[PATCH] wayland: Add wl_keyboard:keys_update()

[Bill Spitzak]

Martin Minarik wrote:

> * The client are perhaps more interested in knowing which keys changed,
>   not what is the actual state. Delivering state is less flexible because
>   it requires the client to keep track of state, if it wants to know what
>   changed. But the compositor knows what changed. Client would have to compute
>   this again.

I find the above explanation extremely hard to believe.

In every ui code I have ever worked on the only thing it is interested 
in is "are any buttons held down". I can assure you it is many times 
easier to reliably implement this from an array of what buttons are down.

Also this design requires both the client and compositor to remember the 
previous state. Generating the state change from a state array only 
requires the client to remember the previous state, saving one copy. 
Also avoiding extremely nasty bugs when the compositor and client get 
out of sync!