Frosted Glass (Blur) effect

[Drakulix]

Draft for supporting ext-background-effect-v1 in cosmic-comp.

Depends on ongoing smithay work:

• element/damage: Better support effects on framebuffer contents Smithay/smithay#1910
• feat: sub-frames Smithay/smithay#1946

This also introduces a config value (for testing, you need to remove that manually) in XDG_STATE/cosmic-comp/appearance_conf for the blur-strength, but I am pretty sure we want to move this into the CosmicTheme. So this is also partially blocked on support in libcosmic.

This ended up being much more complex than anticipated, due to necessary and quite invasive changes to smithay's public api and damage-tracking.

Additionally this reworks all of the element-collecting code with heavy inspiration of niri-wm/niri#3113. The blur-effect of the main-surface needs to not be affected by drop-shadows, but drop-shadows should still render below the main-surface. Which was easy enough for the floating layout, but when tiling we additionally want to make sure no drop-shadow can extend on-top of another tiled window, so I had to split the element-generation into "lower" and "top" surfaces to order all the drop-shadows in the middle.

This definitely needs wider testing with all the code this touches, but I cannot find any new rendering glitches at this point.

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[git-f0x]

This seems to make the panel, applets and layer shell surfaces (e.g. workspace overview) very sluggish. Is that expected for now?

[Drakulix]

This seems to make the panel, applets and layer shell surfaces (e.g. workspace overview) very sluggish. Is that expected for now?

Should be fixed now with the latest commits.

[ryzendew]

can you explain more about the appearance_conf and how the syntax for blur goes? the details are a littler lacking to test.

[Drakulix]

can you explain more about the appearance_conf and how the syntax for blur goes? the details are a littler lacking to test.

The syntax is blur_strength: 1 with values from 0-14. (Though 0 doesn't actually disable it at the moment.)

The value is 9 by default, so you don't have to set it. If you aren't seeing any blur, the reason is simply, that you aren't running any application supporting the ext-background-effect-v1 protocol, as those are pretty rare at the moment. Our apps also don't make use of this yet.

[Drakulix]

This is now only really blocked figuring out how we want to configure this / make the necessary changes to cosmic-theme.