VSelectEvents - selects the event types for 3DVIEWNIX windows.
  VSelectEvents(win, event_mask)
  Window win;
  unsigned long event_mask;
  VSelectEvents selects the event types to be sent to a specified window
in 3DVIEWNIX. If the window ID is not valid, VSelectEvents returns 6.
The bits of the event mask are defined in  and they are listed
        ButtonPressMask         NoEventMask
        ButtonReleaseMask       KeyPressMask
        EnterWindowMask         KeyReleaseMask
        LeaveWindowMask         ExposureMask
        PointerMotionMask       VisibilityChangeMask
        PointerMotionHintMask   StructureNotifyMask
        Button1MotionMask       ResizeRedirectMask
        Button2MotionMask       SubstructureNotifyMask
        Button3MotionMask       SubstructureRedirectMask
        Button4MotionMask       FocusChangeMask
        Button5MotionMask       PropertyChangeMask
        ButtonMotionMask        ColormapChangeMask
        KeymapStateMask         OwnerGrabButtonMask
A call on get_event overrides any previous call on get_event for the same
window from the same client but not for other clients. Multiple clients
can select input on the same window if the event_mask passed are disjoint.
When an event is generated it will be reported to all interested clients.
However only one client at a time can select for each of
SubstructureRedirectMask, ResizeRedirectMask, and ButtonPressMask. If a
client attempts to select on one of the three event_masks and some other 
client has already selected it on the same window, the X server generates a
BadAccess error.
Return Value
  0 - work successfully.
  3 - write error.
  4 - file open error.
  win - specifies the ID of the window interested in the input events.
  event_mask - specifies the event mask. This  mask is the bitwise OR of one
        or more of the valid event mask bits.
Side Effects
  If the window ID is invalid, VSelectEvents returns 6.
Entry Conditions
  VCreateWindows must be called first.
Related Functions