ellis@cadillac.siemens.COM (Ellis Cohen) (10/14/87)
WARNING TO APPLICATION WRITERS
EVENTS GENERATED BY XSendEvent
FORCE ON THE THE MOST SIGNIFICANT BIT OF THE EVENT CODE
XSendEvent can be used to send events to a client and these can
masquerade as real X events. XSendEvent is useful for scripts -- as
a way of playing back canned demos. The Siemens RTL Tiled Window
Manager uses XSendEvent in a different way -- it (optionally)
uses XSendEvent to send key presses typed while the cursor is in the
window header on to the client (acting as if the cursor were in the
client's window).
The X server sends the event on to the client, but forces on the most
significant bit of the event code. Unfortunately, many existing clients
are oblivious to this part of the protocol and may work incorrectly
in situations where XSendEvent is used.
For example, the code
XNextEvent( screen->display, &event );
if ( event.type == KeyPress )
...
will not work correctly if the KeyPress was produced by XSendEvent.
If the application wants to work the same regardless of whether the event
was real or not, its code should look like
XNextEvent( screen->display, &event );
event.type &= 0177; /* Mask out XSendEvent indication */
if ( event.type == KeyPress )
...
Those applications using XtDispatchEvent need to do the same thing,
since the version of XtDispatch on the release tape does not mask out
the high order bit. We have had to patch a number of applications in
this way including emacs and xterm.
Ellis Cohen
Siemens RTL Tiled Window Project
(609) 734-6524
ellis.cohen@a.gp.cs.cmu.edu