The method used is not guaranteed to work on all Wayland compositors,
so offer a way out. We need to support it anyways in case xdg_output
or wp_viewporter protocols are not available.
Currently, we scale the desktop up to the next largest integer, and rely on
the wayland compositor to scale it back down to the correct size.
This is obviously undesirable.
In this commit, we attempt to detect the actual fractional scaling by finding
the current active mode in wl_output, and dividing it by the logical screen
size reported by xdg_output, taking into consideration screen rotation.
We then use wp_viewporter to set the exact buffer and viewport sizes if
fractional scaling is needed.
We don't necessarily need `wl_output.release`, which is the only
addition in v3.
This allows Looking Glass to run on Ubuntu 20.04 without having to go
difficult lengths to acquire newer Wayland packages. Since 20.04 is an
LTS release, this seems worthwhile for the small amount of complexity
this introduces.
Fixes
https://forum.level1techs.com/t/latest-build-allow-inhibiting-shortcuts-dialog-ubuntu/168684/6.
If the scale factor of an wl_output changes while the client is running,
the maximum scale factor is not updated. This may result in incorrect
scaling.
Therefore, when the scale factor is changed, we should generate a
resize event.
