ObjectProxy

An ObjectProxy is used to mirror a specific object in a remote tree. It contains the same type signature, information and value. For example, if you have a remote tree synth with some “cutoff” parameter (url = osc://"funky synth"/osc1/cutoff), you will interact locally with the remote synth by reading/modifying the ObjectProxy.

How you design your proxy object in order to interact with it is up to you, this is why ObjectProxies have to be subclassed, usually as some kind of Widget (slider, button, etc). A sub-class of ProxyFactory is responsible for instantiating the right Widget given a remote object’s type signature.

An ObjectProxy keeps a cached value of the remote object’s value. When it receives a local call (through the trigger method), it should return the cached value or update the remote value.

When a local object calls an ObjectProxy, it will always receive the old value as reply since the update operation is asynchronous. Of course, since this is just a proxy, no notification is sent from this end.

When you want to change the value of a remote object, you “do something on the object proxy” (turn a button, move a slider, say “hi”) and this action should call set_value on the proxy. It is the ObjectProxy’s responsibility to forward the change to the remote object it is mirroring.

[slider] --- set_value ---> [remote]/osc1/cutoff 45.0

When you or someone else changes the value of an object, the object sends notifications (see Command). These are routed to the ObjectProxy by RootProxy. When such a notification arrives, it updates the cached value and triggers a value_changed call on the ObjectProxy.

[remote]/osc1/cutoff 45.0 ---> value_changed ---> [slider update]

As you can see, all these updates are made asynchronously (first send a query to change, then receive a “changed” notification). This requires special attention when building the widgets in order to give users a proper feedback on the success or failure of an operation.

Example of a good slider design for async operations.

In the slider shown here, the idea is that the user moves the “ghost” slider freely (this slider is connected to set_value in the ObjectProxy).

The “current value” slider is only changed by the notifications to value_changed. This means that the user “feels” the latency and knows exactly what is happening.