books

packages/idraw/lib/p12/s02.dart

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+import 'dart:math';
+import 'dart:ui';
+import 'package:flutter/material.dart';
+
+import '../components/coordinate_pro.dart';
+/// create by 张风捷特烈 on 2020-03-19
+/// contact me by email 1981462002@qq.com
+/// 说明: 纸
+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, this.handleRadius = 20.0})
+      : super(key: key);
+
+  @override
+  _HandleWidgetState createState() => _HandleWidgetState();
+}
+
+class _HandleWidgetState extends State<HandleWidget> {
+  ValueNotifier<Offset> _offset = ValueNotifier(Offset.zero);
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+        onPanEnd: reset,
+        onPanUpdate: parser,
+        child: CustomPaint(
+            size: Size(widget.size, widget.size),
+            painter: _HandlePainter(
+                color: Colors.green,
+                handleR: widget.handleRadius,
+                offset: _offset)));
+  }
+
+  reset(DragEndDetails details) {
+    _offset.value = Offset.zero;
+  }
+
+  parser(DragUpdateDetails details) {
+    final offset = details.localPosition;
+    double dx = 0.0;
+    double dy = 0.0;
+
+    dx = offset.dx - widget.size / 2;
+    dy = offset.dy - widget.size / 2;
+    var rad = atan2(dx, dy);
+    if (dx < 0) {
+      rad += 2 * pi;
+    }
+    var bgR = widget.size / 2 - widget.handleRadius;
+    var thta = rad - pi / 2; //旋转坐标系90度
+    if (sqrt(dx * dx + dy * dy) > bgR) {
+      dx = bgR * cos(thta);
+      dy = -bgR * sin(thta);
+    }
+    _offset.value = Offset(dx, dy);
+  }
+}
+
+class _HandlePainter extends CustomPainter {
+  final _paint = Paint();
+  final ValueNotifier<Offset> offset;
+  final Color color;
+
+  var handleR;
+
+  _HandlePainter({this.handleR,required this.offset, this.color = Colors.blue})
+      : super(repaint: offset) ;
+
+  @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.style = PaintingStyle.fill;
+    _paint.color = color.withAlpha(100);
+
+    canvas.drawCircle(Offset(0, 0), bgR, _paint);
+
+    _paint.color = color.withAlpha(150);
+
+    canvas.drawCircle(
+        Offset(offset.value.dx, offset.value.dy), handleR, _paint);
+
+    _paint.color = color;
+    _paint.style = PaintingStyle.stroke;
+    canvas.drawLine(Offset.zero, offset.value, _paint);
+  }
+
+  @override
+  bool shouldRepaint(_HandlePainter oldDelegate) =>
+      oldDelegate.offset != offset ||
+          oldDelegate.color != color ||
+          oldDelegate.handleR != handleR;
+}