alt Hacker News> I assume the dearth of other options was because macOS doesn't do fractional scaling
Except it does? I have a 14" MBP with a 3024x1964 display. By default, it uses a doubling for an effective 1512x982, but I can also select 1800x1169, 1352x878, 1147x745, or 1024x665. So it certainly does have fractional scaling options.
If you connect a 4k 2160p monitor, you can go down or up from the default 1080p doubling (https://www.howtogeek.com/why-your-mac-shows-the-wrong-resol...). If you select 2560x1440 for a 4k 2160p screen, that's 150% scaling rather than 2x (https://appleinsider.com/inside/macos/tips/what-is-display-s..., see the image where it compares "native 2x scaling" to "appears like 2560x1440").
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I believe it was 2x only early on. But as you said it’s fractional now and has been for a longtime.
The instant Apple wanted to use a panel that wasn’t 2x, the feature appeared.
macOS fakes fractional scaling by rendering a larger image at 2x and then downscaling it. For example, 1800x1169 renders a 3600x2338 at 2x scaling, then resizes the rendered image to 3024x1964. This is slower and looks worse than true fractional scaling would be, but makes the implementation a lot easier and in practice it’s hard to tell the difference. It’d look pretty awful if the native ppi wasn’t so high.