DELL U4021QW can't get above 150% HiDPI

[sam-mfb]

I have a DELL U4021QW with a native resolution of 5120x2160. On 1.x.x, using dummy displays, I was able to configure HiDPI resolutions of uneven multiples, in particular, 4096x1728.

On 2.x.x (which is otherwise awesome), using smooth scaling, I seem to be limited to HiDPI resolutions of 150% or less. I can get 3840 x 1620 (150%) fine, but nothing else. I can force these other resolutions as LoDPI, but they don't look as nice. Is there a way to get HiDPI between 150% and 200%? I've played around with the different smooth scaling options, but can't seem to get those to turn on.

This is particular odd because I have another external monitor attached with a native 4096x2160 resolution (4K) and it has no problem giving me HiDPI resolutions of any percentage up to 200%.

This is on a Mac Studio M1 running Ventura (13.4.1(c))

[sam-mfb]

To illustrate, compare (no resolutions past 3840x1620, i.e., 150%):

with (all resolutions up to native - 3840x2160):

[waydabber]

Hi there - the problem is the max framebuffer limit of 7680px (3840px HiDPI) for Pro/Max/Ultra Apple Silicon Macs. This means you have HiDPI scaling options up until you reach 3840px HiDPI width (7680px framebuffer width) and then a gap and the next resolution you can get is the native resolution (in LoDPI) which has a width of 5120px in your case.

You can try using virtual screen streaming to circumvent this issue (or mirroring - both have various disadvantages over the native solution).

[sam-mfb]

ohhhh. that's a shame. I was sort of used to my old resolution, even though its only a few pixels bigger. But I'm not sure I can give up apple watch unlocking in 2.x.x (which wouldn't work if i was streaming, which is what i had to do on 1). I may just have to live with 3840px....

[sam-mfb]

Not that it really matters, but I've decided to stick with 150% (3840 HiDPI). I like having my login screen and Apple Watch unlock back. Really nice job on version 2.

[waydabber]

Yes, sticking to the native option is understandable. :)

[maxiedaniels]

@waydabber Hmm super interesting.. this is kinda stopping me from getting that Dell monitor. Do you know if the new frame buffer limit is going to be changed in any newer Mac's? Or has it been with m3 systems? I'm on an M1 Max but might upgrade soon.

I'm confused about this anyway - if the limit is 7680, so 3840 HiDPI, that's a 2x amount. Does all HiDPI have to be 2x?? My monitor runs at 3008x1692, so is it actually running at 6016x3384? I assumed scaling can be 1.6x, or other lower than 2x values.

[waydabber]

There are multiple limits, but the absolute one is 3072px for entry level and 3840px for pro level. We will see whether the M4 family changes anything. I don't think though as macOS on Apple Silicon simply starts glitching beyond 8K resolution (which can be achieved using virtual screen mirroring), even the Messages app can't properly open (as well as other Catalyst apps) - I guess if Apple would have tested resolutions beyond this, we'd have seen some improvement in this department.

[maxiedaniels]

@waydabber How do you check the frame buffer limit? Terminal command or more complicated than that?

[waydabber]

It's listed under Display Information.../Capabilitites under the display in the app.

[aequitas]

@waydabber I found this thread as it seems related to my problem. I have a U4021QW connected to a MacBook Pro M4 Pro. When I look at the capabilities it shows 3840 as horizontal limit [0], however I can't select 3840x1620 as a HiDPI resolution[1], maximum I can select is 3360x1418. What could be wrong?

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