When Stage Manager is enabled, AltTab doesn't show thumbnails for windows not shown in SM's stack

[ypekka]

The bug

When the Stage Manager is active and there is a screen west (left) of main screen only those window's previews are captured that are on Stage Manager's recent list. All other windows do not have previews visible. If Stage Manager is deactivated the issue resolves.

If screen arrangement is modified so that the screen in the west is moved more towards WNW or WSW and screens overlaps less than about 50% then again the issue resolves.

Screen on the west can be either physical or virtual (like BetterDisplay) and resolution or orientation doesn't seem to affect the issue.

Environment

• AltTab version: 6.64.0
• macOS version: 14.2.1

[lwouis]

Could you please share a video of the issue? It's hard for me to understand the issue from your description.

Thank you 🙇

[ypekka]

1. There are no screen(s) left of the main screen and all previews are visible.

2. There is a screen (BetterDisplay virtual screen in this case) left of the main screen and only active windows and windows listed in Stage Manager recent windows list are visible.

3. The virtual screen is moved above the main screen and all previews are visible again. The additional screen could also be on left as long as it is not directly beside the main screen but top left or bottom left direction and not overlapping vertically the main screen more than about 50%.

This problem occurs on at least three different machines, that I have access to, with physical or virtual screens.

[lwouis]

Thank you for sharing some visuals.

If I understand correctly, you're saying that some previews are missing when, and only when:

• Stage Manager is enabled
• There is a screen left of the main screen, overlapping vertically at least 50% of the main screen height

And in that case, only the previews from that leftmost screen are missing. Is that correct?

I'm wondering if this could be caused by the pinned issue #1324 which stems from the OS not sharing windows from other Spaces.

Have you checked Displays have separate Spaces in System Settings here?

Thank you

[ypekka]

Correct otherwise but in my example all windows are on main screen (where screenshots are also grabbed) and there are no windows on other screens left or right. I also configure alt-tab to show only windows from the screen where pointer is which was the main screen. I do have separate spaces turned on though.

[ypekka]

I just tested that I can see window previews from all screens, user spaces and also full screen apps even though I have separate spaces enabled if I configure alt-tab to show all spaces and all screens. Of course previews are broken in same way if I have a screen left of the main screen but window titles are still correctly shown even in that case.

[lwouis]

This issue is quite complex, so I'll try rephrasing you, to make sure if I understand correctly.

You're saying that this case exists:

• All windows are on the main screen, and no other screen has a window
• Stage Mananger is ON
• You alt-tab, and while all windows are shown, the ones not present in Stage Manager UI don't have screenshots, as such:
  

Is that correct?

I'm trying to get to a single use-case that demonstrate the issue with minimal amount of complexity.

[ypekka]

Simplest use case to trigger the issue would be:

Configuration:

• Stage Manager is ON
• There is a screen directly left of the main screen
• There are enough windows on the main screen to not fit on Stage Manager's recents list
• It helps to observe the issue if Alt-Tab is configured to show windows only from the screen where the pointer is but it does not affect the issue

Steps to reproduce:

• You are working on the main screen
• You Alt-Tab => your main screen windows that are not either active or fit in recents list have only titles and no previews

It doesn't matter if there are windows on other screens or not.

[lwouis]

I looked into this issue. I think it's unrelated to screen position. I think it's purely related to what fits on Stage Manager.

I did a test with something like 40 Finder windows. When I switch to another app, let's say Chrome, I see all those Finder windows going into Stage Manager. However, Stage Manager only show a stack with 3 windows. The other 37 windows are not visible.

When summoning AltTab, I see the 3 windows from Stage Manager. The others are shown, but with no preview.

This is the way macOS is doing it: when you minimize a window for instance, the actual window is shrunk, and put on the Dock. Same thing with Stage Manager. The actual windows are shrunk or hidden. It seems like Stage Manager doesn't render more than 3 window per app, and the other don't keep their buffer, thus when AltTab asks macOS, it gets no image to display.

Nothing we can do about this. The same way we can't do anything about the thumbnails being skewed and low-resolution when Stage Manager is enabled. In general, Stage Manager breaks AltTab, and there is nothing we can do about it :/