Performant blur/opacity in Flutter?

Question

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 1

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.

Solution 2

I have a similar problem and it also boils down to using canvas and paint. The only problem now is, if I apply a MaskFilter to the image, not much happens despite the enormously high sigma... Only the edge is a little blurred.

Now the question is why is that so? How did you solved this issue?

canvas.drawImageRect(
  image, 
  Offset(0, 0) & srcSize, 
  Offset(-delta, 0) & dstSize, 
  Paint()..maskFilter = MaskFilter.blur(
    BlurStyle.normal, 100.0
  )
); 

For those of you who are interested, I have loaded the image in the init function as follows:

rootBundle.load("assets/gift_1.png").then((bd) {
  Uint8List lst = new Uint8List.view(bd.buffer);
  Ui.instantiateImageCodec(lst).then((codec) {
    codec.getNextFrame().then((frameInfo) {
      image = frameInfo.image;
    });
  });
});

P.s. Unfortunately, I can't write any comments yet; therefore here as a contribution, including solution proposal

Comments

[Mary]

My sigma was only 3. When I was playing around with MaskFilter it seemed like I needed to give it more space than the object I'm blurring, and the object needs to be centered. E.g. if your image is 100 x 100, try making your canvas size 200 x 200 and starting your image at (50, 50). This will give the outline of the blur some space. Maybe also try without any offsets, or try just drawing and blurring a solid colored rectangle first.

[bshears]

Hi Mary, I stuck with this. I'm not sure how should I apply blur using Paint/Canvas. I'd appreciate some tips.

[Mary]

What are you stuck with? May be worthwhile to post a separate question with a code snippet.

[bshears]

I tried using CustomPaint with a few simple examples. But still I have no idea how to apply blur effect to what it's displayed on the screen with use of Paint/Canvas.

[Mary]

Does maskFilter.blur() change anything?