How Do I Have Transparent NSTableView/NSOutlineView Floating Group Rows in Big Sur

Hello

My application uses NSOutlineViews with a floating group row as the title. In previous versions of macOS I have had a semi-transparent background to my heading, so scrolling rows can be seen underneath.

In Big Sur there is a solid background to my floating row, and a thin border drawn on the bottom edge. I can see no way of stopping this background being rendered!

I have a custom NSOutlineView with all drawing overridden:

Code Block
override func draw(_ dirtyRect: NSRect) {}


I have a custom NSTableRowView with the same override.

If I set the NSTableRowView that is floating to hidden, the background and border are still visible.

The parent view of the floating row (a subview of NSScrollView) has the same dimensions as the whole scroll view, so I suspect the background is being drawn into this view, but by what!?

Any ideas welcome please.


How Do I Have Transparent NSTableView/NSOutlineView Floating Group Rows in Big Sur
 
 
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