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

[David Olofson]

On Tuesday 10 December 2002 08.00, Tim Hockin wrote:
> > It doesn't have to, unless it actually cares. If you save a
> > preset with a "bad" value in some field, the plugin will just fix
> > it when you load the preset.
> >
> > There's just one problem: In what order do you write the controls
> > back to ensure you end up with the exact same result?
>
> The order the plugin presents them to you?

Yes, but requiring that would mean you have to rewrite all controls 
whenever you change one of them, even for automation.


> If there are
> dependencies between controls can we have the plugin author be
> responsible for making their indices reflect it?  Otherwise we can
> add yet another field to controls which says the order in which to
> write presets.  Ick. Serialize/deserialize solves this nicely, btw
> :)

Aaargh! Nooo!!! :-)

Anyway, I think this issue has been resolved rather nicely already. 
We concluded that if a plugin for some reason does not want to 
"accept" certain values, it has to deal with that internally, in a 
concistent way which depends only on the current values of controls 
involved.

It's real simple actually; just have a single function 
fix_bad_values() that you call whenever one of the interdependent 
controls changes. Then it doesn't matter in which order you write the 
controls; the function will always do the same thing.

Oh, and it seems that this applies to 1 plugin in 100 or so - and 
that one is probably just a poor design in the first place. :-)


> > Anyway, if the host *does* keep track of "last value written",
> > supporting the "I'll make that X instead!" event is just a matter
> > of writing X into that "last value written" variable.
>
> Exactly. If a plug doesn't support it, no big deal.  If it does,
> cool.

Yeah, but that turned out to be the easy part... The interface may 
look simple, but it implies quite a bit of hairy situations.

In short, not worth the effort, especially considering that it's just 
an emergency exit for bad plugin designs.


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

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