[linux-audio-dev] Plugin APIs (again)

[David Olofson]

On Sunday 08 December 2002 03.27, John Lazzaro wrote:
> > David Olofson <david at olofson.net> writes:
> >
> > Yes - but we're not talking about MIDI here. We *may* require
> > that events are never lost, and even that it's not legal to send
> > two identical events in line to an event port, unless you really
> > mean something else than to set a controller to the same value
> > twice.
>
> Think ahead about how these sorts of requirements will be enforced:
> will they be a "law of nature" (code checks to see if an app broke
> the law, and takes action, like nature takes action when you try
> to change the current flowing through an inductor :-), or will
> it be unchecked by code? If its the latter, you can get into
> this mode where everyone has extra checking and work-around code,
> to handle impolite API users who aren't obeying the requirements.

Well, I wasn't seriously suggesting that we have that kind of silly 
rules. Still, they would not be totally unreasonable, given that you 
can never have two event sources manipulate the same control in a 
useful way; it would just result in the value jumping around. So, who 
would send the same value twice?

If someone frequently tries to set a control to the value it already 
is set to, that's bad manners.

If a plugin actually starts recalculating filter coefficients and 
stuff as a result of receiving such a control event, that could alse 
be considered bad manners - BUT, avoiding it would mean an extra 
conditional. Why have a conditional to avoid doing something 
relatively harmless, that can only happen as a result of someone else 
being nasty?

That said, if hosts want to filter event streams from poorly written 
event generators, fine - but IMHO, it's a waste of resources, 
shouldn't be needed at all, and can only prevents something that's 
relatively harmless.


Anyway, there might be cases where we can use "trigger" controls, 
where the value is an argument, and the plugin is supposed to 
actually *do* something as a response, every time, regardless of the 
value of the argument.

If we want those, they should be explicitly marked as special - just 
like non-RT events. Or just like the few MIDI CCs that filters may 
not remove. The only difference is that we don't have a fixed set of 
controls with implicit rules, but use use some hints and flags 
instead.


//David Olofson - Programmer, Composer, Open Source Advocate

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