[LV2] lv2_descriptor() considered harmful

Martin lv2list at unknown-error.com
Sun Feb 26 05:02:18 PST 2012

Hi David,

thanks again for the reply :)

> This sounds like a dynmanifest problem, though I suppose you could
> literally write Turtle files to the bundle at discovery.  I never
> considered that.  It's a bit crazy, particularly since such a bundle
> couldn't be installed to the system path.

well, that sounds indeed crazy to me too ;) - I have no Idea how a host 
would magically know of that plugin...

I already had a brief look at dynmanifest but wasn't sure If I really 
need it and if it is worth breaking compatibility to hosts not 
supporting this feature. Also since the manifest in my case is already 
written when the plugin is instanciated I wasn't sure if it's even 
useful to me.

my intended workflow of a user is:

- install binary package containing the .so file (system wide)
- create dsp code using a scripting language and include all input and 
output specifications which go into the manifest later. The amount of 
inputs and outputs is fixed. (at the moment: stereo, 5 controls).

- parse the script in order to create the manifest
- copy manifest + .so (already compiled) and all other needed files into 
.lv2 bundle
- copy this to into ~/.lv2 (so the script's code can still manipulated 
by the user - except of the uri and controls)

after this procedure nothing should be necessary to be compiled. The 
plugin .so file should be able to read its URI from its own bundle 
directory at discovery by looking into its manifest (or an extra file in 
the bundle directory).

I'm not sure if dynmanifest would help here since the amount and 
description of controls remains the same at run time. Maybe I could use 
it to let a user modify the control input's maximum, minimum, etc. (but 
I'd rather do that at a later point)

> I very strongly suggest you *not* release code using some unknown
> discovery mechanism.  There's hardly a point in using a generic plugin
> interface (i.e. LV2) at all, then.

sure, that's also what I had in mind. I hope reading the uri from the 
bundle directory is intended... ;)

> Many people need such a thing, we should just agree on one and put it in
> the core.

I've hardly had experience with lv2 - and also programming in general - 
so please regard my opinion on this URI thing as minor. However I agree 
that we need a feature as you proposed earlier.

- martin

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