Enable sharp rendering on Wayland with fractional scaling

[LinqLover]

Right now, when opening the VM in Wayland and having enabled fractional scaling (e.g. 150%), the display is blurry. If I understand correctly, XWayland scales up the original xlib window. I have not yet understood whether there is some way to handle XWAYLAND_SCALE ourselves and tell Wayland/XWayland that we want to scale ourselves, or whether the entire display plugin needs to be migrated to Wayland to enable sharp scaling.

[LinqLover]

Also, primitiveBeCursor does not work correctly in XWayland (including monitors with 100% scaling).

[marceltaeumel]

Also [...]

Please make an extra issue for that. Thank you!

[LinqLover]

More issues with Wayland/XWayland (I don't know which part of the stack):

• Drag'n'drop from host not working properly (the VM emits a dragLeave event when dropping a file on the image; the image responds with the confusing message "Cannot start a second instance of Squeak with the image ...")
• The VM emits five windowDeactivated/windowActivated events on every mouse click, which I only noticed after weeks but at least breaks the mini editors in window titles (shift+click to change label)

Also, primitiveBeCursor does not work correctly in XWayland (including monitors with 100% scaling).

Not reproducible. Sometimes my cursor works fine, sometimes not. I don't yet understand what this depends on (maybe whether I first started my image or first connected my external monitor?).

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Please make an extra issue for that. Thank you!

I'd prefer keeping all observations together in one thread until we understand if and how they are actually (not) related to each other.

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I already tried to research how we could stick with Xlib when supporting XWayland. I tried to nest an alternative X server via Xephyr or Gamescope but couldn't get rid of the blurry upscaling, and this would probably introduce new incompatibilities. Apparently there are options such as force_zero_scaling (system-wide) or scale-monitor-framebuffers (application-specific) available for newer versions of XWayland/Mutter but they seem not to be contained in Ubuntu 24.04.

At this point, I see three possible ways to proceed:

1. Do nothing and wait until support for XWayland gets further improved (I don't know whether it will, and in particular whether these changes will be backported to Ubuntu 24.04)
2. Implement a new display plugin for Linux that natively targets Wayland
3. Build alternative implementations of EventSensor, DisplayScreen>>#beDisplay/class hostWindowTitle: et al., and Cursor>>#beCursor that use FFI instead of a VM plugin. That could be much developer-friendly and also allow us to remove global state from the display logic at the same time (e.g., multiple worlds in multiple VM windows, ...).