How can I control a nested sway session with swaymsg independently from a non-nested scroll session?

[maxigaz]

I'd like to test output scaling in sway by running it as a nested session inside scroll, with the intention of seeing how the two compositors behave in this regard.

The command I've been trying to run in the nested session is this:

swaymsg output WL-1 scale 1.2

When I hit enter, scroll crashes.

Similarly, if I try to exit the nested session this way, that ends the outer session:

swaymsg exit

I checked the values of the environmental variables SCROLLSOCK and SWAYSOCK. By default, they have different values. I also made sure WAYLAND_DISPLAY is set correctly in both sessions, in case it might be relevant.

Do I need to do anything else, or is this likely a bug in sway or scroll?

[dawsers]

There could be several things happening here.

The first problem is you cannot really test output quality when running nested. The nested compositor will use the host as a backend, Your WL-1 virtual monitor is just a window rendered by the host compositor. When you resize that window, or even at creation time, its "resolution" changes, it is never what you define for the monitor. If you want to see the real output, you need to run a separate instance of the compositor, either using one dedicated output, or a virtual machine with GPU passthrough.

Other than that, I run sway and scroll nested all the time for debugging purposes, but not for rendering debugging. The main ideas are:

1. I don't have sway installed on my system, I just use a version I build on a work directory. This shouldn't matter, unless you set things up for your sway session using systemd or similar. My system boots as a pure scroll system, and then I run my ~/work/sway/build-debug/sway/sway -c ~/.config/sway/config.debug.
2. My ~/.config/sway/config.debug has to be adapted to be able to run nested, for example, you need to remove most exec things that are already running under scroll, and change your $mod1 to Alt for example, otherwise your key bindings won't work.
3. When you call swaymsg from the nested compositor, you need to call the version you built and is the same version as the nested compositor you are running, any version won't do.

You can definitely run nested sway within scroll, but it is meant for debugging or testing things, not for rendering quality comparisons.

If you are trying to test fractional scaling quality, I made a lot of changes to avoid blur (#88). wlroots/sway has some PR that hasn't merged yet. It does things differently, and when I tested it, it wasn't working for me, so I did my own thing.

[maxigaz]

Thank you for the detailed explanation!

I forgot about the different versions of swaymsg; I was using the one installed systemwise, shipped with v1.11 (just running swaymsg in the terminal) rather than specifying the full path to the build I compiled from source from master.