Client display configuration notification

[Alan Griffiths]

On 30/09/15 05:04, Christopher James Halse Rogers wrote:
> Forked from review¹.
>
> I think we're currently handling display configuration events
> incorrectly, or at least in a way that will be surprising to clients.

I totally agree that the existing behaviour is "surprising"; what isn't
clear to me either is what behaviour would be "unsurprising".

I think the problems arise because we conflate three distinct
configurations:

/1/ the "base configuration" as set by the server;
/2/ the "session configuration" as set by the client itself; and,
/3/ and the "current configuration" as set by the active session.

We do make a distinction between "hardware" and "user" options, but that
is simplistic.

I think we should allow the client to query each of the above (unless
/3/ is a security concern?). We also need better tracking of consistency
and differences between the base configuration and the session
configuration. (E.g. currently the session configuration "locks in" the
original values from the base configuration when not set by a client
that "doesn't care", it may be better to only hold the values explicitly
set.)