HImHideOverlappedText is a class for "hidden text" mode. The idea is to have text obscure other text but not geometry. The requirement that it not obscure other geometry precludes a simple rectangle inserted behind the text, and pushes us into this more sophisticated mechanism.
The first step is that we set an IM callback to intercept all text drawing and store all such calls into a linked list during the normal update. At the end of the update, we z-sort everything and insert the text calls into a quad tree to resolve what text should be drawn with as few comparisons as possible.
This class is a filter that can be turned of and on per driver segment to use call FilterOn and FilterOff from a open driver segment