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

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

#51

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.

Thanks, it was a good portion of my weekend bashing my head against the keyboard trying to figure out what was going on and if there was a workaround I could use (there isn't that I've found).

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

#52
TFA doesn't say -- does anyone know if this applies to 5k and 6k monitors? On my 5k display on a M4 Max, I see the default resolution in system settings is 2560x1440. Which is what I'd expect.

If the theory about framebuffer pre-allocation strategy is to hold any water, I would think that 5k and 6k devices would suffer too, maybe even more. Given that you can attach 2x 5k monitors, the pre-allocation strategy as described would need to account for that.

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

#53

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

Not in the Apple world, and this article is centered on Apple. https://bjango.com/articles/macexternaldisplays/ - 24" you need 4k - 27" you need 5K. - 32" you need 6k. Windows subpixel aliasing (Clear Type) manages a lot better with lower pixel density. Since Windows still has a commanding market share in enterprise, you might be right about the industry standard for HiDPI but for Apple-specific usage, not really.

This still baffles me. Never mind Windows; I can get sub-pixel font rendering with the ability to fine-tune it on virtually any major Linux distro since around 2010.

Meanwhile, Apple had this but dropped it in 2018, allegedly under the assumption of "hiDPI everywhere" Retina or Retina-like displays. Which would be great...except "everywhere" turned out to be "very specific monitors support specific resolutions".

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

#54
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.

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

#55
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 built-in or first-party displays, it tells you this could hurt performance because thats exactly what the OS is going to do to give you more space without making text unreadable aliased fuzz, it renders the "apparent" resolution pixel doubled, and scales it down which provides a modicum of sub-pixel anti-aliasing's effect. Apple removed subpixel antialiasing a while back and this is the norm now.

I have a 4K portable display (stupid high density but still not quite "retina" 218) on a monitor arm I run at, as you suggest, 1080p at 2x. Looks ok but everything is still a bit small. If you have a 4K display and want to use all 4K, you have the crappy choice between making everything look terrible, or wasting GPU cycles and memory on rendering an 8K framebuffer and scaling it down to 4K.

I'm actually dealing with this right now on my TV (1080p which is where I'm writing this comment from). My normal Linux/Windows gaming PC that I have hooked up in my living room is DRAM-free pending an RMA, so I'm on a Mac Mini that won't let me independently scale text size and everything else like Windows and KDE let me do. I have to run it at 1600x900 and even then I have to scale every website I go to to make it readable. Text scaling is frankly fucked on macOS unless you are using the Mac as Tim Cook intended: using the built-in display or one of Apple's overpriced externals, sitting with the display at a "retina appropriate" distance for 218ppi to work.

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

#56

TFA doesn't say -- does anyone know if this applies to 5k and 6k monitors? On my 5k display on a M4 Max, I see the default resolution in system settings is 2560x1440. Which is what I'd expect. If the theory about framebuffer pre-allocation strategy is to hold any water, I would think that 5k and 6k devices would suffer too, maybe even more. Given that you can attach 2x 5k monitors, the pre-allocation strategy as desc…

I believe it will, it won't be until you push up to an 8k display that you'll get the old level of scaling back (could be wrong though as I don't have a way to test this).

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

#57
post #15

This would be even more compelling if you included screenshots with magnified detail insets showing the text blur.

Thanks for the feedback, I'll try to take some photos, it's not an easy thing to do accurately without a good camera setup, but I'll reply here after work if I get something setup and added to the post.

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

#58
post #34

Earlier quoted context omitted.

No, it didn’t get fully fixed. Fucking with DP 1.4 was how they managed to drive the ProDisplay XDR. If your monitor could downgrade to DP 1.2 you got better refresh rates than 1.4 (mine could do 95Hz SDR, 60Hz HDR, but if my monitor said it could only do 1.2, that went to 120/95 on Big Sur and above, when they could do 144Hz HDR with Catalina). I would be absolutely unsurprised if their fix was to lie to the monitor…

Ahh, true, I now have 120Hz top, but it's fine, why I said fixed :) I now recall in Catalina I had full 144Hz and VRR options! Monitor is Dell G3223Q via Caldigit TS4 DP.

I was using 2 27" LG 27GM950-Bs (IIRC), that could do up to 165Hz and VRR on a 2019 cheesegrater Mac Pro, wasn't the cables, or the monitors, or the card.

People at the time were trying to figure out the math of "How did Apple manage to make 6K HDR work over that bandwidth?" and the answer was simply "by completely fucking the DP 1.4 DSC spec" (it was broken in Big Sur, which was released at the same time). The ProDisplay XDR worked great (for added irony, I ended up with one about a year later), but at the cost of Apple saying "we don't care how much money you've spent on your display hardware if you didn't spend it with us" (which tracks perfectly with, I think, Craig Federighi spending so much time and effort shooting down iMessage on Android and RCS for a long time saying, quote, "It would remove obstacles towards iPhone families being able to give their kids Android phones").

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