Webengine backend with smooth scrolling enabled is jittery while scrolling

[pkillnine]

I posted this issue on the Qt bug tracker.

qutebrowser v0.9.0
Git commit: v0.8.0-2066-g282180e76 (2017-01-08 00:21:57 +0000)
Backend: Webengine

To replicate:

• Open Qutebrowser with --backend webengine

• Enable smooth scrolling (:set ui smooth-scrolling true)

• Scrolling this example webpage will be very jittery and not smooth at all.

• However, if that webpage is within a html frame, then scrolling the page is very smooth.

[pkillnine]

Hmm, I find on qute://help/settings.html that the jittering stops if I :set tabs show never. Other websites, like store.steampowered.com are also smoother when scrolling, but still jittery.

The example webpage is still jittery when scrolling however.

Update: Hiding the statusbar too completely eliminates all scroll-jittering on all webpages for me.

[The-Compiler]

You mentioned seeing the same in QupZilla, so closing this as a QtWebEngine issue.

[wezzynl]

I know that this issue is closed but I just noticed that when I do :set tabs show never and directly after that :set tabs show always the jitteryness is gone and stays gone. The jitteryness is very apparent as I have a very high key repeat rate. After the "trick", all is well. P.s. running latest git version and on MacOS Sierra 10.12.3.

[wezzynl]

Actually. That tab show never/always was just a coincidence. I can reliably get the scrolling to be non-jerky responsive by doing this:

1. Go to a website that has loads of content so you can scroll
2. Use j/k to move down/up
3. Observe it being really jerky and laggy
4. Hit gg to jump to the top of the page
5. Use j/k to move down/up
6. Observe smooth, non-laggy and responsive scrolling

[The-Compiler]

@wezzynl Can you please also check how things look in QupZilla for you? They also have a .dmg for OS X available.

[wezzynl]

Sure. Just tried, QupZilla seems to work fine when using the arrow keys. Though I have to also mention that Qutebrowser also works fine when I use the arrow keys, it is only laggy and jerky when using j/k.

Also: After gg the lagging stays gone for new tabs etc. It only returns when I exit and restart Qutebrowser.

[The-Compiler]

That's weird... All hjkl does is faking arrow keys.

[dset0x]

I can observe this too. No difference between arrow keys / j/k / mouse scrolling from what I can tell.

Intel HD Graphics 4600
xf86-video-intel c28e62f94f15c9f5c4fb0744588f08ae18e4a9b5 [with dri,sna,uxa]
X Server 1.18.4 [with glamor]

Ping @pkill-nine

Edit: I wouldn't call the framed version butter smooth, but definitely smoother.

[pkillnine]

Interesting, for me a page spawned from right-clicking a page and clicking "View Page Source" is completely smooth. If I run :view-source it's not smooth.

[The-Compiler]

@pkill-nine Those are two different source views (Chromium's vs. qutebrowser's one generated with pygments)

[The-Compiler]

As tests here seem to be inconclusive and this happens outside of qutebrowser as well, I'm closing this.

[braham-snyder]

With either tabs or the status bar visible (or both), I'm getting jumpy scrolling despite smooth-scrolling on Mac OS X (El Capitan) and Windows (10) using qutebrowser v0.11.0.

On both platforms, with both the tabs and status bar invisible, scrolling is buttery-smooth. On OS X, QupZilla scrolls smoothly for me (though it has that slow-scrolling Qt bug fixed in 5.9; didn't test QupZilla on Windows, but I could if it helps anyone).

[The-Compiler]

#2822 might help - if not, I doubt there's anything qutebrowser can do.

[The-Compiler]

Turns out this happens due to QtWebEngine emitting a scrollPositionChanged multiple times per scroll with smooth scrolling, which causes all UI things potentially having a scroll position to be redrawn, taking a handful of milliseconds (multiple times).

This should probably help already, but I'd like someone with those problems to test it:

diff --git a/qutebrowser/browser/webengine/webenginetab.py b/qutebrowser/browser/webengine/webenginetab.py
index 4de4bf26f..09df38e82 100644
--- a/qutebrowser/browser/webengine/webenginetab.py
+++ b/qutebrowser/browser/webengine/webenginetab.py
@@ -333,9 +333,10 @@ class WebEngineScroller(browsertab.AbstractScroller):
                 perc_y = min(100, round(100 / dy * jsret['px']['y']))
 
             self._at_bottom = math.ceil(jsret['px']['y']) >= dy
-            self._pos_perc = perc_x, perc_y
 
-            self.perc_changed.emit(*self._pos_perc)
+            if self._pos_perc != (perc_x, perc_y):
+                self._pos_perc = perc_x, perc_y
+                self.perc_changed.emit(*self._pos_perc)
 
         js_code = javascript.assemble('scroll', 'pos')
         self._tab.run_js_async(js_code, update_pos_cb)

Maybe some more optimizations are needed though.

[The-Compiler]

I pushed that now - I'd still be glad if someone could check the difference between tabs.show being always/never with that.

[The-Compiler]

I've had to revert this as it breaks various tests relying on it. I'll need to take a closer look first.

[braham-snyder]

FWIW, with that patch I am indeed seeing significantly smoother smooth scrolling when the tabs and/or the status bar are visible. It's not quite as smooth as it is without the UI bars visible, but it's definitely better than before.

[The-Compiler]

I've now pushed various improvements (hopefully) for this to the latest master. Can someone check how things are now?

[ghost]

I'm using qutebrowser-git from the AUR and it appears to be much better, but still not as great as something like VimFX or Vimium. Here's a 60fps video of qutebrowser on the left, and Firefox 57+Vimium on the right (though in hindsight I think it would have been more meaningful to use chromium instead). I should note that these are all scrolled with j/k, not the mouse. The mouse exhibits similar symptoms

scroll.mp4.zip

[braham-snyder]

On OS X El Capitan I see similar results on that same bootstrap site. On sites like Wikipedia, however (video attached, with comparisons to Firefox and Chrome), qutebrowser seems to scroll more smoothly (well, at least usually -- e.g., the final scroll in my attached video is a bit choppy).

qb_scroll_wikipedia.mov.zip

[The-Compiler]

https://codereview.qt-project.org/#/c/209352/ might also help here - I don't think there's much more qutebrowser can do, so I'm closing this.