   TestCooperativeLevel() problem
  So, every time I alt-tab away from my program, all 3D graphics fail to render on the screen (although text drawn with DrawText continues to render).  Everywhere I look for info on this problem, it says that when your app loses focus, the device may be lost, and so you should check every frame for the status of your device with TestCooperativeLevel().My problem is that device->TestCooperativeLevel() always seems to return D3D_OK, even when it pretty clearly should not.  Is there something else that could be my problem, or do I need to do some other trick to get the device to notice it has failed?   
  Is your app running fullscreen or in a window?;  If you're depending on mouse input for view parameters, for example, switching out might give you wrong view values.Check what your app is trying to draw. It may be that you're not drawing correctly. If text continues to be drawn, this is likely not a problem with a lost device.   ;  It WAS me losing the mouse!  Thanks very much!   