Bad side-by-side scrolling performance with syntax highlighting enabled

The scrolling performance in a side-by-side window becomes really bad sometimes when highlighting is enabled. It’s not uncommon for the CPU to hit over 100%, which causes the scrolling to freeze. It doesn’t really seem related to the file size, it also happens for files of about 200 to 300 lines.

If I understand the Google Chrome profiler correctly, then most of the time is spend on the line Prism.highlightElement(preElement);. This seems to be triggered by the scrolling event.

I haven’t looked into it any further, as I don’t really understand why the highlighter should run each time someone scrolls. But it would be great if this could be improved somehow.

[Daanvm]

Update after 1 week: I’ve not noticed any glitches or performance issues anymore. Thank you so much for this great update! 🎉

[nickpeirson]

Hey @reyronald, thanks for the update.

I’ve done few quick tests and it’s looking better so far. With it enabled, looking at pretty much any side by side diff with syntax highlighting enabled would lock up Chrome, however I’ve tried a few diffs with the latest extension version and it’s remained mostly responsive. May be a couple of small stalls still, but nothing like the previous lockups I was seeing.

I’ll keep an eye on it throughout the week and see if I hit any diffs that still cause problems, but so far so good! Thanks very much!