usage of snd_seq_set_client_event_filter

usage of snd_seq_set_client_event_filter

[Kaspar Bumke]

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Hi all,

I was trying to use snd_seq_set_client_event_filter in my application but I
can't seem to get it to work correctly.

I have attached a small test program which can be compiled with "g++ -o
test test.cpp -lasound".  My alsa-lib is at 1.0.25. It should simple print
the note number for any noteOn events.

I was under the impression that the way I have used it only noteOn events
would get through but it seems that only the first noteOn event I send it
gets through. I have been sending events using VMPK.

If I remove snd_seq_set_client_event_filter everything seems to work
(except the events aren't filtered of course).

What am I doing wrong?

All the Best,

Kaspar

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#include <alsa/asoundlib.h>
#include <unistd.h>
#include <iostream>
using namespace std;

snd_seq_t * handle;

int main() 
{
	snd_seq_open(&handle, "default", SND_SEQ_OPEN_INPUT, 0);
	snd_seq_set_client_name(handle, "test");

	//snd_seq_set_client_event_filter(handle, SND_SEQ_EVENT_NOTEON);

	snd_seq_create_simple_port(handle, "in", SND_SEQ_PORT_CAP_WRITE | SND_SEQ_PORT_CAP_SUBS_WRITE, SND_SEQ_PORT_TYPE_APPLICATION); 
	while (1) {
		//sleep(1);
		snd_seq_event_t * event;
		if(snd_seq_event_input(handle, &event) >= 0)
			cout << (int)(*event).data.note.note << endl;
	}

}

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Re: usage of snd_seq_set_client_event_filter

[Kaspar Bumke]

Sorry, in test.cpp, the line with snd_seq_set_client_event_filter should be
uncommented of course.

Re: usage of snd_seq_set_client_event_filter

[Clemens Ladisch]

Kaspar Bumke wrote:
> I was trying to use snd_seq_set_client_event_filter in my application but I
> can't seem to get it to work correctly.
>
> I have attached a small test program which can be compiled with "g++ -o
> test test.cpp -lasound".  My alsa-lib is at 1.0.25. It should simple print
> the note number for any noteOn events.
>
> I was under the impression that the way I have used it only noteOn events
> would get through but it seems that only the first noteOn event I send it
> gets through. I have been sending events using VMPK.

Any filtered-out events gets rejected with an error, which gets reported
back to the sending application.  If that application does nothing to
handle the error, all further attempts to send events will get the same
error because the event being rejected is still in the output buffer.

This behaviour makes event filters pretty much useless.
Just ignore any events you don't want.


Regards,
Clemens

Re: usage of snd_seq_set_client_event_filter

[Kaspar Bumke]

>
> This behaviour makes event filters pretty much useless.
> Just ignore any events you don't want.


Ok, will do. Thanks for the answer!