Microsoft wants to improve scrolling performance in Chromium

Laurent Giret

Microsoft is currently hard at work on a new version of its Edge browser based on the Chromium open source project, and last year the company announced plans to become a “significant contributor to the Chromium project.” Microsoft’s contributions could benefit all Chromium-based browsers, but one area where Microsoft would like to make an impact is mouse scrolling performance.

In a recent proposal spotted by, Microsoft explained that the way EdgeHTML handles mouse scrolling is better than the “janky” performance that Chromium sometimes provides:

Scrollbar scrolling using the mouse happens on the main thread in Chromium. If the main thread is busy (due to reasons like long running JS, etc), scrolling by clicking on the scrollbar will appear to be janky as the events keep getting queued up on the MainThreadEventQueue, waiting for the main thread to free up. We observe on average scrollbar drags have ~2-4x higher latency in Chromium as compared to EdgeHTML today, worse on particularly busy sites.  We attribute this gap primarily to EdgeHTML’s feature for off-thread scrollbar drags.  By avoiding the main thread in Chromium as well, we believe we can bring the performance of scrollbar drags more in line with what we observe in EdgeHTML.

The Chromium logs also show that Microsoft recently filed an issue with an attached HTML file to prove its point. A Chromium developer has since answered that the team was looking into it, to which Microsoft answered that it has already started prototyping and will “send out an intent-to-implement shortly.”

These discussions all happened last week, and it may take some time before the Chromium team eventually accepts this feature request from Microsoft. But if this does happen, all Chromium-based browsers on all platforms could soon provide the same smooth scrolling performance that Microsoft Edge users currently enjoy on Windows 10 PCs.