Sample app of CustomPaint not setting isComplex

main.dart

import 'package:flutter/material.dart';

final imageUrl =
    'https://cdn.vox-cdn.com/thumbor/yacVJaRnOvWiuIO3L6pe5Tmlv68=/0x26:640x453/920x613/filters:focal(0x26:640x453):format(webp)/cdn.vox-cdn.com/assets/1275052/kitten_field_jump.jpeg';

class CostlyToRasterize extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    const color = Color(0xff00ff);
    return Stack(
      children: [
        Image.network(imageUrl),
        Container(
          decoration: BoxDecoration(
            gradient: LinearGradient(
              begin: Alignment(0, 0.5),
              end: Alignment.bottomCenter,
              colors: [color.withOpacity(0), color.withOpacity(0.9)],
            ),
          ),
        ),
      ],
    );
  }
}

void main() => runApp(
      MaterialApp(
        title: 'RootView',
        showPerformanceOverlay: true,
        checkerboardRasterCacheImages: true,
        home: PageView.builder(
          itemBuilder: (BuildContext _, int index) {
            return CustomPaint(
              isComplex: true,
              willChange: false,
              child: CostlyToRasterize(),
            );
          },
        ),
      ),
    );