Signals

[felixroos]

add signal node:

impulse(4)
.signal(() => Math.random()*880+440)
.lag(.1)
.sine()
.out()

here, the callback passed to signal will be executed each time the input gets positive.
In this case, the callback will be called 4 times per second.
The value returned from the callback will be sent to the audio thread to be used as the new value for the signal node.
You can also schedule updates manually, and return nothing / undefined.
The callback gets time (this.playPos) and id (of signal) as arguments.
Like the CC ugen, the Signal ugen can be updated via setControl.
The Signal ugen will send a SIGNAL_TRIGGER whenever its input goes from 0 to positive.

I've already implemented a simple strudel scheduler using signals, which will follow in another PR.
Signals seem useful for general sequencing operations that should not run at audio rate.

It's also comparable to hydra, where you can pass a function to a node to feed values from the main thread (hydra is fixed to 60fps, whereas kabelsalat signals are triggered based on the input)

Limitation 1: on evaluation, the signals of the old graph stop to work atm.
With longer fadeTimes, this gets audible. There should be a way to improve this in the future.
Limitation 2: on evaluation, all signal values reset. It would be smoother if the current value could somehow be passed aloong. This probably only works if the id stays the same.