3

In some of the recent activity around the handling of multiple monitors, it seems that some people tend to ignore the "dual-monitor" setup (that is two or more monitors of equal size or having compatible dimensions arranged in close proximity to form one grand display/container) or brush it away as being less common than the "external/secondary-monitor" setup (one primary monitor + zero or more detachable secondary monitors). In my observations they both seem to be comparably common, with dual-monitor setups more common among the desktop/workstation setups (especially in software development offices like mine?) and external/secondary-monitor setups being the norm when using a laptop or attaching temporary external displays for presentations.

In my view, these really are two separate concerns that quite often have conflicting expectations:
In a Dual-monitor setup, you don't expect to detach one of the monitors, and each monitor is equally a primary monitor (though you might want to specify one as the default for newly-opened windows, it seems more common to expect windows to open on the monitor that has the mouse). You also expect such options as to be able to have wallpapers, panels, and even windows span monitors. Activities and Virtual Desktops are expected to be shared by all monitors - switching activities or virtual desktops switches all monitors together (though it could be nice to be able to switch virtual desktops separately, but that is a different issue) because it is expected to be one singular grand display.
On the other hand in an external/secondary-monitor setup, you expect that one monitor is the primary monitor and that other monitors are secondary and transient (connected for some duration and then disconnected when you are finished using it). You don't want wallpapers, panels, or windows to span monitors, and prefer a more explicit mechanism of moving things between monitors. You would also want to have separate (temporary) activities and virtual desktops for each monitor, and that each monitor is treated as a separate display.

What if these separate concerns were determined via config setting (in the display settings)?
Selecting the dual-monitor option would ensure that there are no gaps between monitors, that the monitors have compatible dimensions, and that the monitors are not offset. It would then enable a set of dual-monitor-only config options like spanning wallpapers, spanning panels, all-monitor maximization of windows (a non-default option in addition to the still-default single-monitor maximization), etc. Activities and virtual desktops are unified accross monitors.
If you select that your multi-monitor setup is an external/secondary-monitor setup then you wouldn't get the spanning options, but you could get per-display activities and/or virtual desktops.

There could also be the possibility of having both, if e.g. you have two primary monitors arranged in a dual-monitor setup, then attach an external display for a presentation. In this case, the dual-monitor options would only apply to the two primary monitors, and you would get the separate activities/virtual desktops for the external display.

Yes. Multiscreem is always a problem for me in KDE.

I hope that I can have a scheme list to choose when I plug in/ plug out the monitor.