Feasability of Mica-like "blur"

[StormDragon-64]

You have mentioned that adding blur would require large changes and multiple render passes, which would slow things down. This makes complete sense. But I was wondering about the feasibility of adding Mica-like or static blur, where you pre-apply a blur to the user's background and then save that as a separate image, and then use that as the background behind an app when it is transparent. Of course, this effect becomes obvious when you have floating windows, but imo it still looks aesthetically better than transparent windows in this case.
Now, I know nothing about the internals of sway or wlroots, so there's a chance I'm suggesting this when there is no easy way to change which background shows behind an application, but my guess is that it would be simpler to implement than realtime blur. And of course, it would definitely perform much better.

[dawsers]

Yes, that would also be possible to implement, and like you said, it would be less demanding on the system. The problem is it is clearly wrong in many situations like the ones you mention, and others, and soon people would complain about it not working correctly in this or that case.

My current stand is I am in no rush to implement blur. I could do it, but I would have to make big modifications to the wlroots renderer. wlroots is going through a transition to make the vulkan renderer the default one. All the new HDR and color space features only work on vulkan, so I am quite certain vulkan will become the default backend very soon, probably with the next version of wlroots and sway. This also means the renderer is not as stable as the gles2 one, and still receives changes frequently. I had to make changes to it when I added shadows, rounded corners, titlebars, etc. but that was easy compared to the architectural modifications needed to render multiple passes for blur. I use the vulkan renderer on my system, and I have had no problems with it, so it is quite mature, but will not be the default one before things settle.

There is also a new wayland protocol, ext-background-effect that will simplify and standardize how things like blur interact with applications. It is starting to get support from applications, but it is quite new, and not everyone uses it. So I wouldn't want to implement something and then realize things need to change completely. wlroots doesn't support it yet.