I'm confused about MacOS's scaled screen

[Fravin]

My MacBook Pro 13,3 (2017, TB, 256Gb) has a "default for screen" resolution.

In my experience with Windows, it looks like a scaled resolution for the tiny 13.3 LCD panel, maybe 125%. The "scaled" resolution to result in "more space" looks like a native resolution, or like Windows says "100%".

I'm concerned about the graphics performance, as a scaled resolution will struggle the GPU for more workload.

So, help me understand this thing. Does the "default for screen" envolves GPU scaling?

 

[leman]

Windows and MacOS handle resolution independence differently. In Windows, the OS instructs the applications that they need to scale their drawing to the screen, e.g. you have a 4K screen, if you draw everything 100% larger (200% DPI scaling), you get the same relative sizes as on a FullHD screen, but with more detail, since there are more pixels in between. MacOS instead uses supersampling. In HiDPI (or retina, if you prefer) mode, every logical point corresponds to exactly 2x2 pixels of the virtual screen. So a logical resolution of 1440x900 means having 2880x1800 pixels to draw to. A logical resolution of 1920x1200 means drawing to 3840x2400 pixels. The resulting image is then scaled to the actual resolution of your screen.

To answer your question: "default for screen" used to be 1440x900 logical points on a 15" MBP, so the final image would be 2880x1800 which perfectly maps to the display (no rescaling needed). Nowadays, Apple has bumped the default for screen to 1680x1050 logical points, or 3360x2100 pixels, which need to be downscaled to the 2880x1800 of the actual display.

That said, these things are optimised very well and dowscaling/upscaling should have no performance impact in themselves. Drawing to higher resolutions can have an impact if your apps draw a lot of things.

P.S. There is no official way to turn off the HiDPI mode on retina Macs. There are certain hacks and tools to activate these hacks though if you want to do that kind of thing.

 

[Fravin]

Thank you very much, leman.

Wondering if that logical resolution solution means faster responses for the user. I never figured out why PCs computers has less performance output in graphics with the same hardware.

Thank you!