You now need to bring your own buffer instead of the smoother having a
built in vector you would need to pre-allocate. This makes the API
simpler, and also much more flexible when doing polyphonic modulation.
In addition, the new API is much more efficient when there is no
smoothing going on anymore.
Only a couple of these functions would be needed during initialization.
In the next couple commits ProcessContext will get a way to access
auxiliary IO, so this really had to be separated.
The missing parts are allocating buffers for these busses, copying data
to those buffers, and adding methods to the ProcessContext to interact
with these inputs and outputs.
This required rewriting the way events and parameter changes are handled
for VST3 by putting them all in a single sorted array, because we can
now no longer read directly from the host's events list because we also
need to mix these new generated MIDI CC events in with it.
This is a breaking change requiring a small change to plugin
implementations.
The reason why `Pin<&dyn Params>` was used was more as a hint to
indicate that the object must last for the plugin's lifetime, but `Pin`
doesn't enforce that. It also makes the APIs a lot more awkward.
Requiring the use of `Arc` fixes the following problems:
- When storing the params object in the wrapper, the `ParamPtr`s are
guaranteed to be stable.
- This makes it possible to access the `Params` object without acquiring
a lock on the plugin, this is very important for implementing
plugin-side preset management.
- It enforces immutability on the `Params` object.
- And of course the API is much nicer without a bunch of unsafe code to
work around Pin's limitations.
This now is a single vector with all of the information in the correct
order instead of the hashmaps and a vector. This avoids deduplication,
and it especially makes manual `Params` implementations a lot more
convenient since you can't mess up with mismatching IDs between the
methods.
To accommodate exactly this, the persistent fields methods also have a
default implementation and the trait has been marked as `unsafe` since
it's the programmer's responsibility to make sure these `ParamPtr`s will
remain valid.
