alt Hacker News> then the final result is raster-scaled with some sinc/Lanczos algorithm back down to the physical resolution. This shows up as ringing artifacts, which are very obvious with high-contrast, thin regions like text.
I don't think this is true. I use non-integer scaling on my Mac since I like the UX to be just a little bit bigger, and have never observed any kind of ringing or any specific artifacts at all around text, nor have I ever heard this as a complaint before. I assume it's just bilinear or bicubic unless you have evidence otherwise? The only complaint people tend to make is ever-so-slight additional blurriness, which barely matters at Retina resolution.
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> ringing or any specific artifacts at all around text
There are a few Reddit threads that crop up when one searches for 'macOS ringing artifacts scaling'. For instance, these ones:
https://www.reddit.com/r/macbookpro/comments/1252ml8/strange...
https://www.reddit.com/r/MacOS/comments/1ki58zk/fractional_s...
https://www.reddit.com/r/MacOS/comments/l8oadr/macos_fringin...
All are ringing artifacts, typical of downscaling. I no longer have a Mac (chose one for work to try it out, saw this issue, returned it immediately), but I assure you this is what happens.
> The only complaint people tend to make is ever-so-slight additional blurriness
At no scale factor should there be any blurriness unless a framebuffer resolution is explicitly set. The 'scale factor' should be entirely independent of the physical resolution, which macOS simply does not do.
Apple's understanding and implementation of 'Retina' comes from a singular source: the straightforward doubling in each dimension of the display resolution of the iPhone 4 compared to the iPhone 3GS. It has not changed since, and has applied this algorithm throughout its OS stack.
Indeed, these artifacts sound like they're coming from Display Stream Compression [1] rather than scaling. I've had Macs occasionally use DSC when it wasn't necessary; power-cycling the display and/or changing the port it's plugged into usually fixed it. If it's consistently happening, though, it's probably because the display, the cable, the port, and/or the GPU can't handle the resolution and refresh rate at full bandwidth.
[1]: https://en.wikipedia.org/wiki/Display_Stream_Compression