fwiw, Xorg already had this, since you can set the DPI for each display through RandR/xrandr. In both X11 and Wayland it's up to the toolkit to actually detect the setting and rasterise accordingly.
Wayland actually went backwards in this respect by using "integer scales" (eg, 1, 2, 3) instead of fine-grained DPIs (eg, 96, 192, 288), so using a scale of 1.5 would result in downscale blur (toolkit sees scale as 2, then the compositor scales it down to 75%), whereas in Xorg you could just set the DPI to 144, and the toolkit could theoretically render at the correct resolution. As far as I know Qt was the only toolkit to actually do this automatically, but that's not X11's fault.
Wayland has at least since fixed this in the form of "fractional scaling" [1], but here's [0] an old thread on HN where I complained about it and provided screenshots of the resulting blur.
[1] Doing some quick searching it seems like this is still unsupported in Gtk3/Gtk4, maybe planned for Gtk5? Apparently Firefox has only just added support (December 2025), 3 years after the fractional scaling protocol was released. Seems ridiculous to me that Wayland failed to get this right from the start.
These days Xinerama is the only mainstream tool for dual head, but there used to be others. Nvidia Twinview was one. I bought my first dual head box in 1996 with two Matrox Millennium cards (although it mainly ran NT4) and those cards later went into my dual Athlon XP machine. That ran SUSE until Ubuntu came out.
Xinerama isn't a sine qua non. It's just easy so it became ubiquitous. Maybe it's time to replace it.
It's the same on Wayland. The client (usually part of a toolkit like Gtk/Qt) needs to subscribe to notifications [0] from the server so it can decide the raster size of the surface it wants to draw to. Qt does this on X11 by detecting when your window moves to a screen with another DPI and resizing/rescaling.
I guess the "third" program would be something like xrandr, so the Wayland analogue to that would be wlr-randr (for wlroots compositors), or some other DE-specific tool for configuring screen sizes. Again there's no fundamental difference here.
fwiw, Xorg already had this, since you can set the DPI for each display through RandR/xrandr. In both X11 and Wayland it's up to the toolkit to actually detect the setting and rasterise accordingly.
Wayland actually went backwards in this respect by using "integer scales" (eg, 1, 2, 3) instead of fine-grained DPIs (eg, 96, 192, 288), so using a scale of 1.5 would result in downscale blur (toolkit sees scale as 2, then the compositor scales it down to 75%), whereas in Xorg you could just set the DPI to 144, and the toolkit could theoretically render at the correct resolution. As far as I know Qt was the only toolkit to actually do this automatically, but that's not X11's fault.
Wayland has at least since fixed this in the form of "fractional scaling" [1], but here's [0] an old thread on HN where I complained about it and provided screenshots of the resulting blur.
[0] https://news.ycombinator.com/item?id=32021261
[1] Doing some quick searching it seems like this is still unsupported in Gtk3/Gtk4, maybe planned for Gtk5? Apparently Firefox has only just added support (December 2025), 3 years after the fractional scaling protocol was released. Seems ridiculous to me that Wayland failed to get this right from the start.