Flutter Web, toByteData, await never returns
toByteData doesn't work for Flutter web on beta channel yet.So workaround is to use html canvas to generate image.
import 'package:universal_html/html.dart' as html;final htmlCanvas = html.CanvasElement(width: size.width.floor(), height: size.height.floor());final html.CanvasRenderingContext2D context = htmlCanvas.getContext("2d");context.fillStyle = 'white';context.fillRect(0, 0, size.width, size.height);for (int i = 0 ; i < _paths.length ; i++) { context.strokeStyle = 'red'; context.lineWidth = _paths[i].key.strokeWidth; context.beginPath(); context.moveTo(caculatedOffset.dx, caculatedOffset.dy); for (int j = 1 ; j < _paths[i].value.length ; j ++) { context.lineTo(caculatedOffset.dx, caculatedOffset.dy); } context.stroke();}final blob = await htmlCanvas.toBlob('image/jpeg', 0.8);