cutout 1.0.2

A mask-driven cutout widget — punch through content to reveal what's beneath. 蒙版镂空组件，将指定形状从内容中挖除，透出底层背景。

🪟 Cutout

A mask-driven cutout widget — punch through content to reveal what's beneath.

蒙版镂空组件，将指定形状从内容中挖除，透出底层背景。

✨ Features / 特性

• Any widget as mask — Use icons, text, images, or any widget as the cutout shape
• Images as mask — Use transparent Image (eg. PNG) as cutout shapes
• Flexible alignment — Full control over mask positioning via alignment

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• 任意组件做蒙版 — 支持图标、文字、图片或任意组合作为镂空形状
• 图片蒙版 — 使用带透明度图片（如 PNG ）作为镂空底图
• 灵活对齐 — 通过 alignment 参数完全控制蒙版位置

🚀 Getting started / 快速开始

Install via pub.dev → pub.dev/packages/cutout/install

📖 Usage / 使用示例

https://runoob-coder.github.io/flutter_cutout_widget/

Basic cutout with an icon / 使用图标镂空

Cutout(
  alignment: Alignment.center,
  maskChild: const Icon(Icons.star, size: 50),
  child: Container(
    width: 100,
    height: 100,
    color: Colors.blue,
  ),
)

🪟 Cutout with text / 使用文字镂空

Cutout(
  alignment: Alignment.center,
  maskChild: const Text(
    'Cutout',
    style: TextStyle(fontSize: 30, fontWeight: FontWeight.bold),
  ),
  child: Container(
    width: 200,
    height: 50,
    color: Colors.orange,
  ),
)

Composable mask (icon + text) / 组合蒙版（图标+文字）

Cutout(
  alignment: Alignment.center,
  maskChild: const Row(
    mainAxisSize: MainAxisSize.min, // must be min / 约束必须为 min
    children: [
      Text('Cutout', style: TextStyle(fontSize: 30, fontWeight: FontWeight.bold)),
      Icon(Icons.auto_awesome, size: 30),
      Text('Widget', style: TextStyle(fontSize: 30, fontWeight: FontWeight.bold)),
    ],
  ),
  child: Container(
    width: 300,
    height: 50,
    color: Colors.green,
  ),
)

🪟 Cutout over images / 图片镂空

SizedBox(
  height: 120,
  child: Stack(
    alignment: Alignment.center,
    children: [
      // Background image showing through the holes / 底层背景透过镂空区域显示
      Image.asset('assets/background.jpg'),
      Cutout(
        alignment: Alignment.center,
        maskChild: const Row(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text('Hello', style: TextStyle(fontSize: 56, fontWeight: FontWeight.w900)),
            FlutterLogo(size: 70),
            Text('World', style: TextStyle(fontSize: 56, fontWeight: FontWeight.w900)),
          ],
        ),
        child: Image.asset(
          'assets/gradient.jpg',
          fit: BoxFit.fill,
          width: double.infinity,
        ),
      ),
    ],
  ),
)

Transparent PNG as mask / 透明度图片做蒙版

Cutout(
  alignment: Alignment.center,
  maskChild: Image.asset('assets/magic.png', height: 220), // use an image with transparency / 请使用透明度图
  child: Image.asset('assets/16-fractal-glass-hero-gradients.jpg'),
)

⚙️ How it works / 原理

1. Content children → rasterized into offscreen buffer
2. Mask child drawn with BlendMode.dstOut → opaque mask pixels punch holes
3. Buffer composited back onto canvas

1. 内容子组件 → 光栅化到离屏缓冲区
2. 蒙版子组件以 BlendMode.dstOut 绘制 → 不透明像素在内容上镂空
3. 缓冲区合成回Canvas

⚠️ Important / 重要提示

Important

Content children that push their own composited layers — such as AnimatedSwitcher, Opacity, FadeTransition, ClipRect, Transform, BackdropFilter, etc. — will have those layers composite outside the internal saveLayer buffer, defeating the mask effect.

Avoid nesting layer-pushing widgets inside Cutout.child !

This is a fundamental limitation of Flutter's compositing pipeline and cannot be fixed at the framework level — it would require changes to the Flutter engine itself. If you have a solution, PRs are welcome!

RenderCutout.paintStack isolates content inside a canvas.saveLayer buffer, but when context.paintChild draws a content child (e.g. FadeTransition inside AnimatedSwitcher), the child may push its own composited layer (e.g. OpacityLayer) into the layer tree via pushOpacity. These layers become siblings of the current ContainerLayer and escape the saveLayer buffer, breaking the dstOut cutout.

---

Important

如果 Cutout.child 中包含会推送自身合成层的组件（如 AnimatedSwitcher、Opacity、FadeTransition、ClipRect、Transform、BackdropFilter 等），这些层会在内部 saveLayer 缓冲区外部合成，导致镂空失效。

避免在 Cutout.child 中嵌套会推送层的组件！

这是 Flutter 合成管线的底层限制，无法在框架层修复 — 需要调整 Flutter 引擎本身。如果你有解决方案，欢迎贡献 PR！

RenderCutout.paintStack 使用 canvas.saveLayer 做外层隔离， 但 context.paintChild 绘制内容子节点时，子节点（如 AnimatedSwitcher 内部的 FadeTransition） 可能通过 pushOpacity 等调用向 layer tree 推入独立的合成层（如 OpacityLayer）。 这些合成层是当前 ContainerLayer 的兄弟节点，会逃逸出 saveLayer 缓冲区，导致dstOut镂空失效。

📋 API

Parameter	Type	Default	Description / 说明
maskChild	Widget	required	The shape to punch through / 用于镂空的形状
child	Widget	required	The content to be cut through / 被镂空的内容
alignment	AlignmentGeometry	Alignment.topStart	Mask alignment / 蒙版对齐方式
textDirection	TextDirection?	null	Text direction for alignment / 文本方向
fit	StackFit	StackFit.loose	How to size the stack / Stack尺寸约束
clip	Clip	Clip.hardEdge	Clip behavior / 裁剪行为

📎 Additional information / 更多信息

• Homepage: GitHub
• Issue Tracker: GitHub Issues

💛 Support / 支持

If Cutout helps you build better UIs, please consider supporting it.
It only takes a few seconds and helps other Flutter developers discover the library.

如果 Cutout 帮助了你，请考虑支持它，只需几秒即可帮助更多 Flutter 开发者发现此库。

• ⭐ Star on GitHub / GitHub 上点星
• 👍 Like on pub.dev / pub.dev 上点赞

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