books

packages/idraw/lib/p12/s01.dart

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+import 'package:flutter/material.dart';
+
+/// create by 张风捷特烈 on 2020/11/3
+/// contact me by email 1981462002@qq.com
+/// 说明:
+
+class Paper extends StatelessWidget {
+  const Paper({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Center(
+      child: HandleWidget(),
+    );
+  }
+}
+
+class HandleWidget extends StatefulWidget {
+  final double size;
+  final double handleRadius;
+
+  HandleWidget({Key? key, this.size = 160.0, this.handleRadius = 20.0})
+      : super(key: key);
+
+  @override
+  _HandleWidgetState createState() => _HandleWidgetState();
+}
+
+class _HandleWidgetState extends State<HandleWidget> {
+  @override
+  Widget build(BuildContext context) {
+    return CustomPaint(
+        size: Size(widget.size, widget.size),
+        painter: _HandlePainter(handleR: widget.handleRadius));
+  }
+}
+
+class _HandlePainter extends CustomPainter {
+  var _paint = Paint();
+
+  var handleR;
+
+  _HandlePainter({this.handleR}) {
+    _paint
+      ..color = Colors.blue
+      ..style = PaintingStyle.fill
+      ..isAntiAlias = true;
+  }
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    canvas.clipRect(Offset.zero & size);
+
+    final bgR = size.width / 2 - handleR;
+
+    canvas.translate(size.width / 2, size.height / 2);
+    _paint.color = _paint.color.withAlpha(100);
+    canvas.drawCircle(Offset(0, 0), bgR, _paint);
+    _paint.color = _paint.color.withAlpha(150);
+    canvas.drawCircle(Offset(0, 0), handleR, _paint);
+  }
+
+  @override
+  bool shouldRepaint(_HandlePainter oldDelegate) =>
+      oldDelegate.handleR != handleR;
+}