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?
s_length is just a more descriptive alias for s_n.
Christof
On 22.07.2023 20:52, Alexandre Torres Porres wrote:
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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