Fenix: [Bug] Scrolling sometimes reacts late on touch input

[Wasseranomalie]

Steps to reproduce

• Open https://github.com/mozilla-mobile/fenix/issues
• Switch to desktop version
• Scroll up and down the page at intervals of a few seconds

Expected behavior

Scrolling happens immediately

Actual behavior

Page scrolls with noticeable delay

https://www.youtube.com/watch?v=Pf5xt_fGQHE

Device information

• Android device: Nexus 5X, Android 8.1
• Fenix version: 1.0.1925 (Build #11691815)

[sblatz]

@Wasseranomalie are you still able to reproduce this?

[Wasseranomalie]

@sblatz yes, it is still happening on Nightly 190719 (Build #12001827)

[kbrosnan]

Scrolling in content makes it a likely GeckoView bug. @cpeterso do we have anything like this currently?

[kbrosnan]

@Wasseranomalie if you have some more time to investigate this are you able to reproduce the scrolling problems on Reference Browser?

[Wasseranomalie]

Yes, it is also happening there.

Reference Browser 1.0.1929 (Build #12021213)

On old Firefox (nightly) there is no input lag, so it seems to be a new issue when using geckoview.

[cpeterso]

Thanks for reporting this bug, @Wasseranomalie. This does sound like a GeckoView problem, so I filed a GeckoView bug report: https://bugzilla.mozilla.org/show_bug.cgi?id=1567977

[cpeterso]

@Wasseranomalie - Can you still reproduce this scrolling in Fenix and Reference Browser? Can you reproduce the problem on any other devices or web pages?

I'm not able to reproduce an obvious scrolling problem on my Moto G5 running Android 8.1. Are there any extra steps to reproduce? Did you zoom the page before scrolling? The GitHub desktop page's fonts are tiny on my phone because the page width fits the screen width unless I use an expand-to-zoom gesture. Does that make a difference for you?

[Wasseranomalie]

Yes, I can still reproduce it. Unfortunately I don't have another device available for further testing.

The only step to take is to request the desktop version of the website. It seems to become more frequent when zooming out completely to see the whole page width.

Another site I found was the desktop-version of YouTube (and if not done automatically zoomed out completely). There this scrolling problem appears on every try on my device, so maybe you have more luck there to reproduce this issue.

Tested on:
Firefox Preview: Nightly 190827 06:04 (Build #12390613)
Reference Browser: 1.0.1935 (Build #12391232)

[cpeterso]

Thanks. I'll add your comments to the GeckoView bug report.

Can you also reproduce the scrolling issue in Firefox for Android? The current version is 68.

[Wasseranomalie]

On Firefox for Android 68 this issue only happens very rarely and when it happens the delay is very short. Scrolling is far worse on Firefox Preview with a delay of up to one second after touching the display (vs. maybe <0.2 seconds on Firefox for Android 68).
I've made another video showing this issue: https://youtu.be/UcqER9irdOo (the delay does not become shorter after all thumbnails have been loaded)
You can also see at the end of the video that after scrolling has started, there is no delay when changing direction anymore so there is just a huge delay when you want to start scrolling.

[cpeterso]

I've made another video showing this issue: https://youtu.be/UcqER9irdOo (the delay does not become shorter after all thumbnails have been loaded)

Thanks for the screen capture. It clearly shows the slow response when you start scrolling.

[PranavBhattarai]

Mine is worse.
This doesn't happen all the time.
But I have noticed the browser lag while scrolling the web page. It happens like 1 out of 5 times.

I have also recorded screencast video as proof when I was using m.facebook.com to see more stupid posts, I scrolled.

Firefox version: 4.3.0 (latest to the time of the comment).
Device: Oneplus 5
OS: Oxygen OS Android 9

Hope this helps.