Just noticed that using the ALLEGRO_FULLSCREEN_WINDOW flag just causes a regular window to be created under Mac OS X. al_toggle_display_flag(ALLEGRO_FULLSCREEN_WINDOW) returns false, suggesting that it is not supported.

If it is not supported it might be a good idea to mention it in the manual. When I create a display with the ALLEGRO_FULLSCREEN_WINDOW flag I can't tell if the created display is actually fullscreen or just a regular window.

Perhaps al_create_display() should fail if that flag is set and it is not supported. That way I can at least fall back to using a regular fullscreen mode.

10.6.7

I think there's a compile-time check for the Mac OS X deployment target (whatever the name of that define is) for whether it's possible to use or not (it's not available on OS X < 10.6.0, I think). If it's compiled for use with an earlier version, then it will fail to create a fullscreen window.
A proper solution is to do the version check at runtime.

@TC: check the compatibility version number that you set when you compiled Allegro.
Yes, it probably should fail gracefully instead of quietly - however, I'm not sure what happens on other platforms in this case. Would need to double check there.

For it to work it will have to be a run time check in Allegro, and a fallback for < OSX 10.6.

That would be good, but I was not even thinking of that. I was thinking of using a regular fullscreen display when fs window isn't available. Is there any practical difference though, assuming someone rigged Allegro to pop in and out of fullscreen mode with the toggle? I know on OSX even fullscreen window behaves worse than fullscreen on other platforms, with Command-Tab and virtually ever way to get out of fullscreen mode not working. I played with that a while back, as there are some options there that supposedly allow command tab etc, but enabling them didn't seem to work (probably my mistake.)