This makes sound beacons green when playing at
full volume, yellow when playing at a lower volume
and red when they are muted (aka, in another parcel
that you can't hear the sounds of).
Originally this was a debug patch as muted sound
sources used to be implemented by setting the volume
to zero, which happens to use like three times more
CPU: so, having a lot of muted sound source caused
the audio thread to never release a mutex anymore
(cause it was never idle anymore), causing the main
loop to hang, waiting on that mutex - dropping the
FPS drastically. Hence it was necessary to see which
sound sources were muted for debugging purposes.
(Since VWR-14914, muted source source are not played
at all anymore, so they do not take extra CPU).
It's still fun to see this extra information though,
now the patch exists anyway.
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