New Apple Silicon M4 and M5 HiDPI Limitation on 4K External Displays • Hacker News Board

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

#81

Post by petersellers » Mon, Mar 30, 2026, 5:01 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.

In macOS display settings, what scaling mode are you using? This bug appears to only affect 4K monitors that are configured to use the maximum amount of screen space (which makes text look uncomfortably tiny unless you have a very large monitor). Most people run at the default setting which gives you the real estate of a 1080p screen at 2x scale, hence the "not normal" part of this configuration.

Actually, I don't even think it's possible to run HiDPI mode at the native resolution scale from within the macOS settings app, you'd need something like `Better Display` to turn it on explicitly.

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

#82

Post by toxik » Mon, Mar 30, 2026, 5:02 AM UTC

wpm wrote: post #55

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.

This is what us proles on third-party monitors have to do to make text look halfway decent. My LG DualUps (~140ppi if I recall) run at 2x of a scaled resolution to arrive at roughly what would be pixel-doubled 109ppi, which is the only pixel density the UI looks halfway decent at. It renders an 18:16 2304 x something at 2x, scaled down by 2. It's also why when you put your Mac into "More Space" resolution on the buil…

Pedantry: 18:16 is the same as 9:8 since it's a ratio.

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

#83

Post by [deleted] » Mon, Mar 30, 2026, 5:02 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.

[deleted]

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

#84

Post by jval43 » Mon, Mar 30, 2026, 5:03 AM UTC

Not again! Had these issues with 2016 Macbook Pro (the touchbar one).

That one also wasn't a hardware limitation as it ran my displays just fine in bootcamp, but macOS would just produce fuzzy output all the way.

It's infuriating.

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

#85

Post by Rohansi » Mon, Mar 30, 2026, 5:08 AM UTC

eptcyka wrote: post #73

sgerenser wrote: post #29

Earlier quoted context omitted.

I don’t know why this was downvoted, I agree that this is a highly unusual configuration. Why render to a frame buffer with 2x the pixels in each direction va the actual display, only to then just scale the whole thing down by 2x in each direction?

Because Apple no longer implements subpixel rendering for fonts?

Supersampling the entire framebuffer is a bad way to anti-alias fonts. Especially since your font rendering is almost certainly doing grayscale anti-aliasing already, which is going to look better than 2x supersampling alone. And supersampling will not do subpixel rendering.

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

#86

Post by not_your_vase » Mon, Mar 30, 2026, 5:08 AM UTC

harikb wrote: post #72

krackers wrote: post #70

Earlier quoted context omitted.

This needs a story. What did you say to him?

He was told, he had a call from Pope

Heh, classic Mike (not the Pope one)

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

#87

Post by extr » Mon, Mar 30, 2026, 5:09 AM UTC

compounding_it wrote: post #35

The ideal work/coding resolutions and sizes for macOS that I would suggest if you are going down this rabbit hole. 24 inch 1080p 24 inch 4k (2x scaling) 27 inch 1440p 27 inch 5k (2x scaling) 32 inch 6k (2x scaling) Other sizes are going to either look bizarre or you’ll have to deal with fractional scaling. Given that 4k is common in 27/32 inches and those are cheap displays these kinds of problems are expected. I hav…

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.

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

#88

Post by extr » Mon, Mar 30, 2026, 5:09 AM UTC

tern wrote: post #77

compounding_it wrote: post #35

The ideal work/coding resolutions and sizes for macOS that I would suggest if you are going down this rabbit hole. 24 inch 1080p 24 inch 4k (2x scaling) 27 inch 1440p 27 inch 5k (2x scaling) 32 inch 6k (2x scaling) Other sizes are going to either look bizarre or you’ll have to deal with fractional scaling. Given that 4k is common in 27/32 inches and those are cheap displays these kinds of problems are expected. I hav…

Yup, 27" 4k with a Mac is truly awful. Don't do it. Get a 5k display.

Disagree completely. Works great for me.

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

#89

Post by tgma » Mon, Mar 30, 2026, 5:10 AM UTC

This might be a dumb question: Is the author looking to run 4k display at HiDPI 8k framebuffer and then downscale? What's the advantage of doing so versus direct 4k low-DPI? Some sort of "free" antialiasing?

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

#90

Post by smcleod » Mon, Mar 30, 2026, 5:12 AM UTC

petersellers wrote: post #81

smcleod wrote: post #54

Earlier quoted context omitted.

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.

In macOS display settings, what scaling mode are you using? This bug appears to only affect 4K monitors that are configured to use the maximum amount of screen space (which makes text look uncomfortably tiny unless you have a very large monitor). Most people run at the default setting which gives you the real estate of a 1080p screen at 2x scale, hence the "not normal" part of this configuration. Actually, I don't ev…

If you use the middle screen scaling you're given absolutely huge UI elements and it's the case for the inbuild 16" screen as well as external displays but when you get up to 32" displays it's almost comical how large the UI is on the middle / default setting.