fix(xwayland): Properly hide KDE video bridge

[FreddyFunk]

I installed KDE Plasma alongside my COSMIC desktop installation, so I can use KDE when gaming. After logging in to COSMIC after the KDE installation, I ran into #1204. This properly fixes #1204

Without these fixes:

2026-08-31.20-39-56-firefox-hq.Copy.1.webm

With these fixes:

2026-08-31.20-28-33-firefox-hq.webm

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[git-f0x]

Just a note that newer versions of KDE don't use the bridge anymore, afaik (I don't see it on COSMIC on Arch). But this is likely still a correctness improvement for the Xwayland impl (as mentioned in the issue).

[Drakulix]

Thanks, this is an improvement, but I don't think I like how the below layer is implemented here.

First of all, this is very targeted at the video bridge, which we don't officially support in the first place and thus only implements the Below layer. But proper support would also care about the above layer. Imo those should be treated as conceptionally being on the same layer as layer-shell Bottom and Top elements.

Second of all, I am not sure we want to implement the Below hint. Different to layer-shell, these are workspace specific, can be grabbed and the window can request on it's own to be placed below everything or above everything without any user intervention. And thus they suddenly can also not be tiled anymore?

I don't think any of this is good UX. Yes it fixes the Xwayland video bridge, but this gives the same ability to any X11 app and I question that we need to support this mess.

If we want to support it, then this needs to go through @pop-os/ux first and we need to discuss in detail how it shall work.

[Drakulix]

I don't think I like the effective_alpha approach here. It is error prone, as you need to make sure to use it every time any window that is potentially from Xwayland is rendered. Imo this should simply be part of CosmicSurface::push_render_elements. There is no case where we don't want to respect the windows opacity. This is identical to AlphaModifier for wayland windows imo.

[FreddyFunk]

Just a note that newer versions of KDE don't use the bridge anymore, afaik (I don't see it on COSMIC on Arch). But this is likely still a correctness improvement for the Xwayland impl (as mentioned in the issue).

I did a fresh install of the Fedora 44 COSMIC spin, updated everything and then added KDE Plasma and the KDE video bridge was installed 🤷‍♀️

[FreddyFunk]

@Drakulix yeah, that's fair. I converted this pull request to a draft while it goes through @pop-os/ux first