books

assets/draw/p07/s02.dart

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+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 Container(
+      color: Colors.white,
+      child: CustomPaint(
+        // 使用CustomPaint
+        painter: PaperPainter(),
+      ),
+    );
+  }
+}
+
+class PaperPainter extends CustomPainter {
+  static const double step = 15; // 方格变长
+  final Coordinate coordinate = Coordinate(step: step);
+
+  // 颜色列表 256 个元素
+  final List<Color> colors =
+  List<Color>.generate(256, (i) => Color.fromARGB(255 - i, 255, 0, 0));
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    Paint paint = Paint();
+
+    canvas.save();
+    canvas.translate(size.width / 2, size.height / 2);
+
+    // 遍历列表 绘制矩形色块
+    canvas.translate(-step * 8.0, -step * 8.0);
+    colors.asMap().forEach((i, color) {
+      int line = (i % 16); // 行
+      int row = i ~/ 16; // 列
+      var topLeft = Offset(step * line, step * row);
+      var rect = Rect.fromPoints(topLeft, topLeft.translate(step, step));
+      canvas.drawRect(rect, paint..color = color);
+    });
+
+    canvas.restore();
+    coordinate.paint(canvas, size); //绘制坐标系
+  }
+
+  @override
+  bool shouldRepaint(CustomPainter oldDelegate) => false;
+}