Possible to determine bar's "output" (current monitor) from a cffi module?

[justbuchanan]

First party modules have access to a Bar instance, which contains the name of the output the bar is being displayed on. For example, here it's used in the niri module:

Waybar/src/modules/niri/workspaces.cpp

Line 41 in 161367d

return ws["output"].asString() == bar_.output->name;

Is it possible to access the output name from a cffi module?

[LordMZTE]

I've run into this problem, too. My attempted solution was to use gdk_screen_get_monitor_plug_name (code), but unfortunately, this seems to report the wrong output name when using multiple outputs.

[B2krobbery]

Maybe Waybar could pass the output name to cffi modules as an environment variable?
For example:WAYBAR_OUTPUT=eDP-1
Then scripts (Python, etc.) can read it easily without relying on GDK, which seems unreliable with multiple monitors.
This might be a simple way to solve it. Would this be acceptable?

[LordMZTE]

Environment variables likely couldn't work here, because they're per-process, so there's no way to have them be different per bar. Instead, I think a good API would be to pass an opaque pointer to the Bar object in wbcffi_init_info and provide an API with a function such as wbcffi_bar_get_output_name that returns the output name.

[LordMZTE]

I've found a workaround: The GtkWindow objects for the bars are assigned the name of their output as a CSS class by Waybar. This doesn't technically allow us to get the output name since we don't know which of the CSS classis is the output name, but it does allow us to check if a given string is the name of the current output, which was enough for my use case.

Code