Same display mirrored on two different dummies after sleep

[mickaelperrin]

Hi,

I have a setup with two identical displays (brand / model).

When I wake up from sleep, the two dummies are mirroring the same display, instead of mirroring their own associated display.

I need to quit and restart better display to get it working normally.

This is really annoying, any idea on how to fix that or a workaround ?

Note, this has already been reported as a comment of #553

Thanks,

[waydabber]

Not much fix for this, if two displays have the exact same identifiers and serial numbers, the OS can't tell them apart.

Generally if you'd like to have a two display setup, you have to try to make sure that you get them from a different manufacturing batches so their serial number is not identical (usually the same batch gets the same firmware with the same serial number). Of course getting from a different batch might increase the chance of differences in display panel colors which is not optimal for a multi-monitor setup. On some displays there might be a way to override the serial numbers, but this is rare.

#552 is I think different, since in that case the displays do not get confused so even if their vendor and model number are the same, their serial number is different. The issue reporter's problem seems to be the exact opposite.

See this discussion about a similar (but not exactly the same) situation: #944

[mickaelperrin]

@waydabber I am sorry but it looks like displays have each a different UUID. I use https://github.com/koekeishiya/yabai as my tiling window manager and I can effectively create rules to send apps to the proper display without issue.

Here is the display informations that the tool get:

yabai -m query --displays
[{
	"id":1,
	"uuid":"37D8832A-2D66-02CA-B9F7-8F30A301B230",
	"index":1,
	"frame":{
		"x":0.0000,
		"y":0.0000,
		"w":1680.0000,
		"h":1050.0000
	},
	"spaces":[1, 2, 3, 4, 5, 6]
},{
	"id":2,
	"uuid":"7F817989-055E-FE16-0857-D6964E3302DB",
	"index":3,
	"frame":{
		"x":-1242.0000,
		"y":-2160.0000,
		"w":3840.0000,
		"h":2160.0000
	},
	"spaces":[9, 10, 11, 12, 13, 14, 15, 16]
},{
	"id":27,
	"uuid":"788A66A3-73DE-63A5-C90B-A2661D91F570",
	"index":4,
	"frame":{
		"x":2598.0000,
		"y":-2160.0000,
		"w":2560.0000,
		"h":2880.0000
	},
	"spaces":[17, 18, 19, 20]
},{
	"id":28,
	"uuid":"96C9643F-EB3D-5615-9DE9-0966D8C1CFC8",
	"index":2,
	"frame":{
		"x":-3802.0000,
		"y":-2160.0000,
		"w":2560.0000,
		"h":2880.0000
	},
	"spaces":[7, 8]
}]

96C9643F-EB3D-5615-9DE9-0966D8C1CFC8 and 788A66A3-73DE-63A5-C90B-A2661D91F570 are the UUID of the two problematic displays.

Note also, that this issue didn't appear immediately.

And why is it working well when the app start but not after sleep ?

[waydabber]

You are indeed lucky! :)

(btw: I now see that you are using DisplayLink which is an added layer of complication, as the otherwise stable CGDirectDisplayID - CGDD ID on the screenshot - is changing continually, which triggers some kind of redetection in most display management apps that use it, including BetterDisplay. But since the UUID and serials are different, luckily the app is able to follow which display is which and should reassign settings to the new ID on the fly without issues.)

[mickaelperrin]

Yeah DisplayLink is my main motivation to upgrade my really nice M1 MBP. So sad, they only manage 1 display natively.

[waydabber]

Yes. Well if you do upgrade, you'll be able to use native smooth scaling with both displays and won't need dummy mirroring. :)

[mickaelperrin]

does it change anything in quality ? or is it only CPU usage related ?

[waydabber]

Quality should be marginally better (no banding artifacts for transparencies), it does not have some of the compatibility issues that affect dummy mirroring on some systems + display management is more straightforward as no mirroring and virtual screens are involved.