From what I understand, the main goal is to fix the problem that non-native (1:1 pixel mapping) resolutions and scaling look worse than native. This is a problem when you ship high-dpi displays that need UI scaling in order for things to be readable. Apple's solution was to render everything at a higher, non-native resolution so that images were always downscaled to fit the display.

So to oversimplify, Windows can have a problem where if you are running 1.5X scaling so text is big enough, you can't fit 4K of native pixels on a 4K display so videos are blurry. If instead you were rendering a scaled image to a 6K framebuffer and then downscaling to 4K, there would be minimal loss of resolution.

I do not know who was the moron that first used scaling in conjunction with displays having a higher resolution, but this is a non-solution that should have never been used anywhere.

Already more than 35 years ago the correct solution was used. For text and for graphics, the sizes must be specified only in length units, e.g. in typographic points or millimeters or inches, e.g. by configuring a 12-point font for a document or for an UI element. Then the rasterizer for fonts and for graphics renders correctly everything at a visual size that is independent of the display resolution, so it is completely irrelevant whether a display is HiDPI or not.

To combat the effect of rounding to an integer number of pixels, besides anti-aliasing methods, the TTF/OTF fonts have always included methods of hinting that can produce pixel-perfect characters at low screen resolutions, if that is desired (if the font designer does the tedious work required to implement this). Thus there never exists any reason for using scaling with fonts.

For things like icons, the right manner has unfortunately been less standardized, but it should have been equally easy to always have a vector variant of the icons that can be used at arbitrary display resolutions, supplemented by a set of pre-rendered bitmap versions of the icons, suitable for low screen resolutions.

I am always astonished by the frequent discussions about problems caused by "scaling" on HiDPI displays in other operating systems, because I have been using only HiDPI displays for more than a dozen years and I had no problems with them while using typefaces that are beautifully rendered at high resolution, because I use X11 with XFCE, where there is no scaling, I just set the true DPI value of the monitors and everything works fine.

> From what I understand, the main goal is to fix the problem that non-native (1:1 pixel mapping) resolutions and scaling look worse than native.

That would be my instinct as well, but the author seems to be delibarately doing the exact opposite. Trying to force a 2x HiDPI and then downscaling to native display resolution whereas he could have just done a 1:1 LoDPI rendering. What you get in the end is some equivalent of hack/brute-force smoothing/antialiasing of what was rendered in the downsample.