XComposite input redirection/transformation proposal

[Keith Packard]

On Sun, 2008-02-17 at 03:56 +0100, Dennis Kasprzyk wrote:

> Now how should we handle grabs?

Not to discourage you from trying, but this is one approach I tried a
couple of years ago; grabs turn out to make this so hard that I
abandoned it and threw away the small amount of code I had started to
write.

The server really wants to know *right now* which window an event is
targeted at; it cannot process any more input events or client requests
until it resolves whether the current input event causes a grab to fire.
Then there's the whole synchronous grab adventure. In many cases,
executing X requests would require a sequence of coordinates to be
transformed before the request could be satisfied.

This meant that lots of X requests would need to block waiting for the
redirection client to process a bunch of coordinate transformations.
Things like 'QueryPointer' turned into quite the adventure;
TranslateCoordinates was even more fun. Replay*, and AllowEvents would
require that the *whole* set of queued events be transformed atomically
before the request could be completed.

It may be possible to do all of this, but providing some mechanism for
performing the coordinate transformation entirely within the X server
seems like a far easier, and less invasive, change.

-- 
keith.packard at intel.com
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