Thanks for fetching that, Tim. The Requirements say:
" 4.21. The Parameter Pre-Processor Model
...a carefully designed way of exposing parameter interactions to the host.
1. Linked parameters
Two parameters, LEFT and RIGHT, are independant of each other,
unless a third parameter, LINKED, is set to true. When LINKED is
true, LEFT and RIGHT are joined at the same value, and move in lock
step. When LINKED is set to false, LEFT and RIGHT can be changed
independantly. All UIs must reflect this linkage.
...
To conceptually handle these issues the idea of the "parameter
actor" or "event pre-processor" was established. The final
implementation is up to the spec and implementation teams, but the
idea is simple. Plugins can optionally expose parameter event
pre-processor methods. These methods encapsulate the logic of
inter-parameter dependencies. Event senders call these methods
synchronously, and are immediately alerted to things such as linked
or clipped parameters."
This seems to be saying that if there is parameter linkage, the actor
tells the host that about all dependent parameter changes. But
that's exactly what Mike says setParameterAutomated(), which he
really wants to avoid, does. If multiple parameters are linked
together, there will be have to be multiple calls per event.
So, I know there must be a difference, else Mike would not have OK'd
actors... but what is it? Is it just about execution time and
threading? These texts don't say.
-- Chris G.
Tim said:
... I quote Mike Berry:
In VST, which Premiere supports, there is a method called setParameterAutomated, which a plugin calls to tell the host that a parameter has changed. Setting aside the rather painful syntax issues, we have seen this method get called in several situations: ... 2.) Parameter linkages, where we call setParameter on one parameter and we get back a setParameterAutomated call for another parameter. ... 2 has caused innumerable headaches for us. Because parameter changes are often undoable, we cannot offer single parameter undo, because multiple parameters may change. Non-uniform linkages have also been a problem. Take 2 parameters, A and B. When you change A it changes B, but when you change B, it does not change A. Now imagine automation recorded for A, then B. When you play back with automation, a little war occurs between the recorded automation for B and the implied values due to the linkage to A.
So the primary tenet was that it was awkward (at best) to get multiple
setParameterAutomated responses for one event. ...
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