This function retrieves the dimensions of the tightest bounding rectangle that can be drawn around the current visible area on the device. The visible area is defined by the current clipping region as well as any overlapping windows.
The return value specifies the clipping box's complexity.
NULLREGION indicates that the region is empty.
SIMPLEREGION indicates that the region is a single rectangle.
COMPLEXREGION indicates that the region is more than one rectangle.
ERROR indicates that an error occurred.
To get extended error information, call GetLastError.