This also allows to disable the resampler, effectively disabling
varispeed support, for the benefit of adding no additional latency.
By default 2 * 16 samples latency are added, due to port-resampler,
this is not desirable if Ardour is used as mixer only.
Session::route_processors_changed accumulates signals emitted
in realtime and processing is delegated to a dedicated rt-safe
thread. Previously this resulted in any changed to be converted
to a `GeneralChange`, which unconditionally triggered a route-reorder.
Record-arming a track causes a MeterPointChange (meters change to "in"),
and this caused routes to be resorted and a latency-update.
While the former is reasonable (Ardour prefers to process
rec-armed routes first), the latter certainly is not.
Even if we start at time T, if the tempo point before T is ramped, we need to
adjust it's omega value based on the beat time of the following tempo point. If
we don't do this, then using that tempo to compute ::superclock_at() for
subsequent points will be incorrect.
Note: there may be an ordering issue here with Tempo/Meter points. We might
need to pass over all tempo points first, then process meters etc. Something
like that.
libs/ardour/session_state.cc:1500:13: note: in instantiation of
function template specialization 'XMLNode::set_property<unsigned long>'
requested here
libs/pbd/pbd/string_convert.h:151:11: error:
type 'unsigned long' cannot be used prior to '::' because it
has no members
The master needs to be restored first, otherwise setting
the master value with be propagated. Furthermore the
actual value is saved at the time of VCA assignment.
Restoring the vaule needs to scale by the master-reduced value.
changes in tempo can be negative (decelerando/slowing down), and thus so can _omega. We cannot call log() or its
cousins on negative values, so in this scenario use an alternate expression for "t from b" in the tempo.pdf paper
We discovered in the past that the C++ API for GSource/Glib::Source has some fatal and unfixable flaws. Copy similar
code and just use the C API for GSource instead
This is based on code from earlier commits that were later reversed, but we need some mechanism
to ensure that threads have a thread local tempo map ptr set. The big difference is that this
time we do not implement this for all instances of an AbstractUI - implementation is left to
each thread/event loop
