scrolling causes issues (code renderer CPU spike) when using a screenreader (like vimac)

[dennis-damico]

• VSCode Version: 1.51.1
• OS Version: macOS Catalina 10.15.7

Steps to Reproduce:

1. Open VSCode
2. Enable vimac
3. Trigger vimac in vscode (not necessary but will guarantee the issue be reproduced)
4. Open a file in vscode an scroll / move cursor around. You will see the window lag and CPU spike

Does this issue occur when all extensions are disabled?: Yes

Note: I'm not entirely sure that vimac is a screenreader though i believe it is because when i first enabled it vscode displayed a message (only time ive ever seen this) mentioning Controls whether the editor should run in a mode where it is optimized for screen readers (setting this to on does not help btw)

[dennis-damico]

If anyone looks further into this may be worth looking here as well in case it's somehow related to vimac implementation (though im not sure how vimac would cause high cpu on the code renderer process)

[isidorn]

Thanks for the feedback. Do you see the same when you use vimac and chrome, for example this page https://bocupp-microsoft.github.io/sample-code/textarea/setselectionrange-performance.html

If you see slowness then could you please file an issue against Chrome?
If not, do you see slowness with other Electron apps and vimac?

[dennis-damico]

I went to the link you sent and did not experience any issues there. Slack and Bitwarden (though bitwarden is pretty minimal so maybe a bad comparison) both run fine as well (cannot tell a difference when vimac is enabled vs disabled)

[dexterleng]

Note: I'm not entirely sure that vimac is a screenreader

Yes, It uses AXManualAccessibility to be able to read the element tree.

[dexterleng]

This is likely a chromium accessibility performance issue, not a VSCode or electron one.

See the original discussion on adding AXManualAccessibility:
electron/electron#7206

[isidorn]

@dexterleng yes sounds like Chromium. Best would be if we could get reproducable steps for Chrome, so we can file an issue in the Chromium repository.