books

assets/draw/p02/s06.dart

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+import 'dart:async';
+import 'dart:typed_data';
+
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'dart:ui' as ui;
+
+import 'package:flutter/services.dart';
+
+class Paper extends StatefulWidget {
+  const Paper({super.key});
+
+  @override
+  _PaperState createState() => _PaperState();
+}
+
+class _PaperState extends State<Paper> {
+  ui.Image? _img;
+  bool get hasImage => _img != null;
+
+  @override
+  void initState() {
+    _loadImage();
+    super.initState();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      child: hasImage
+          ? CustomPaint(
+        painter: ImageShaderPainter(_img),
+      )
+          : Container(),
+    );
+  }
+
+  void _loadImage() async {
+    _img = await loadImage(AssetImage('assets/images/wy_200x300.jpg'));
+    setState(() {});
+  }
+
+  late ImageStreamListener listener;
+  //异步加载图片成为ui.Image
+  Future<ui.Image> loadImage(ImageProvider provider) {
+    Completer<ui.Image> completer = Completer<ui.Image>();
+    ImageStream stream = provider.resolve(ImageConfiguration());
+    listener = ImageStreamListener((info, syno) {
+      final ui.Image image = info.image; //监听图片流，获取图片
+      completer.complete(image);
+      stream.removeListener(listener);
+    });
+    stream.addListener(listener);
+    return completer.future;
+  }
+}
+
+class ImageShaderPainter extends CustomPainter {
+  ui.Image? img;
+  late Paint _paint;
+
+  ImageShaderPainter(this.img) {
+    _paint = Paint();
+  }
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    if(img==null) return;
+    _paint.shader = ImageShader(
+        img!,
+        TileMode.repeated,
+        TileMode.repeated,
+        Float64List.fromList([
+          1, 0, 0, 0,
+          0, 1, 0, 0,
+          0, 0, 1, 0,
+          0, 0, 0, 1,
+        ]));
+
+    canvas.drawCircle(Offset(100, 100), 50, _paint);
+    canvas.drawCircle(
+        Offset(100 + 120.0, 100),
+        50,
+        _paint
+          ..strokeWidth = 10
+          ..style = PaintingStyle.stroke);
+    canvas.drawLine(
+        Offset(100 + 120.0 * 2, 50),
+        Offset(100 + 120.0 * 2, 50 + 100.0),
+        _paint
+          ..strokeWidth = 30
+          ..style = PaintingStyle.stroke);
+  }
+
+  @override
+  bool shouldRepaint(CustomPainter oldDelegate) => true;
+}