How the heck do you have a 1080 Ti running? I assume the machine is still running High Sierra before Web Driver support was dropped?
That capture is from High Sierra indeed. I am now running Radeon VII. And I am too lazy to make another screen capture / comparison to illustrate difference of fonts rendering between HiDPI and non HiDPI environment.
The following capture was created during the testing of RadeonBoost. But anyway, it also captured the resolution’s info. In my case, that’s defaulted to use HiDPI rendering.
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Could you elaborate this more about using higher resolution than what monitor is specified?
There is no absolute relationship between rendering resolution, and the “UI looks like” resolution, and the actual monitor's resolution.
For macOS, the HiDPI mode always render at 2x the UI looks like resolution.
e.g. For 3840x2160 monitor.
If you choose 3840x2160 in system preferences, that means everything render at 1x scale in 3840x2160. For normal size monitor (e.g. 27"), everything will be very small to read.
If you choose 1920x1080 HiDPI, that means everything still render at 3840x2160, however, in 2x scale. Everything will looks 2x bigger. Therefore, you are still fully utilise all 3840x2160 pixels on the monitor, but the "UI looks like" 1920x1080 (in size).
If you choose 2560x1440 HiDPI, then everything will be render at 5120x2880, then down scale back to 3840x2160. You are still fully utilise all 3840x2160 pixels. But the UI looks like 2560x1440, and the macOS actually render the desktop at 5120x2880, which is higher than your monitor's resolution.
In fact, you can also choose 3840x2160 HiDPI. So that the GPU render everything at 8k, then downsample back to 4k, and display at 4k. In most cases, this is just a waste of the resources (e.g. VRAM). But if you connect the Mac to a large size 4k TV (e.g. 84”), this setting can be useful to make the images (e.g. fonts) looks better.
In my case, the macOS render everything at 2x the monitor resolution. Then down scale back to the native resolution. This makes the fonts looks much better (also make the screen capture, and the "zoom in" image looks much better).
From memory, OSX has this function since Mavericks.