New Apple Silicon M4 and M5 HiDPI Limitation on 4K External Displays

Post by smcleod » Mon, Mar 30, 2026, 6:21 AM UTC

TheTon wrote: post #23

tom_ wrote: post #14

Earlier quoted context omitted.

Yeah. I don't get it. If you've got a 3840x2160 display, intended use on macOS as a 1920x1080@2x display, what is the advantage of using a 7680x4320 buffer? Everything is drawn at twice the width and height - and then gets scaled down to half the width and height. Is there actually a good reason to do this? (I use my M4 Mac with 4K displays, and 5120x2880 (2560x1440@2x) buffers. That sort of thing does work, though i…

Yes 1920x1080@2x absolutely works on M4. I use this mode all day every day.

Post by smcleod » Mon, Mar 30, 2026, 6:31 AM UTC

TheTon wrote: post #19

TheCoreh wrote: post #9

Earlier quoted context omitted.

Yeah if I understand it correctly, this is more like 2160p@2x which is... unusual?

Yes, I would actually be surprised to learn that mode is available on any system. I’ve never seen that anywhere, though I only have a M1 Pro and an M4 Pro (and various Intel Macs). You’re rendering to a framebuffer exactly 2x the size of your display and then scaling it down by exactly half to the physical display? Why not just use a 1x mode then!? The 1.75x limit of framebuffer to physical screen size makes perfect…

Post by big_toast » Mon, Mar 30, 2026, 6:41 AM UTC

smcleod wrote: post #54

wmf wrote: post #5

This is not a normal retina configuration. This is a highly unusual configuration where the framebuffer is much larger than the screen resolution and gets scaled down. Obviously it sucks if it used to work and now it doesn't but almost no one wants this which probably explains why Apple doesn't care.

In my case it's a standard LG UltraFine 4K monitor plugged into a standard 16" M5 MacBook Pro via standard Thunderbolt (via USB-C) - not sure what's not normal about this? I've confirmed it with other monitors and M5 Macbook Pros as well.

Post by whatever1 » Mon, Mar 30, 2026, 7:05 AM UTC

brigade wrote: post #114

whatever1 wrote: post #13

How did none of the Apple devs notice this? 4k 32" inch is the industry standard for HiDPI monitors.

OP dances around the key context that this isn’t hidpi, but rather a 3rd party hack that uses hidpi rendering to supersample their “native” 4k resolution by 2x, since the end result looks more pleasing to them than the native 4k render.

Post by extr » Mon, Mar 30, 2026, 7:15 AM UTC

smcleod wrote: post #101

extr wrote: post #87

Earlier quoted context omitted.

If you actually care about this stuff you are going to run something like https://github.com/waydabber/BetterDisplay which easily allows for HiDPI @ 4K resolution, it does not "look bizarre" or "require fractional scaling". This is what the OP is about. I do the same thing, I run native res w/ HiDPI on a 27" 4K screen as my only monitor, works great.

Unfortunately BetterDisplay cannot set HiDPI @ 4K on the M5 machines - that was the first thing I tried.