[vetinari]

macOS doesn't expose fractional scaling to applications, it is done by the output encoder by scaling the entire framebuffer. For software, it is strictly integer only.

It is also careful with the resolutions it supports, it is not just any random scale requested. It is always to scale down, but not lose many pixels. For example, with 2560x1600 physical display (rMBP13), you can go to logical 2880x1800 (@1.78 scale) or 3360x2100 (@1.52 scale), but not further.

With Linux (and also Windows), people have weird requests that would not fly in macOS world.

[emersion]

>macOS doesn't expose fractional scaling to applications, it is done by the output encoder by scaling the entire framebuffer. For software, it is strictly integer only.

Wayland works the same way.

[vetinari]

I haven't looked into the sources, but my impression was, that it was using GPU to scale surfaces and then compose into final framebuffer, that is the same resolution as display. Not that it uses output encoder.

The quick test is, when I do a screenshot, I get a file with dimensions same as physical display, not logical resolution. On macOS, it is exacly the other way.

Scaling with GPU is more flexible; you can do things per surface instead of per desktop; but slightly more complicated (because you do things per surface instead of per desktop), takes away GPU capacity/memory bandwidth from applications when then might it, and is more power hungry when the GPU could be idle.

[floatboth]

That's up to the compositor, but pretty much everyone does it per surface indeed.

What everyone means by "it's like macOS" is that the same "render at ceil(scale) and downscale" general principle is used.

[izacus]

And that is an ok solution as well - something Wayland or other Linux compositors can't do and force you to be stuck in either "too tiny" or "too large" uncanny valley of UIs.

[vetinari]

Because Linux and Windows users ask for different things than Mac users.

With 2560x1440 display, you won't get fullhd@2x sized desktop (scale 133%) on Apple. That something expected in Linux or Windows, but Apple will get you at most 1680x1050@2x (152%, they're 16:10, so different height) here.

It is compounded by the issue, that Apple traditionally used 72 dpi for @1x scale, while Windows and Linux used 96 dpi. Apple apps look quite good at lower resolutions, while Linux (ok, Gnome) dug itself into a hole and looks good on dpis much higher than 96. For Apple, it is acceptable to run 2880x1900 or 3360x2100 on 2560x1600 display, but when Gnome looks passable on 1600x900@1x, good on 1920x1080@1x and you've got 2560x1440, so you need to display 4K (1920x1080@2x) logical resolution on that... that's more "interesting".

[floatboth]

Pretty much all Wayland compositors support fractional scaling with independent scales for different monitors.