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Comment by ltrever | Hacker News Reader

Can you pls share smt on how to properly do multi dpi in X? It is hard to find and I struggle with it

The mixed DPI support on X11 is just that each monitor provides a DPI attribute that applications can query. It's up to the application or the toolkit it uses to actually look at this attribute and scale itself properly. In practice, this means that only Qt software will have DPI awareness on multi-monitor setups, and it requires having the "QT_AUTO_SCREEN_SCALE_FACTOR=1" environment variable set for applications that don't explicitly opt into it.

What most X11 users actually do is set the global DPI to that of the highest DPI monitor, and use xrandr to scale down the framebuffer of the lower DPI monitor, which "zooms it out". Note that this has performance and image quality implications. There's a guide on how to do this here: https://blog.summercat.com/configuring-mixed-dpi-monitors-wi...

The irony is that despite the myth to the contrary wayland does not even try to handle mixed DPI at all and only fakes it via the fractional scale hack and X11 has supported mixed DPI from probably day one.

Admittedly X11 mixed DPI was using separate screens which were awkward to deal with and early versions of the unified screen tech (xinarama and xrandr) did not support mixed DPI. And even modern X11 while it provides the needed DPI information requires the application to care enough to support it. Which really means unless the toolkit provides it for free most applications are not going to do anything,

> The irony is that despite the myth to the contrary wayland does not even try to handle mixed DPI at all and only fakes it via the fractional scale hack and X11 has supported mixed DPI from probably day one.

I'm not sure what you're talking about, fractional scaling is just another way to describe DPI. The scale factor is just the DPI divided by 96. If you're referring to windows getting scaled by the compositor for fractional scales, that's only used for older software. Both Qt 6 and GTK 4 support natively rendering window contents at fractional scales on Wayland.

In a fractional scaling setup you first create a homogeneous virtual screen at the dpi wanted then get the right size by scaling the monitors out to fit. A dpi aware application will draw itself at the correct size on the appropriate screen. The main difference is the dpi aware application still looks good on all monitors. where as the fractional scaled stuff suffers scaling artifacts.

Wayland only supports fractional scaling. and there is a good argument that this is a better system, not because it looks better, it does not. but because applications don't have to be aware of it where a mixed dpi requires the application to actively deal with it.

My favored article on the subject is http://wok.oblomov.eu/tecnologia/mixed-dpi-x11/

This + mixed refresh rate are the key selling points of Wayland.

Xorg does per-monitor DPI and per-monitor refresh rate. Debian probably never shipped a version that does, but it works fine on Gentoo Linux.

I've tested per-monitor DPI before, and [0] mentions one way to do it. I tested per-monitor refresh just now. Using the xrandr CLI to set the refresh rate to 24.0 on my primary monitor and 60.0 on my secondary results in "cinematic" visuals on the primary monitor and "soap opera" visuals on the secondary.

I'm currently using Windowmaker, but I see no reason why this wouldn't work with KDE.

[0] <https://news.ycombinator.com/item?id=48533247>

Maybe it's possible now. It wasn't back when I last used X. Now that Wayland is the default on most distros and works on nvidia now I don't see any reason to go back.

Good for you? But mixed-monitor DPI and mixed-monitor refresh rate haven't been key selling points of Wayland for like eight to ten years, at least.

It has been nearly eighteen years since the Wayland project started, and they are still not at feature parity with the major windowing systems. [0] It's nuts how long it's taking them. [1]

[0] As one example, apparently the Wayland policy for clients that stop responding for a few seconds and fill up their event mailbox is still to terminate the stuck client. If memory serves, Windows 9x handled stuck clients better than that.

[1] I'm sure it's good enough for what you're doing and you never run into any rough edges or misfeatures, so don't bother chipping in with that retort. ;)

I agree it used to be fiddly at best but in recent years I had found it to be pretty easy in X11.

I haven't had complaints there for Wayland but I will say that it breaking other things has been annoying.

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