Shimmer loading product grid

import 'package:flutter/material.dart';

/// Sweeps a highlight across every skeleton box placed under it.
class Shimmer extends StatefulWidget {
  const Shimmer({super.key, required this.child});
  final Widget child;

  @override
  State<Shimmer> createState() => _ShimmerState();
}

class _ShimmerState extends State<Shimmer> with SingleTickerProviderStateMixin {
  late final AnimationController _c =
      AnimationController(vsync: this, duration: const Duration(milliseconds: 1400))
        ..repeat();

  @override
  void dispose() {
    _c.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final base = Theme.of(context).colorScheme.surfaceContainerHighest;
    final glow = Theme.of(context).colorScheme.surface;
    return AnimatedBuilder(
      animation: _c,
      child: widget.child,
      builder: (context, child) => ShaderMask(
        blendMode: BlendMode.srcATop,
        shaderCallback: (rect) => LinearGradient(
          colors: [base, glow, base],
          stops: const [0.25, 0.5, 0.75],
          // Slide the gradient from fully left to fully right of the box.
          transform: _Slide(_c.value),
        ).createShader(rect),
        child: child,
      ),
    );
  }
}

class _Slide extends GradientTransform {
  const _Slide(this.t);
  final double t;
  @override
  Matrix4? transform(Rect bounds, {TextDirection? textDirection}) =>
      Matrix4.translationValues(bounds.width * (t * 3 - 1.5), 0, 0);
}

class ShimmerProductGrid extends StatelessWidget {
  const ShimmerProductGrid({super.key, this.count = 6});
  final int count;

  @override
  Widget build(BuildContext context) {
    return Shimmer(
      child: GridView.builder(
        physics: const NeverScrollableScrollPhysics(),
        padding: const EdgeInsets.all(16),
        gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 2, mainAxisSpacing: 12, crossAxisSpacing: 12, childAspectRatio: 0.72,
        ),
        itemCount: count,
        itemBuilder: (_, _) => Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Expanded(child: _box(double.infinity, radius: 16)),
            const SizedBox(height: 8),
            _box(110, h: 12),
            const SizedBox(height: 6),
            _box(60, h: 12),
          ],
        ),
      ),
    );
  }

  Widget _box(double w, {double h = 0, double radius = 6}) => Container(
        width: w,
        height: h == 0 ? null : h,
        decoration: BoxDecoration(color: Colors.white, borderRadius: BorderRadius.circular(radius)),
      );
}