Merge lp://qastaging/~ywwg/mixxx/features_xwax2 into lp://qastaging/mixxx/1.10

Looking good Owen -- I think this is fine to go in 1.10. I'm going on your say-so that it works since I can't test it myself, so this is just a review of the code assuming it all works :P

enginevinylsoundemu.cpp

* Just to make sure fabs(curRate) is not repeated over and over, could you assign it to a temporary variable once per loop?

* Using rand() in the callback isn't ok because technically it can block if the system has run out of entropy (at least if it's reading from /dev/random). Even if it doesn't block, random number generation aint cheap. Can you pre-generate a large buffer of random numbers in the constructor and just use that (with a class-level stored index into the buffer so you aren't adding the same section each time).

enginebuffer.cpp

* Duration is read from metadata and shouldn't be considered accurate. Also I don't think we should correct it if it's wrong from the engine. Do you rely on duration anywhere from within VC? Can we remove this line?

vinylcontrolsignalwidget.cpp

* There's a constant in vinylcontrol.h MIXXX_VINYL_SCOPE_SIZE that seems to be this number. Can you use that instead?

wspinny.cpp

* in updateVinylControlEnabled() there is some non-ndeck code -- I know VC itself is 2-deck centric, but could you instead add a VinylControlManager::getVinylControlProxyForChannel(QString) method that returns either the proxy or NULL? That way WSpinny doesn't need an update when we eventually n-deck vinyl control.

Just a couple of comments as I work on this:

> enginebuffer.cpp
>
> * Duration is read from metadata and shouldn't be considered accurate. Also I
> don't think we should correct it if it's wrong from the engine. Do you rely on
> duration anywhere from within VC? Can we remove this line?

Vinyl control needs an exact duration (sample-accurate) to calculate position and drift, and the UI timers (time remaining / track duration) also need better precision (there's a bug in launchpad for this). What is the point of the duration member if it's several seconds off? Why not fix it? Otherwise I need to add a new object called "exact_duration" or "calculated_duration" or something.

>
> vinylcontrolsignalwidget.cpp
>
> * There's a constant in vinylcontrol.h MIXXX_VINYL_SCOPE_SIZE that seems to be
> this number. Can you use that instead?

the scope size is the size of the bitmap created by xwax. This bitmap can then be scaled to whatever size the scope widget actually is. I'll set it to default to the scope size, but they don't need to be the same.

This branch is ready for reevaluation.

Looks good to me. Merge away!