[gmpi] Re: Decision time: 8.1

Paul said: 
this raises a deeper question that should perhaps wait: what happens
if the plugin author wants to offer a choice of:

   a) connect this port to a signal to control my output
   b) use this knob to control my output

this is not hard to imagine for anyone who has ever used a modular
synth. it throws a wrench in the works, though, because connections
are between ports, not parameters. or are they? etc.


True. But it may be possible to resolve these two models into a single mechanism, if that's what you want to do. So this doesn't necessarily have to be an either/or choice at this stage. The rest of this email shows one way it could be done, perhaps -- so if not interested, stop reading now.

In other words, forego the usual plug::setParameter() and instead handle setParameter() as an abstraction of event generation in the graph object, not as a direct plug-in method. So all plugs would have to implement a Parameters port (simple if always at the same port index, though still doable even if it moves around).

So instead of doing this:

thePlug->setParameter( paramIndex, paramValue )

you do this:

theGraph->setParameter( thePlug, paramIndex, paramValue )


which inside the GMPI framework would be defined as something like:

result gmpiGraph::setParameter( gmpiPlug& thePlug, short paramIndex, BYTE& paramValue ) {

#define kPARAMETER_PORT 0 // Known port index that all plugs support for parameter setting
#define kEXECUTE_NOW -1 // Token for event time parameter meaning execute event immediately

sendEventToPlug( thePlug, kPARAMETER_PORT, kEXECUTE_NOW, makeParamEventData( paramIndex, paramValue ) )
}

This would stuff the generated event at the top of the plug's parameter event queue, where it'd be executed at the top of the next plug::process() call. (There would need to be a known queue ordering rule in case a plug had any parameter setting order dependencies.)

As a side-effect, this approach would time-align the parameter setting processing with all the other incoming event processing, which might help simplify things for some plug types.

Again, this is all only if you want to have a single mechanism. Also not applicable if you feel the need to be able to wiggle the parameters in between process() calls for some reason...

-- Chris G.

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