问在颤动中将RadialGradient中心定位在绝对位置(以像素为单位)

EN

import 'package:flutter/material.dart';

    void main() {
      runApp(MyApp());
    }
    
    class MyApp extends StatefulWidget {
      @override
      _MyAppState createState() => _MyAppState();
    }
    
    class _MyAppState extends State with TickerProviderStateMixin{
      @override
      Widget build(BuildContext context) {
        return Container(
          decoration: BoxDecoration(
              gradient: RadialGradient(
                colors: [Colors.white, Colors.blueAccent],
                center: Alignment(0,-0.5), // I want to input absolute position in pixels here!
              )
          ),
        );
      }
    }