wayland/background-effect: add ext-background-effect-v1 (blur region)

[bbedward]

core/region: add radius to create rounded regions

Adds BackgroundEffect that allows setting blur region on layer shell surfaces, additionally adds a radius option to Region similar to the vicinae pattern for making approximate rounded regions.

To test on a supported compositor: qs -p src/wayland/background_effect/test/manual/background_effect.qml

Usage is as:

BackgroundEffect.blurRegion: Region {
        item: root.contentItem
}

[YaLTeR]

Seems the region passed to the protocol also needs to be offset by the Qt CSD, if any:

Better visibility of the region:

[outfoxxed]

For consistency with existing interfaces, this should probably be an attached object. See HyprlandWindow for an example.

Do we have any options for blur opacity exposed?

[bbedward]

For consistency with existing interfaces, this should probably be an attached object. See HyprlandWindow for an example.

Changed it to an attached object, the only downside I guess is my thought was getting a BackgroundEffect.active to tell if the compositor had applied it/supported it

Do we have any options for blur opacity exposed?

That's not exposed by the protocol, its just blurRegion and capabilities { blur } pretty much. The effect parameters themselves would be set elsewhere, like niri's compositor config in this case.

[outfoxxed]

Rather disappointed in the protocol itself but the implementation is mostly there.

[outfoxxed]

Good overall

[outfoxxed]

Added missing controls to the tester and noticed the corner radius is entirely unclamped at this point so it will break if you take it out of bounds. It should clamp at the point where its bounded by the size of the rect or space used by other corners

[bbedward]

Added missing controls to the tester and noticed the corner radius is entirely unclamped at this point so it will break if you take it out of bounds. It should clamp at the point where its bounded by the size of the rect or space used by other corners

Added the clamping to region

[outfoxxed]

It seems like we're still getting intersections from circles in opposite corners

[bbedward]

It seems like we're still getting intersections from circles in opposite corners

I changed the approach again, to cut the corners out of the rectangle. All the scenarios I tried in the tester seem to work for me

[outfoxxed]

lgtm in testing

[outfoxxed]

Modified to use ext-bg-effect from w-p and split commits. Will merge once CI passes.