;
  _rotateY += details.delta.dx * -.01;
  });
  },
  child: Container(
  alignment: Alignment.center,
  color: Colors.white,
  child: Text('3D 变换Demo'),
  ),
  ),
 ));
 }
}

基本已经实现了3D效果，但效果比较生硬，尤其垂直方向旋转的时候远点和近点在屏幕上的宽度是一样，

添加近大远小的效果：

Transform(
 transform: Matrix4.identity()
 ..setEntry(3, 2, 0.001)
 ..rotateX(_rotateX)
 ..rotateY(_rotateY),
 ...

翻书效果

上面的效果类似于翻书的效果。

实现的原理：

将图片左右切割为两部分，两张图片共分割为4个新的组件，如下图，分别为1、2、3、4

代码实现：

_child1 = ClipRect(
 child: Align(
 alignment: Alignment.centerLeft,
 widthFactor: 0.5,
 child: child1,
 ),
);
_child2 = ClipRect(
 child: Align(
 alignment: Alignment.centerRight,
 widthFactor: 0.5,
 child: child1,
 ),
);

_child3 = ClipRect(
 child: Align(
 alignment: Alignment.centerLeft,
 widthFactor: 0.5,
 child: child2,
 ),
);

_child4 = ClipRect(
 child: Align(
 alignment: Alignment.centerRight,
 widthFactor: 0.5,
 child: child2,
 ),
);

将第一张图片放在第二种图片的上面，先旋转 组件2 从 0度到 90度，然后再旋转 组件3 从 -90度到0度，代码实现：

Row(
 mainAxisAlignment: MainAxisAlignment.center,
 children: <Widget>[
 Stack(
 children: [
 _child1,
 Transform(
  alignment: Alignment.centerRight,
  transform: Matrix4.identity()
  ..setEntry(3, 2, 0.001)
  ..rotateY(_animation1.value),
  child: _child3,
 ),
 ],
 ),
 Container(
 width: 3,
 color: Colors.white,
 ),
 Stack(
 children: [
 _child4,
 Transform(
  alignment: Alignment.centerLeft,
  transform: Matrix4.identity()
  ..setEntry(3, 2, 0.001)
  ..rotateY(_animation.value),
  child: _child2,
 )
 ],
 )
 ],
)

动画控制器设置：

@override
void initState() {
 init();
 _controller =
 AnimationController(vsync: this, duration: Duration(seconds: 5))
 ..addListener(() {
  setState(() {});
 });
 _animation = Tween(begin: .0, end: pi / 2)
 .animate(CurvedAnimation(parent: _controller, curve: Interval(.0, .5)));
 _animation1 = Tween(begin: -pi / 2, end: 0.0).animate(
 CurvedAnimation(parent: _controller, curve: Interval(.5, 1.0)));
 _controller.forward();
 super.initState();
}

其中 child1, child2为两种图片，代码如下：

_FlipUpDemoState(
 Container(
 width: 300,
 height: 400,
 child: Image.asset(
 'assets/images/b.jpg',
 fit: BoxFit.cover,
 ),
 ),
 Container(
 width: 300,
 height: 400,
 child: Image.asset(
 'assets/images/c.jpeg',
 fit: BoxFit.cover,
 ),
 ))

最后生成的效果就是开始的翻书效果。

上面是左右翻页效果，同理换成上下翻页效果：

@override
Widget build(BuildContext context) {
 return Scaffold(
 appBar: AppBar(),
 body: Column(
 mainAxisAlignment: MainAxisAlignment.center,
 children: <Widget>[
 Stack(
  children: [
  _upperChild1,
  Transform(
  alignment: Alignment.bottomCenter,
  transform: Matrix4.identity()
  ..setEntry(3, 2, 0.003)
  ..rotateX(_animation1.value),
  child: _upperChild2,
  ),
  ],
 ),
 SizedBox(
  height: 2,
 ),
 Stack(
  children: [
  _lowerChild2,
  Transform(
  alignment: Alignment.topCenter,
  transform: Matrix4.identity()
  ..setEntry(3, 2, 0.003)
  ..rotateX(_animation.value),
  child: _lowerChild1,
  )
  ],
 )
 ],
 ),
 );
}