[LAD] Portable user interfaces for LV2 plugins

David Robillard d at drobilla.net
Fri Mar 4 19:51:56 UTC 2011

On Fri, 2011-03-04 at 15:24 +0100, Olivier Guilyardi wrote:
> On 03/04/2011 01:53 PM, Stefano D'Angelo wrote:
> > Hence, in this case, I think we should exploit the
> > extensibility/decentralization of LV2: those who, like me, care about
> > "control rate" visualization hints may want to help on web UIs, for
> > example, the others might do the same with native GL.
> > 
> > The only thing that we all need to ensure is that things work well
> > together, whatever the host/plugin author choice is, also trying to
> > make the whole thing as painless as it can be for everybody.
> > 
> > Side note: this is yet another case where we could proceed to some
> > structured effort coordination at this point, but my feeling is that
> > this won't happen and the discussion will lead nowhere in the end.
> There is one thing which stays on my mind.
> I am familiar with developing JACK clients, not plugins. However, there has been
> quite a few discussions in the past where JACK was advocated as a way to create
> modules, DSP units dedicated to a specific task. In other terms: some kind of
> plugins.
> And what is absolutely nice about this is how it is non-intrusive. When working
> on a JACK client, there are only audio input and output ports, a thin transport
> layer, done. From these primitives, upon this bare but solid ground, a developer
> creativity enjoys a lot of freedom.
> However, there's been this critical and long-lasting session handling problem.
> Fortunately, this problem doesn't occur for LADSPA and LV2 plugins, since saving
> and restoring state is performed by the host.
> But, with this UI/engine separation, whenever a developer comes out with an
> innovative idea that he really likes, he's very likely to hit a wall because of
> a specific LV2 technical constraint. And at the same time it takes an incredible
> (if only possible) coordination effort to maintain LV2 to fulfill and
> *anticipate* all needs.
> But LV2 is extensible. So what I think is that in addition to the extensions
> which imply UI/engine separation (and I understand that it's important in many
> cases), there should be a DoWhatTheFuckYouWantInYourPlugin extension ;)
> With such plugins, restoring/saving state would rely on passing a blob in
> addition to restoring/saving the control ports values. There would be no such
> thing as UI/engine separation. The plugin would be self contained. And hopefully
> it would integrate nicely with other extensions such as midi.
> I think that this extension, since it would only imply simple but powerful
> primitives, would give a lot of freedom to developers who want that, and at the
> same time be rather easy to maintain.

You are mish-mashing way too many ideas into a big messy ball here for
me to address individually.

However, there is an extension a UI can use to get a pointer to a plugin
instance, which is mostly what you are talking about:


I do not recommend its use for any situation except where it is
absolutely necessary. Its role is either:

1) Temporary kludge used for necessary plugin <=> UI communication

2) A way to get direct access to waveform data for visualisation or
whatever, with graceful degradation where this is not possible

Use 1 is a big red flag that says something is missing and/or broken.
Use 2 is all good.


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