books

assets/draw/p03/s02.dart

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+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.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 Container(
+      color: Colors.white,
+      child: CustomPaint(
+        // 使用CustomPaint
+        painter: PaperPainter(),
+      ),
+    );
+  }
+}
+
+class PaperPainter extends CustomPainter {
+  late Paint _gridPint; // 画笔
+  final double step = 20; // 小格边长
+  final double strokeWidth = .5; // 线宽
+  final Color color = Colors.grey; // 线颜色
+
+  PaperPainter() {
+    _gridPint = Paint()
+      ..style = PaintingStyle.stroke
+      ..strokeWidth = strokeWidth
+      ..color = color;
+  }
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    canvas.translate(size.width / 2, size.height / 2);
+    _drawGrid(canvas, size);
+    _drawPart(canvas);
+  }
+
+  void _drawPart(Canvas canvas) {
+    var paint = Paint()
+      ..style = PaintingStyle.fill
+      ..color = Colors.blue;
+    canvas.drawCircle(Offset(0, 0), 50, paint);
+    canvas.drawLine(
+        Offset(20, 20),
+        Offset(50, 50),
+        paint
+          ..color = Colors.red
+          ..strokeWidth = 5
+          ..strokeCap = StrokeCap.round
+          ..style = PaintingStyle.stroke);
+  }
+
+  void _drawGrid(Canvas canvas, Size size) {
+    _drawBottomRight(canvas, size);
+
+    canvas.save();
+    canvas.scale(1, -1); //沿x轴镜像
+    _drawBottomRight(canvas, size);
+    canvas.restore();
+
+    canvas.save();
+    canvas.scale(-1, 1); //沿y轴镜像
+    _drawBottomRight(canvas, size);
+    canvas.restore();
+
+    canvas.save();
+    canvas.scale(-1, -1); //沿原点镜像
+    _drawBottomRight(canvas, size);
+    canvas.restore();
+  }
+
+  void _drawBottomRight(Canvas canvas, Size size) {
+    canvas.save();
+    for (int i = 0; i < size.height / 2 / step; i++) {
+      canvas.drawLine(Offset(0, 0), Offset(size.width / 2, 0), _gridPint);
+      canvas.translate(0, step);
+    }
+    canvas.restore();
+
+    canvas.save();
+    for (int i = 0; i < size.width / 2 / step; i++) {
+      canvas.drawLine(Offset(0, 0), Offset(0, size.height / 2), _gridPint);
+      canvas.translate(step , 0);
+    }
+    canvas.restore();
+  }
+
+  @override
+  bool shouldRepaint(CustomPainter oldDelegate) => true;
+}