What's the deal with display scaling?

[dfee]

I bought a new 2018 15" MBP and for the first time I'm dealing with the concept of "display scaling".

And on my new "LG UltraFine 4K Display":

So the point is, I get more screen "real estate" when selecting "more space" and more "per-pixel density" using "larger text".

But I'm not clear as to what this actually means. For instance, the "more space" setting for my 4k display says it "Looks like 2560 x 1440". But it's a "4096-by-2304" display! OK, so everything is upscaled by 60%? Here are the other factors:

4k Display
2560x1440: 1.6 upscale (aka "More Space")
2304x1296: 1.77 upscale
2048x1152: 2 upscale
1680x945: 2.44 upscale
1280x720: 3.2 upscale (aka "Larger Text")

15" MBP Display
1920x1200: 1.5 upscale (aka "More Space")
1680x1050: 1.71 upscale (aka "Default")
1440x900: 2 upscale
1280x800: 2.25 upscale
1024x768: 2.8 upscale (aka "Larger Text")

But in a strange way I've noticed that it's actually a bit less "fluid". Applications like VSCode (perhaps because it's an Electron app?) perform a bit differently (in terms of UI and font sizing) at the different resolutions. For example, VSCode doesn't let my screen go below 9px for a font (which is desirable when using the 2x scale (2048x1152) on a 4k display (trying to capture the sort of feel for an individual application as if it were running in a "More Space" format).

I've also seen mentions of battery life across the internet when using the MBP at a non-default scaling. But practically speaking, am I wasting the quality of the display my 15" MBP display if I set it's virtual resolution at "1920x1200"?

Does this impact how videos (Firefox showing a YouTube video for example) are actually rendered? I.e. do they see that my computer can / cannot handle a true 1080p video?

 

[afir93]

For instance, the "more space" setting for my 4k display says it "Looks like 2560 x 1440". OK, so everything is upscaled by 60%? Here are the other factors:

4k Display
2560x1440: 1.6 upscale (aka "More Space")
2304x1296: 1.77 upscale
2048x1152: 2 upscale
1680x945: 2.44 upscale
1280x720: 3.2 upscale (aka "Larger Text")

15" MBP Display
1920x1200: 1.5 upscale (aka "More Space")
1680x1050: 1.71 upscale (aka "Default")
1440x900: 2 upscale
1280x800: 2.25 upscale
1024x768: 2.8 upscale (aka "Larger Text")

Pretty much this, except that it's not "upscaled" in the classical sense (as this implies that the screen is only rendered in, say, 2560x1440 and this is "stretched out" to 4K with the intermediate pixels being interpolated), but that everything you see on-screen is rendered at a higher resolution accordingly. The thing to consider here is that your Mac will operate at Retina resolution whenever possible, which is why Apple calls it "looks like x times y" and not "x times y resolution". Meaning that the lower the "looks-like" resolution is, the sharper all the on-screen content and elements will be, while going for a higher "looks-like" resolution will have the pixel density in relation to the on-screen elements reduced, in other words there is more space on-screen because everything looks less sharp.

The default is either x2 (which looks the "best" or cleanest in the sense that every pixel of the lookalike-resolution corresponds to exactly four actual pixels on-screen) or a setting slightly below that (on the case of the MacBooks I believe, to make for more room on-screen). So the resolution definitely isn't wasted if you set it to, say, "look like"-1080p on a 4k screen.

Videos you see in web browsers and the like usually display in the highest resolution that the size of its player window allows for, independently of what the scaling in System Preferences is, it will stick to the "true" resolution and fully exhaust that.