Hm, the 4k monitor should ideally not connected as 3840x2160+0+0. Not sure why that's not the case. Can you also attach the output from running 'weston-info' from 'weston' package?

I had a chance to test this so you can ignore my last comment. The resolution is actually what we want. I can reproduce the problem and not sure exactly what is happening. I suspect that we're affected by some buffer size limit when reaching 7680x4320 in resolution. I'll investigate more to see what's the best way to solve that.

For ideal performance on a 4k monitor you probably want to launch VS code using:

$ sommelier -X --scale=0.5 code -w

That also avoids this problem. Notice how the window is now sharp on the external monitor but blurry on the internal panel. The reason we're not doing this by default is because we prioritize the internal display. This problem of have to pick a display that is preferred is hard to avoid for X11 apps. The general solution is for apps to switch to native wayland protocol, and that way be able to handle density changes dynamically.

I've done some more testing and it seems like the issue is specific to electron apps. They seem to start producing rendering artifacts when the resolution is above 4800. I can reproduce the same issue in atom but not in sublime text.

If I disable the internal display (close pixelbook) while vm is running xrandr still says 7680x4320+0+0. But if I start the vm in this state it's 3840x2160+0+0.

Yes. Disabled internal display, is a mode that we fail to support properly in Crostini for X11 apps today. Problem is that without the internal display we don't know what the preferred scale factor should be used for X11 apps. We might need to hard code this for each board or add a new aura shell event.

I'm closing this bug as external display support with internal display also present should now be working properly. I'll open a new bug for the 'disabled internal display' issue.