[SOLVED] Performant blur/opacity in Flutter?

Issue

I love the blurry frost effect using a BackdropFilter (see this).

However, because the BackdropFilter has Opacity and because the widget I’m blurring also has Opacity, the performance is horrendous. This is also because I redraw my widgets a few times a second, but that shouldn’t be an issue given Flutter can go 60fps?

I turned on checkerboardOffscreenLayers and see checkerboards for miles. :O
The checkerboards happen due to blurScreen, not due to widgetToBlur but widgetToBlur does slow down performance probably because (in my real code, not this example) it’s calling setState() multiple times a second.

Is there a more performant way to make blurs/opacities? The link above says to apply opacity to widgets individually. I can’t do that with the blur though (blurScreen below), because the BackdropFilter has to be stacked on top of my widget-that-does-the-redrawing.
I removed the blur effect and my performance is way better (no checkerboards, app doesn’t crash).

build() code in question:

final widgetToBlur = Container(
  child: Opacity(
    opacity: 0.3,
    // In my actual code, this is a Stateful widget.
    child: Text('Spooky blurry semi-transparent text!'),
  ),
);

final blurScreen = BackdropFilter(
  filter: ImageFilter.blur(sigmaX: 3.0, sigmaY: 3.0),
  child: Container(
    decoration: BoxDecoration(
      color: _backgroundColor.withOpacity(0.3),
    ),
  ),
);

return Container(
  child: Stack(
    children: <Widget>[
      widgetToBlur,
      blurScreen,
      Text('This is in front of the blurred background'),
    ],
  ),
);

Solution

I ended up drawing the widgetToBlur once, blurred, with opacity, using Paint and Canvas.

This means it only runs the blur and opacity operations once, in initState(), and never has to be re-rendered-with-blur throughout the lifecycle of the widget.

If anyone else ends up stuck with this, you can leave a comment and I can help out more.

Answered By – Mary

Answer Checked By – Candace Johnson (BugsFixing Volunteer)

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