Hi,

if the input and output signals have the same channel count, they will alias each other, just like in regular single-channel objects. In that case, your code may accidentally overwrite parts of the input before it is read. You first need to copy the whole input signal to a temporary buffer (probably allocated in your object) and then copy the corresponding channels to the output signal.

ps. While we're at it, I don't get why we have both sp[0]->s_length and sp[0]->s_n, aren't both the same?

Christof

Hi, I'm creating new fun objects that are tools to deal with multichannel signals to include in the next update of ELSE.

I have a working "pick~" object that picks a single channel from a multichannel connection. Of course you can set which channel with a message.

I'm now expanding this concept to remap or reorder a multichannel signal, much like how you can reorder a list message in Pd with dollar symbols ($1, $2, etc). It is called "remap~" for now and takes floats or lists. A "0" means "none", so no channel is picked and we get zeros. With a float input or argument it is just like "pick~".

It is working well depending on the list I am sending, but somehow it doesn't work for other lists.

here's the "dsp" code.

static void remap_dsp(t_remap *x, t_signal **sp){

    signal_setmultiout(&sp[1], x->x_n);

    int length = sp[0]->s_length;

    for(int i = 0; i < x->x_n; i++){

        int ch = x->x_vec[i].a_w.w_float;

        if(ch > sp[0]->s_nchans)

            ch = sp[0]->s_nchans;

        if(ch >= 0)

            dsp_add_copy(sp[0]->s_vec + ch*length, sp[1]->s_vec + i*length, length);

        else

            dsp_add_zero(sp[1]->s_vec + i*length, length);

    }

}

If I print the "ch" values and ch*length or i_lenght I get the expected values, so I can't understand what goes wrong.

For instance, if I have a 4 channel connection input with values "1 2 3 4" and send it the list "1 2 3 2 1" I get the correct expected output of "1 2 3 2 1". If I send it "2 1", output is the same! Single float values also work as mentioned, now for some bugged outputs...

"3 2 1" gives me "3 2 3"

"1 1 2" gives me "1 1 1"

"1 2 2 3" gives me "1 2 2 2"

funny enough, something like "1 2 2 2 3" gives me the same correct output.

I can't see a pattern here. I need help from the wizards to please save me. Test patch attached. Code lives here https://github.com/porres/pd-else/blob/master/Code_source/Compiled/signal/remap~.c

thanks

ps. While we're at it, I don't get why we have both sp[0]->s_length and sp[0]->s_n, aren't both the same?

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