Gradient stuff

main.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:ui' as ui;
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(child: CustomPaint(
      painter: FooPainter(),
      size: const Size(400, 400)
   ));
  }
}


class FooPainter extends CustomPainter {

  @override
  void paint(Canvas canvas, Size size) {
    canvas.drawRect(Rect.fromLTWH(0, 0, size.width, size.height), Paint()
      ..shader = ui.Gradient.linear(
        const Offset(25, 25),
        Offset(size.width - 25, size.height - 25),
        <Color>[Colors.red, Colors.blue],
        [0, 1.0],
        TileMode.decal,
      )
      // Try changing or removing blend mode
      ..colorFilter = ui.ColorFilter.mode(Colors.orange, BlendMode.src)
    );
    canvas.drawRect(Rect.fromLTWH(0, 0, size.width, size.height), Paint()..color = Colors.green ..style = PaintingStyle.stroke);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return true;
  }
}