flutter_app_watermark 1.0.1

Watermark your entire Flutter app in one line, or scope it to a single widget. Text, angle, opacity and spacing are configurable. Pure Dart, no dependencies.

flutter_app_watermark

Watermark your entire Flutter app in one line.
Dialogs, bottom sheets and pushed routes included — nothing covers it.

▶ Try it live  ·  简体中文

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Why

Screenshots of internal dashboards, contracts and customer data leak all the time. A watermark carrying who was looking and when turns an anonymous screenshot into a traceable one — and makes people think twice before taking it.

Doing that properly is trickier than it looks: the watermark has to survive route changes, sit above modals, never swallow a tap, never get read aloud by a screen reader, and not cost you frames. This package does all of it in one widget.

One line, whole app	Wrap WatermarkScope outside MaterialApp — every route, dialog, bottom sheet and page transition is covered
Or just one widget	Watermark scopes it to a single card without touching its layout
Live updates	Change the text after sign-in; only the watermark layer repaints, your widget tree doesn't rebuild
Crop-resistant	Staggered rows plus a per-user offset, so a cropped screenshot still points back to one person
Invisible to input	IgnorePointer plus a hitTest override — buttons underneath stay tappable
Cheap	Covers only the bounding box the rotation needs, lays out the text once, caches the layer
Zero dependencies	Pure Dart. No native code, no plugins, works on mobile, web and desktop

A watermark deters screenshots and makes leaks traceable — it does not block screen capture. If you need FLAG_SECURE-style blocking, pair this with a dedicated plugin.

Install

dependencies:
  flutter_app_watermark: ^1.0.1

Requires Flutter >=3.27.0.

Quick start

import 'package:flutter_app_watermark/flutter_app_watermark.dart';

final watermark = WatermarkController();

void main() {
  runApp(
    WatermarkScope(              // ← outside MaterialApp
      controller: watermark,
      child: const MyApp(),
    ),
  );
}

// after sign-in
watermark.update(lines: [
  '${user.name} ${user.maskedPhone}',
  DateFormat('yyyy-MM-dd HH:mm').format(DateTime.now()),
]);

That's the whole integration. Everything below is optional.

Scope it to one widget

Watermark(
  lines: const ['Jane Doe · #10086', 'Internal use only'],
  style: const WatermarkStyle(opacity: 0.22, rotation: -25),
  child: const ContractCard(),
)

Watermark sizes itself to its child and never stretches it. Watermark.text('...') is the single-line shorthand, and enabled: false hides it without changing the tree.

Read the controller from anywhere

WatermarkScope.of(context).update(lines: ['Jane Doe · [phone]']);
WatermarkScope.of(context).update(enabled: false);   // e.g. internal accounts

Styling

const WatermarkStyle(
  opacity: 0.15,
  rotation: -30,
  fontSize: 14,
  columnSpacing: 80,
  rowSpacing: 60,
  staggered: true,
)

All WatermarkStyle fields

Field	Type	Default	Description
opacity	double	0.15	Opacity 0–1, multiplied with the alpha already in color
rotation	double	-30	Degrees, negative is counter-clockwise, around the canvas center
color	Color	0xFF9E9E9E	Text color
fontSize	double	14	Font size
fontWeight	FontWeight	normal	Font weight
fontFamily	String?	null	Font family
lineHeight	double	1.35	Line-height multiplier for multi-line text
textAlign	TextAlign	center	Alignment of the lines inside one tile
rowSpacing	double	60	Vertical gap between rows
columnSpacing	double	80	Horizontal gap between columns
staggered	bool	true	Shift odd rows by half a tile (crop resistance)
offset	Offset	zero	Offsets the whole pattern — useful to shift it per user
maxTiles	int	800	Tile budget per paint; exceeding it thins the grid and warns in debug

WatermarkStyle is an immutable value object — use copyWith for partial changes.

Making leaks traceable

Put three things in the watermark: who, a unique key, and when.

watermark.update(lines: [
  '${user.name} ${user.maskedPhone}',
  'ID ${user.employeeId}',
  DateFormat('yyyy-MM-dd HH:mm').format(DateTime.now()),
]);

Then shift the pattern per user. Even if most of a screenshot is cropped away, where the remaining tiles sit still identifies one account:

final seed = user.id.hashCode;
style.copyWith(offset: Offset((seed % 37).toDouble(), (seed % 23).toDouble()));

What it covers

WatermarkScope lives at the very top of the widget tree.

Covered — every route including during transitions · showDialog / showModalBottomSheet / SnackBar · the status bar area and safe areas · Flutter layers above platform views such as WebView and maps.

Not covered — system permission dialogs and the IME panel · the system's post-screenshot preview screen · anything after the user leaves the app. All of it lives outside Flutter, so no pure-Dart package can reach it.

Performance

• Fills only the bounding box the rotation actually needs (w·|cosθ| + h·|sinθ| × w·|sinθ| + h·|cosθ|) instead of naively covering twice the diagonal — the naive approach draws roughly 4–5× more tiles
• Text is laid out once per painter and reused; scrolling and rotation don't re-run layout
• The layer sits behind a RepaintBoundary and is marked isComplex + !willChange, so app repaints don't drag it along
• maxTiles is a backstop, so one mistyped font size can't tank the frame rate

On a 390×844 phone with default settings that's about 110 tiles in a single cached layer.

Example app

cd example && flutter run

A small sales app that adapts from phone to desktop: drag angle, opacity, font size and spacing live, and check that dialogs, bottom sheets and pushed routes are all covered. Ships with 13 locales, RTL included.

Tests

flutter test

Support

If this package saved you some time, a 👍 on pub.dev or a ⭐ on GitHub helps other people find it.

Hit a bug, or have a case it doesn't cover yet? Open an issue — happy to talk it through. PRs welcome too.

License

MIT