Created attachment 172515 [details]
Old behavior, showing background color in blur region without being over background.

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SUMMARY
In the past, the blur used to sample an area outside the current window to prevent temporal artifacts.

At some point this was changed and now the blur only samples areas that are in the window region.

This makes the blur look bad, like it does on Windows ( because they do the same thing, only sampling what is under the actual window region )

I'm not sure why this was changed, or what led to it, but it would be awesome if we could get the old behavior back.

I have attached 2 images showing the difference.

STEPS TO REPRODUCE
The setup is this, a terminal with a transparent BG on top of a non-transparent VSCode window. The terminal is placed overlapping to the left edge of the VSCode window, and in the old method you can see the color of the background bleeding into the terminal ( as it is transitioning from Window -> Background ). But in the new image you can see no such transition, it's only after you move the terminal past the edge of the VSCode window that you will start to see the background colors in the blur. 

OBSERVED RESULT
Background color does not bleed into terminal blur region until window is past the edge of the non-transparent VSCode.

EXPECTED RESULT
Background color to show in the blur before reaching the edge or beyond the edge of the non-transparent VSCode window.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 6.1.3
KDE Plasma Version: 6.1.3
KDE Frameworks Version: 6.4.0
Qt Version: 6.7.2

ADDITIONAL INFORMATION