Event Control Miscellany for an Input Redirection Client

[Keith Packard]

On Mon, 2006-01-23 at 12:05 -0800, Deron Johnson wrote:

> So we need to provide input redirection clients with a way of
> associating additional information with each event. One possibility
> is to add additional client-defined data fields to X events. But this
> would be very invasive to the server and prohibitive to implement.

We cannot change the wire encoding of events

> A better method is for the redirection client to store the information
> in its own address space and include an opaque reference to the data
> in an otherwise unused field of each event. In my implementation, I
> chose to place this in the sequence number field. However, this forced
> me to skip the normal setting of the event's sequence number when
> writing to this client. Perhaps using the subwindow field might work
> better. Is there another field in the event you would recommend for this
> purpose.

We cannot use the sequence number as the protocol binding libraries
(Xcb, Xlib) use these to track X server execution of requests.

I will not like any suggestions that involve changing the core data on
the wire; these are extensions, after all. Sending additional events is
more than possible, and would provide a less scary mechanism.

> In my mind the question is not whether we need such a feature, the
> question is what is the best way to implement such a feature.

No doubt. That's why I want to see several different implementations
before we even start thinking about what might be the best standard one.
What we've got now isn't sufficient, but we must take some care to
ensure that we don't choose something that we will regret in the
future. 

-- 
keith.packard at intel.com
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