This function is useful for applications that constantly output new information. If value FALSE is returned (that is, no part of the window is physically visible), the application can choose not to redraw, since redrawing is not necessary.

If an application is using WinIsWindowShowing, it must issue the call every time it has new information that needs to be updated. If this is not done, invalid screen content could result. The alternative to this approach for a constantly-updating application that has new information is for it to invalidate its window and redraw within a WinBeginPaint - WinEndPaint sequence.

FALSE is returned if the PM session is not currently visible.