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

https://smcleod.net/2026/03/new-apple-silicon-m4-m5-hidpi-limitation-on-4k-external-displays/
92•smcleod•1h ago

Comments

wronglebowski•49m ago
Props to the author for putting in what looks like ton of work trying to navigate this issue, shame they have to go to these lengths to even have their case considered.
MarcelOlsz•27m ago
I went to hell and back trying to get PIP/PBP monitors on my 57" g9 ultrawide to work with my M2 pro. ended up having to use a powered hdmi dongle, displaylink cable, and displayport, with 3 virtual monitors via betterdisplay. Allowing resolutions outside of macs limitations setting in BD is what did the trick. I don't envy OP. Having 5120x1440 @ lodpi was the worst, just ever so slightly too fuzzy but perfect UI size but eventually got a steady 10240x2880 @ 120hz with HDR. I literally laughed out loud when I read the title of the thread. Poor guy.
skullone•36m ago
I thought I was going crazy when my new m4 seemed "fuzzier" on my external 4ks. I tried replicating settings from my old MacBook to no avail. I wonder if Apple is doing this on purpose except for their own displays.
bsimpson•30m ago
Wouldn't HiDPI be 1080p@2x? Is that still available?
TheCoreh•23m ago
Yeah if I understand it correctly, this is more like 2160p@2x which is... unusual?
TheTon•9m ago
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 sense. Any more than that and you should just use the 1x mode, it will look better and perform way better!

armadyl•19m ago
Yeah I'm not sure what the point of this article is really or am I probably misunderstanding something? There's no such thing as 4K HiDPI on a 4K monitor. That would be 2160p @ 2x on an 8K monitor. 4K at 100% scaling looks terrible in general across every OS.
tom_•15m ago
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 if you sit closer than I do then you can see the non-integer scaling. Last time I tried a 3840x2160 buffer (1920x1080@2x), that worked. I am still on macOS Sequoia though.)

kalleboo•8m ago
> 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?

Text rendering looks noticeably better rendered at 2x and scaled down. Apple's 1x font antialiasing is not ideal.

Especially in Catalyst/SwiftUI apps that often don't bother to align drawing to round points, Apple's HiDPI downscaling has some magic in it that their regular text rendering doesn't.

TheTon•6m ago
Yes 1920x1080@2x absolutely works on M4. I use this mode all day every day.
wmf•28m ago
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.
nuker•24m ago
Send it to Tim Cook email. It worked for me fixing DisplayPort DSC bug. After Catalina, later MacOSes lost ability to drive monitors at higher than 60Hz refresh.

Apple support tortured me with all kinds of diagnostics, with WontFix few weeks later. Wrote email and it got fixed in Sonoma :)

https://egpu.io/forums/mac-setup/4k144hz-no-longer-available...

nerdsniper•10m ago
Thank you
PedroBatista•23m ago
Now I know I was not crazy and the "cheap" 4K screen I bought a couple months ago doesn't actually suck.

Tim Apple's Apple has been fu#$%& me again..

comex•20m ago
Well, it sounds like a real issue, but the diagnosis is AI slop. You can see, for example, how it takes the paragraph quoted from waydabber (attributing the issue to dynamic resource allocation) and expands it into a whole section without really understanding it. The section is in fact self-contradictory: it first claims that the DCP firmware implements framebuffer allocation, then almost immediately goes on to say it's actually the GPU driver and "the DCP itself is not the bottleneck". Similar confusion throughout the rest of the post.
xbar•12m ago
I think you are probably right--it's a real problem.

As an article, it is not 100% coherent, but there is a valid data and a real problem that is clear.

whatever1•18m ago
How did none of the Apple devs notice this? 4k 32" inch is the industry standard for HiDPI monitors.
MBCook•12m ago
Apple doesn’t make an 4k external monitor.

They’re likely all on Studio Displays.

mil22•12m ago
This would be even more compelling with screenshots with magnified detail insets showing the text blur.
pier25•8m ago
Is this for specific verisons of macOS?

The article doesn't mention it.

arjie•7m ago
I'm sure you've already given this a crack via some other technique (I just Cmd-F for it and didn't find) but I have had monitors with confusing EDIDs before that MacOS didn't handle well and the "screenresolution" CLI app https://github.com/jhford/screenresolution always let me set an arbitrary one. It was the only way to get some monitors to display at 100 Hz for me and worked very well for that since the resolution is mostly sticky.
LuxBennu•1m ago
Sadly I have the issue on a new m5 air. I have a 60hz 4k work monitor and two high refresh 4k gaming displays. The 60hz pairs fine with either gaming monitor, but the two gaming ones together and one just doesn't get recognized. Spent way too long trying new cables before realizing it's a bandwidth limitation.

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