What does "Set as Main Display" do?

[CeKMTL]

I'm a payed customer of BetterDisplay; thank you for this wonderful app.

There's an issue with virtual screens where only the first virtual screen attached to built-in display works as expected. If you add another one then it starts to behave erraticly and ends up mixing the virtual displays to only the first virtual display so for example:

You have 3 virtual displays (all attached to Built-in display); first virtual display works as expected, second virtual display points to #1 and third virtual display points to #1 and they all show the contents of #1. This does not happen (usually) when using PiP, only when doing "Set as main display".

So to recap; Main built-in display works OK. Virtual screen #1 works Ok. Virtual screen #1+n end up in a mess pointing to #1.

Why do I need multiple virtual screens?
I own a MBP M4 MAX 128Gb (latest Sequoia 15.5 (24F74)) and do demos outside of office so usually I have to close/quit all my 12+ desktops (webpages/emails/jira/confluence/banking/documents/IDE/etc...) as they contain sensitive information that I don't want ppl to see. My idea is to compartimentalize these different groups of desktops to virtual screens all attached to built-in laptop screen and be able to change to them or hide them so if I'm out and about doing a demo, only the "Demo" virtual screen is shown as the "main" one and the rest are hidden.

I would also like for BetterDisplay to have some option to be able to define direct keyboard shortcuts to toggle "main" between different virtual screens and when toggling to a virtual screen (or built-in one), to have the cursor/mouse pointer centered in the middle of the selected virtual (or built-in) screen. For now I use "CatchMouse" app (that is 10+ years old) to achieve this with a keyboard shortcut.

An interesting data point is that with "CatchMouse" app which has config to enter up to 4 "Display Shortcut", even with 4 screens (1 built-in + 3 virtual), the only two "Display Shortcut" that work are Display 1 for built-in and Display 2 for Virtual #1/2/3/n ...

This has been tested with app version 3.5.5 & Version 3.5.6 Internal Pre-Release Build 40766.

For the time being, I've settled for having only one virtual screen where I put the "demo apps" in and the rest is in the Built-in screen and switch back & forth between them with "set as main screen" and "CatchMouse" for the mouse pointer.

After many hours of trying different combinations, I thought of opening this ticket to see if what I'm trying to achieve is possible and/or quick to fix/implement.

If you need any other information, please don't hesitate to contact me.
Thank you.

[waydabber]

Hi - just to clarify: by "virtual display" you mean Picture in Picture window - so the PIP window shows the wrong virtual screen after changing the main status of a display?

[waydabber]

About the set main keyboard shortcut: you can use the macOS Shortcuts app with a Set Screen as Main action provided by BetterDisplay, and then assign a keyboard shortcut to it.

[CeKMTL]

Hi!

(2) Yes I already did that and thanks to the CatchMouse app I can move the mouse pointer to the center of the screen be it the built-in screen or the virtual one. It would be great if BetterDisplay had this functionality so I could use it with shortcuts instead of sending a global keyboard shortcut to trigger CatchMouse and move the mouse pointer accordingly. As for the "Set Screen as Main" that is exactly what I use in shortcuts: 1) Set Virtual - 1 as main. 2) Send Keyboard combination "Cmd+Opt+2".

(1) The problem happens when you create more than 1 virtual screens on the laptop that are attached to the Built-in screen.
You can try it yourself:

• Create 3 virtual screens of same resolution as Builtin screen and attach them to builtin screen but do not start automatically screen mirroring or pip.
• Make Virtual Screen 1 the MAIN screen.
• Add 2 desktops and launch some apps there so you know that it is Virtual #1
• Make Virtual Screen 2 the MAIN screen.
• You will see that it is exactly the same as Virtual Screen #1 (you won't see Virtual screen 2 contents).
• Repeat same for 3 and you will see 1 contents.
  If you then go to Builtin Display and make it main, you will see it's contents correctly as expected.
  You can then launch PiP for Virtual Screen 2 and inside PiP you will see correct contents of Virtual Screen 2 (which is not the case when you don't use PiP and instead use "Set as MAIN".

So to recap: Only Virtual Screen 1 works & displays contents of Virtual Screen 1 when using "Set as MAIN display".

Thank you!

[waydabber]

Ok. So the issue is not related to PIP windows or streaming? What do you exactly mean by "attach them to builtin screen"?

[CeKMTL]

Correct, does not fail in PiP or Streaming, only when you change the target screen to "Set as Main Display".

[waydabber]

Since virtual #1 is invisible (it exists in the memory only), when you make it main, it should not have a clear effect, you - still see your built-in display on your display, not virtual #1 - the only difference is that in the display layout virtual #1 will behave as the main display and the system will relocate all windows on the previous main display to the new main display. Also, some apps will launch on the new main display by default (invisibly) instead of the built-in display which is then not a main display anymore, but acts as an extended display.

In other words, the "Set as Main Display" is not to make a virtual screen visible on your real display - it just tells macOS that you want a particular (real or virtual) screen to be the main display in a multi-display layout as opposed to be an extended display. In the past only the main display had the menu bar and dock, but in modern macOS versions, if "Displays have separate spaces" is enabled in System Settings (which is the case by default), even non-main displays can have the menu bar and dock and can hold multiple spaces - which makes understanding the role of the main display a bit difficult (note: technically the main display has the origin coordinate set to (0;0), but of course users are not aware of this).

[CeKMTL]

Mostly yes but i don't think it swaps contents as the (number of) desktops are distinct and specific for each screen as in my current setup right now I have:

• Built-in Screen with 10 Desktops.
• Virtual Screen 1 with 5 Desktops.
  The change is instantenous and everything is exactly in place.

[waydabber]

Yes. Switching the main display will swap spaces as well. The idea is that when you are using your MacBook with the built-in display as the main display but then you connect your external display which then becomes the main display and the MBP display be the secondary (or go missing in clamshell mode), you can continue everything as the new main display seamlessly. So all spaces and windows are moved over to the new display and resizable windows are resized proportionally to fit the new display dimensions.

[CeKMTL]

Great. So circling back to the initial question; only first virtual screen works as expected. Is it an OS limitation or can BetterDisplay do something about it/manage it?

[waydabber]

The way main displays work is built into macOS so the app can't change that if this is the question. :(

[CeKMTL]

Ok, I see.
Thank you.