Generally, Scrollbar scrolling happens in the main thread in the Chrome browser, Microsoft which is contributing to Chromium has found scrolling the vertical scrollbar by dragging isn’t great when the main thread is busy. Microsoft has addressed this issue with Compositor Threaded Scrollbar scrolling feature in Chromium, as of now, the feature is enabled by default in Canary and Dev versions of Chrome and Microsoft Edge browsers. You can test, feel and see how responsive scrollbar scrolling in Edge or Chrome is by visiting the demo site created by Microsoft.
1. Visit about: flags page latest Chrome Dev/Canary or Microsoft Edge 82 Dev /Canary
2. Set the “Compositor Threaded Scrollbar Scrolling” flag to “Disabled” and restart the browser.
3. Visit this demo site
4. Click on Start animation and further click on “Induce main thread jank”,
5. Now try to drag the scrollbar down, you’ll find it hard.
6. Now change the above-mentioned flag to Default or Enabled and relaunch the browser.
7. If you now follow the 4th step, you’ll notice huge improvements in scrollbar scrolling despite the main thread being janky.
We’ve rolled out new scrolling improvements in Canary and Dev that make scrolling via scrollbar more responsive when the main thread is busy (for example, during long-running JavaScript).
Try it out and let us know what you think! More scrolling improvements coming soon. pic.twitter.com/akHxRlKOCh
— Microsoft Edge Dev (@MSEdgeDev) March 19, 2020
Do note Microsoft is still working on to bring more scrolling improvements to Chromium, for instance, we’ve covered about percent-based scrolling, here, the improvements are specifically landed for a scrollbar in Chrome and Edge browsers.
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