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<p>The idea is that input ports can never be modified by the plugin.<br>
</p>
<p>If you want your plugin to be able to change its own parameters,
you can already use the patch and parameter APIs together to
achieve this.<br>
It was a bit painful before, but host support for this is
improving.<br>
Qtractor, Carla, mod-host, jalv and synthpod support this. While
Ardour has some level of support but not complete afaik.</p>
<p>Now, if you really want to keep using control ports and have a
way to change parameters, see discussion at
<a class="moz-txt-link-freetext" href="https://github.com/lv2/lv2/pull/42">https://github.com/lv2/lv2/pull/42</a></p>
<p>Rui started a proposal already implemented in Qtractor and his v1
instruments.<br>
I dislike his approach because it requires the plugin to use an
Atom port for notifications, which is overkill for simple plugins
that do not need it for anything else.</p>
<p>I made my own extension which is just a feature with a function,
but it is only a request that the host is allowed to say no to
(this is quite important, as there might be parameter automation
lines for the parameter in question, or being modified by some
external source, or locked by the host for some reason)<br>
See the spec of it
<a class="moz-txt-link-freetext" href="https://github.com/KXStudio/LV2-Extensions/tree/master/kx-control-input-port-change-request.lv2">https://github.com/KXStudio/LV2-Extensions/tree/master/kx-control-input-port-change-request.lv2</a><br>
Currently only implemented in mod-host, but I will add it in Carla
before the next v2.3 release</p>
<p>For surge, the best is very likely to continue the work on the
lv2-parameters target branch. We started some little work, but it
is not finished.</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 20/12/20 10:49, Sven Jaehnichen
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:01e334e7-c7df-fada-a932-0cb9c1ff0b50@jahnichen.de">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<p>Hi,</p>
<p>the old problem: control ports are READ_ONLY in LV2. Me and
other plugin programmers struggle about it. I know it has been
discussed here before and I know the workarounds (like
parameters) and their limitations.</p>
<p>Actually I read in unfa's software chat that the Surge
programmers team are struggling about this problem too:<br>
</p>
<p> </p>
<blockquote type="cite"><span><code class="code-colors inline">We
made this choice because parts of the current LV2 spec and
Surge are incompatible in a couple of ways, most importantly
in the LV2 assumption that plugins never modify their
control input port. Actions like ‘changing parameter types
when an effect changes’ or ‘patch changes’ are not
compatible with this design constraint. As a result, the LV2
- especially in Ardour - unreliably saves and restores
state. The solution - which we are working on - is to use
new LV2 APIs that allow current Surge behavior (and match
what other plugin specs like AU and VST do).</code></span><code></code><br>
</blockquote>
<p><br>
</p>
<p>My request: LV2 UI can call the host to change control port via
the write_function(). I don't see such an option for the DSP
instance. Why? It would be nice to have it. Or are there
restrictions why it's impossible or problematic to implement?</p>
<p>Best wishes<br>
Sven<br>
</p>
<br>
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