Created attachment 111049 [details]
Expected: corners are round even without borders

The border radius would allow to round window corners. (similar to the CSS border-radius property, https://www.w3schools.com/cssref/css3_pr_border-radius.asp)

At a given moment, in order to round window corners, a decoration theme should add borders and round corners by itself. That approach has a big disadvantage, it doesn't work with "borderless" windows. Maybe, KWin should handle border radius property...

It would be great to have the following class method in KDecoration2::Decoration:

```cpp
void setBorderRadius(int radius);
```

This method would apply a given border radius to all corners.


Possible implementation: do clipping when rendering windows?