[PATCH 5/5] dxgi: Implement fullscreen window occlusion detection.

[Henri Verbeet]

On Wed, 24 Apr 2019 at 06:29, Zhiyi Zhang <zzhang at codeweavers.com> wrote:
> On 4/24/19 12:51 AM, Henri Verbeet wrote:
> > What is the actual issue with VisibilityNotify?
>
> The problem here is that to implement occlusion detection correctly 100%, we need something like VisibilityNotify events[3] on Linux.
> But for VisibilityNotify events to work reliably, we need to disable compositing. Modern window managers are compositing
> managers for those fancy visual effects, so they are using compositor by default, thus making VisibilityNotify events unreliable and even GTK
> stopped using them[4]. For some window managers, we could disable compositing when entering a full-screen app to get VisibilityNotify events
> working. But for GNOME Shell 3, I didn't find a method to disable its composition. And what's more, disabling compositing on DWM is per monitor
> while current Linux window managers are per screen. So if you disable compositing, you lose all the fancy effects on other monitors as well on Linux.
>
> To test window manager compositing and VisibilityNotify events. You can see this commit[5] for commands to disable compositor.
> Then use `xev` to open a test window and try moving another window over it and see if VisibilityNotify events show up.
>
Ok, so the issue is that we're not getting VisibilityNotify when the
user is running a compositor. (For reference, VisibilityNotify events
do work here on fvwm, but I can also confirm that running e.g.
xcompmgr or compton effectively disables them.)

In any case, it looks like Vincent has provided a workable alternative
suggestion in a parallel private thread. Ideally that discussion would
have happened here on the public mailing list, but oh well.