Flutter給控件實現鉆石般的微光特效

Shimmer(
  baseColor: const Color(0x08ffffff), // 背景顏色
  highlightColor: Colors.white, // 高光的顏色
  loop: 2, // 閃爍循環次數，不傳默認一直循環
  child: Image.asset('assets/images/watermelon.png',width: 325, height: 260, fit: BoxFit.contain),
)

@override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        // 底層控件
        widget.child,
        // 覆蓋閃爍微光
        AnimatedBuilder(
          animation: _controller,
          child: widget.child,
          builder: (BuildContext context, Widget? child) => _Shimmer(
            child: child,
            percent: _controller.value,
            direction: widget.direction,
            gradient: widget.gradient,
          ),
        )
      ],
    );

  late AnimationController _controller;
  int _count = 0;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(vsync: this, duration: widget.duration)
      ..addStatusListener((AnimationStatus status) {
        if (status != AnimationStatus.completed) {
          return;
        }
        _count++;
        if (widget.loop != 0 && _count < widget.loop) {
          _controller.forward(from: 0.0);
        }
      });

    if (widget.loop == 0) {
      _controller.repeat();
    } else {
      _controller.forward();
    }
  }

class _ShimmerFilter extends RenderProxyBox {
  ShimmerDirection _direction;
  Gradient _gradient;
  double _percent;

  _ShimmerFilter(this._percent, this._direction, this._gradient);

  @override
  ShaderMaskLayer? get layer => super.layer as ShaderMaskLayer?;

  set percent(double newValue) {
    if (newValue != _percent) {
      _percent = newValue;
      markNeedsPaint();
    }
  }

  set gradient(Gradient newValue) {
    if (newValue != _gradient) {
      _gradient = newValue;
      markNeedsPaint();
    }
  }

  set direction(ShimmerDirection newDirection) {
    if (newDirection != _direction) {
      _direction = newDirection;
      markNeedsLayout();
    }
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      final double width = child!.size.width;
      final double height = child!.size.height;
      Rect rect;
      double dx, dy;
      if (_direction == ShimmerDirection.rtl) {
        dx = _offset(width, -width, _percent);
        dy = 0.0;
        rect = Rect.fromLTWH(dx - width, dy, 3 * width, height);
      } else if (_direction == ShimmerDirection.ttb) {
        dx = 0.0;
        dy = _offset(-height, height, _percent);
        rect = Rect.fromLTWH(dx, dy - height, width, 3 * height);
      } else if (_direction == ShimmerDirection.btt) {
        dx = 0.0;
        dy = _offset(height, -height, _percent);
        rect = Rect.fromLTWH(dx, dy - height, width, 3 * height);
      } else {
        dx = _offset(-width, width, _percent);
        dy = 0.0;
        rect = Rect.fromLTWH(dx - width, dy, 3 * width, height);
      }
      layer ??= ShaderMaskLayer();
      layer!
        ..shader = _gradient.createShader(rect)
        ..maskRect = offset & size
        ..blendMode = BlendMode.srcIn;
      context.pushLayer(layer!, super.paint, offset);
    } else {
      layer = null;
    }
  }

  double _offset(double start, double end, double percent) {
    return start + (end - start) * percent;
  }
}

class _Shimmer extends SingleChildRenderObjectWidget {
  @override
  _ShimmerFilter createRenderObject(BuildContext context) {
    return _ShimmerFilter(percent, direction, gradient);
  }
  @override
  void updateRenderObject(BuildContext context, _ShimmerFilter shimmer) {
    shimmer.percent = percent;
    shimmer.gradient = gradient;
    shimmer.direction = direction;
  }
}