detect menus/tooltips/etc blocking clear view of window

Is there any way of detecting if a window is somewhat obscured by eg tooltips, menus, or other popups which it has opened. I can't find anything relevant in the forums, and would like a more elegant/faster solution than doing a pixelsearch for colours (which would not always work anyway due to lack of distinctive colours sometimes.
I have an OCR function I've written, which monitors in the background and updates other windows, but it intermittently gets caught out by these popups.
Thanks
David