HiDPI has always been perfectly supported by X11.

The only problem that has existed is that originally there was a single DPI value, not a different DPI value for each monitor.

This has never created any problem for the people using multiple monitors with the same resolution, but only for the people who have used multiple monitors having different resolutions and who might have not liked the changes in windows size when moving a window from a monitor to another monitor.

That was indeed a problem, but it really affected a rather niche use case and it was also trivial to solve without any change in the X11 design, by just making DPI a per monitor variable, which was done long ago.

So criticizing X11 about a supposed problem with HiDPI is incorrect. I have used only multiple 4k monitors with my PCs, with X11, for more than a dozen years and I never had any problem with HiDPI, with the exception of many Java programs written by morons, which ignore the system settings and which also do not allow the user to change the font used by them. I do not know which is the problem with the Java programmers, but I never encountered programs with such a behavior, except those written in Java. Moreover, the Java programs are also the only that had problems with monitors using 10-bit per color component.

While X11 itself never had problems with supporting HiDPI, at least not in the XFCE that I am using, I heard that other desktop environments have created problems with HiDPI that have nothing to do with X11, by not exposing the X11 DPI settings but providing instead some "window scaling" settings, which is something that I do not know how it is implemented, but there are good chances that it is implemented in a wrong way, judging from the complaints that I have seen. I cannot imagine how one could use correctly a "window scaling" factor, because the font rendering program must know the true DPI value when rendering for instance a 12-point font. If rendering is done at a wrong DPI and then the image is scaled, the result is garbage, so in that case it would not be surprising that people claimed that HiDPI works badly in X11, when in fact it was Gnome or whatever desktop environment was used who was guilty for bad support, not X11. I never had to fight with those desktop environments, but I assume that even those would have worked correctly with HiDPI, when using xrandr to configure X11, instead of using the settings of the desktop environment.

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izacus 15 hours ago | parent [-]

There is nothing "niche" about plugging in a modern (e.g. made within last 5 years) laptop into an external display.

These kind of posts just show how disconnected from reality some of y'all are from what most Linux desktop users nowadays actually need from the desktop platform.

	▲	adrian_b 15 hours ago \| parent [-]
		I always plug my laptop into one or two external displays. Even without configuring distinct DPIs per monitor that was not a problem for me, because on the small screen of the laptop I kept only some less important application, like the e-mail program, while working on the bigger external displays, so I had no reason to move windows between the small screen of the laptop and the bigger external displays. But like I said, setting a different DPI value for each monitor has been added to X11 many years ago, I do not remember how many. I do not see why one would want to move windows between the external displays and the laptop, when you have connected external displays, so I consider this a niche use case, i.e. moving windows between small screens and big screens. I agree with you that having simultaneously big screens and small screens is not niche, so I was not referring to this. Without a per-screen DPI value you cannot control the ratio between the sizes of a window when is moved between the big screen and the small screen, but even when you control the ratio, moving windows between screens of different sizes does not work well because you must choose some compromise, e.g. if you keep the same physical size some windows from the big screen will not fit on the small screen and if you make the windows occupy the same fraction of the screen size they will change their sizes during moving and they will be more difficult to use on the small screen. But like I have said, this no longer matters as the problem has been solved even for this niche use case. I do not even remember if this problem still existed by the time when Wayland became usable.