在图像上方添加文本并调整大小

Question

我正在尝试编写一个使用图像URL的函数，并在图像顶部添加文本，然后共享它。

现在，我在三个位置添加文本。中间有一个段落，段落下方是作者的名字，图像的右下角有一些文字。一切工作正常，除了我似乎无法将图像调整为合适的大小。如何将以下内容调整为500px x 500px以便共享？

任何帮助将不胜感激。

import 'dart:io';
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter/services.dart';
import 'package:esys_flutter_share/esys_flutter_share.dart'; 
import 'package:image/image.dart' as nImg; 

tryThis() async{
    var uri = Uri.parse([IMAGE URL]);
    var httpClient = HttpClient();
    var request = await httpClient.getUrl(uri);
    var response = await request.close();
    var imageData = <int>[];
    await response.forEach((data) async {
      imageData.addAll(data);
    });
    ui.Image image =
        await decodeImageFromList(Uint8List.fromList(imageData));
    var pictureRecorder = ui.PictureRecorder();
    var canvas = Canvas(pictureRecorder);
    var paint = Paint();
    paint.isAntiAlias = true;
    var src = Rect.fromLTWH(
        0.0, 0.0, image.width.toDouble(), image.height.toDouble());
    var dst = Rect.fromLTWH(
        0.0, 0.0, image.width.toDouble(), image.height.toDouble());
    canvas.drawRect(Rect.fromLTWH(0.0, 0.0, 100.0, 100.0), paint);
    canvas.drawImageRect(image, src, dst, paint);


    //Add text on image
    TextSpan span = new TextSpan(
        style: new TextStyle(color: Colors.white, fontSize: 50.0,
            fontFamily: 'Roboto'), text: "Main text description with padding");
    TextSpan nextSpan = new TextSpan(
        style: new TextStyle(color: Colors.white, fontSize: 50.0,
            fontFamily: 'Roboto'), text: "Secondary text underneath");

    TextPainter tp = new TextPainter(
        text: span, textDirection: prefix0.TextDirection.ltr, textAlign: TextAlign.center,  textWidthBasis: TextWidthBasis.parent);
    TextPainter tpNext = new TextPainter(
        text: nextSpan, textDirection: prefix0.TextDirection.ltr, textAlign: TextAlign.right,  textWidthBasis: TextWidthBasis.parent);

    var imgMaxSpace = image.width.toDouble()-35;
    tp.layout(maxWidth: imgMaxSpace);
    tpNext.layout(maxWidth: imgMaxSpace);
    tp.paint(canvas, new Offset(20, image.height/5));
    tpNext.paint(canvas, new Offset(image.width-tpNext.width - 50, image.height/5+tp.height));

    //Add logo text on bottom of image
    TextSpan bottomtxt = new TextSpan(
        style: new TextStyle(color: Colors.white, fontSize: 50.0,
            fontFamily: 'Roboto'), text: "Logo text");
    TextPainter ltp = new TextPainter(
        text: bottomtxt, textDirection: prefix0.TextDirection.ltr,  textAlign: TextAlign.center,  textWidthBasis: TextWidthBasis.parent);
    var newWidth = image.width.toDouble() - 25;

    ltp.layout();
    ltp.paint(canvas, new Offset(newWidth-ltp.width, image.height.toDouble()-75));


    var pic = pictureRecorder.endRecording();
    ui.Image img = await pic.toImage(image.width, image.height);
    var byteData = await img.toByteData(format: ui.ImageByteFormat.png);
    var buffer = byteData.buffer.asUint8List();


    //SHARE IMAGE WHEREVER
    await Share.file('esys image', 'esys.png', buffer, 'image/png');

  }