API question plugin->host requests

[dbadb]

Greetings clappers,

I'm developing a CLAP host that hosts multiple plugins and am finding an awkward corner of Clap's plugin-to-host API.

The problem:

//host.h
request_callback(const clap_host *);
request_process(const clap_host *);
request_restart(const clap_host *);
// ext/gui.h (host)
request_resize(const clap_host_t *, uint32_t , uint32_t );
request_show(const clap_host_t *);
request_hide(const clap_host_t *);

These methods are invoked from a plugin to request a service from the host. The clap_host struct includes a host_data field which I've been using (following the clap-host example) to stash a pointer to the C++ clap host instance.

The awkwardness is that these requests don't include any plugin-specific context. Ie: the source of the request. The only solution I see is to pass a plugin-instance-specific clap_host with a different host_data for each instance. Obviously doable, but it would seem nicer if these three callbacks also included the clap_plugin * of the originator.

Any comments or thoughts are welcome! Am I missing something?

Thanks!
Dana

[defiantnerd]

You will need to create an object instance for every hosted plugin. This will also contain a pointer back to the plugin instance.
In the clap-wrapper I've introduced an IHost interface and derived the actual wrapping object from it. The pointer to this interface is being provided as clap_host_t*.

https://github.com/free-audio/clap-wrapper/blob/f14d5b24806f1da080d1534199d2668ebd2f5e43/src/wrapasvst3.h#L87

This way I can always find the way back to the plugin and I also know which instance is being addressed.

You will have no success with pointing clap_host_t to the same object for all plugin instances, it is individual for each plugin.

[dbadb]

Indeed - that is the flavor of the course I am taking. That said, I'm curious if the simple API enhancement proposed above would also address your scenarios?

Thanks for taking the time to comment.

[defiantnerd]

I don't think so - but it would introduce the possibility of using a non-matching clap_host_t*and clap_plugin_t*.
And since it actually just two pointers in a struct you have to maintain, this is something you can burden the host with.

Additionally, you will have to maintain some object for each plugin instance anyway, so just use that - it will contain the clap_plugin_t*, I guess.