On macOS, SDL Window "flashes" when switching between apps on Mission Control

[philippemnoel]

This is an issue that has been quite bothersome for our engineers and users of our product built on SDL. Here is how to reproduce:

macOS only:

1. Open up an SDL application, we've tested our app and the "Hello, World" SDL basic demo also reproduces the behavior.

2. Open up other applications

3. Focus some non-SDL application, say VS Code.

4. Go to Mission Control view (start with your fingers pinched together in the center of the trackpad, and expand outwards to bring the pan-out view of all the applications on your macOS desktop)

5. Click on the SDL application window. It will either:

   • Flash very quickly the previous application you had focused (here VS Code in this example) and then display the SDL application
   • or it will flash the previous application you had focused, and not focus the SDL application (here I would still be shown VS Code). If this happens, I have to do the whole process again and the second time it will correctly focus the SDL application

This should be easy to reproduce (it is almost 100% reproducible for me when following these instructions).

I am on M1 MacBook Pro Mid-2020 w/ macOS Monterey, but we've confirmed this is reproducible on much older macOS hardware and older macOS versions as well (all the way down to Sierra and 2012 MacBooks).

This sounds to me like probably a short fix. If that's the case, would love to know the solution so we can manually patch SDL on our end and not have to wait until the next release.

Thanks all, as always big supporters of SDL over at @whisthq!

[icculus]

I can see this happen on an M1 Mac Mini on Monterey 12.5.

Sometimes the issue doesn't appear to happen for several attempts in a row, and extremely rarely, the window fails to come to the foreground at all until you click around in a way that raises the window (like click its icon in the dock, etc), even though the SDL app itself was named in the menu bar after the window didn't rise...this makes we wonder if this is waiting for one more round of event queue pumping after reaching the foreground before the SDL window realizes it was supposed to become the key window and does something to correct for that. That would explain what looks like a one-frame blip, and if this is some sort of race condition, explain why sometimes the window doesn't rise at all.

Adding @slime73 to the thread in case this has a super-obvious fix, before I dive in myself.

[icculus]

I still have no idea on this. Maybe we should ping Apple about it?

[slouken]

That sounds like a good idea.

[icculus]

Bumping this to 2.26 to wait for the cavalry from Apple to arrive. :)