Background is bleeding through non-transparent window edges on special workspaces with blur

[ArkadyBuryakov]

Prerequisites:

decoration {
    blur {
        enabled = true
        special = true
    }
}

Also enable gaps on special workspace

Steps to reproduce:

1. Open a window on general workspace
2. Open special workspace
3. Open a non-transparent window (e.g. kitty with background_opacity 1)

Result:
✔️ Window from general workspace is blurred
❌ Background image is bleeding through edges

Kooha-2025-09-19-11-18-53.mp4

Probably this is caused by some optimizations that do not render parts of general workspaces that are under non-transparent windows.

[ItsOhen]

I don't get it. What is the issue here? Gaps are not part of the kitty window.

[ArkadyBuryakov]

Problem is that blur is applied not to a window under the kitty window, but a background image instead. This causes visual artifacts in gaps. You can see them in the video.

[ArkadyBuryakov]

Proposed a fix in this PR: #12027