I have a NSOutlineView and want to draw the cells myself, including a background for the parent/child combinations for the whole width of the View.

I have subclassed NSTextFieldCell to draw the main content including the background shown here:

http://dev.degrees.org.uk/outlineview.jpg

My problem is the OutlineCell that NSOutlineView uses to draw the small triangles and that is responsible for the expanding/collapsing of the rows. Obviously from the screenshot you can see I need to be able to draw the background in these cells to match up with the NSTextFieldCell.

Any ideas how to do this?