Long time ago I implemented [dinlet~] (in moonlib) , aka "default inlet~":
when the dinlet~ isn't connected, then it reverts to its default (constant)
signal value, which is given as an argument.
Maybe reading the code could give you some ideas:
https://github.com/MetaluNet/moonlib/blob/externals/moonlib/dinlet~.c



Antoine Rousseau
  http://www.metalu.net <http://metalu.net> __
http://www.metaluachahuter.com/
<http://www.metaluachahuter.com/compagnies/al1-ant1/>


2018-03-06 18:31 GMT+01:00 Alex <x37v.a...@gmail.com>:

> I put up a related 'enhancement' PR a bit ago for [inlet~]
> https://github.com/pure-data/pure-data/issues/259
>
> I dug into the ugen graph code a bit and got lost trying to implement it
> myself..
>
> On Tue, Mar 6, 2018 at 9:22 AM, Miller Puckette <m...@ucsd.edu> wrote:
>
>> This too is on my (almost infinitely long) dolist... to somehow extend the
>> "dsp" message to allow objects to find out whether there are signals
>> connected
>> or not (and perhaps also to be able to deal with unequal-sized arrays
>> somehow).
>>
>> Main reason I think this is needed is so that objects like "vcf~" can take
>> audio signals to change "q" without always assuming they're audio (which
>> would cause more overhead).
>>
>> cheers
>> Miller
>>
>> On Tue, Mar 06, 2018 at 05:12:37PM +0100, Christof Ressi wrote:
>> > the object doesn't know but the ugen graph algorithm does. if it sees
>> that a signal inlet is not connected it creates a new signal and adds a
>> scalar copy routine to the DSP chain.
>> > the scalar value is stored in the inletunion in struct _inlet (m_obj.c)
>> and it's updated whenever you send a float message to the inlet.
>> > the first inlet is somewhat special in that you can use the
>> CLASS_MAINSIGNALIN macro to store the scalar value directly in the class
>> (usually named x_f).
>> >
>> > have a look at ugen_doit in d_ugen.c:
>> >
>> > if (!uin->i_nconnect)
>> > {
>> >     t_float *scalar;
>> >     s3 = signal_new(dc->dc_calcsize, dc->dc_srate);
>> >     /* post("%s: unconnected signal inlet set to zero",
>> >        class_getname(u->u_obj->ob_pd)); */
>> >     if ((scalar = obj_findsignalscalar(u->u_obj, i)))
>> >         dsp_add_scalarcopy(scalar, s3->s_vec, s3->s_n);
>> >     else
>> >         dsp_add_zero(s3->s_vec, s3->s_n);
>> >     uin->i_signal = s3;
>> >     s3->s_refcount = 1;
>> > }
>> >
>> >
>> > > Gesendet: Dienstag, 06. März 2018 um 16:08 Uhr
>> > > Von: Alexandros <adr...@gmail.com>
>> > > An: Pd-List <pd-list@lists.iem.at>
>> > > Betreff: [PD] How can a signal inlet of an object know if it's
>> receiving a signal
>> > >
>> > > [phasor~] ([osc~], and probably other objects too) seems to be aware
>> of
>> > > signals being connected to its left-most inlet. Providing an argument
>> to
>> > > [phasor~], if there's no signal coming in its inlet, it will use its
>> > > argument for the frequency. As soon as a signal is connected, it will
>> > > use that signal for its frequency. As soon as this signal gets
>> > > disconnected (even if the signal is 0), [phasor~] will go back to
>> using
>> > > its argument for its frequency.
>> > >
>> > > Reading [phasor~]'s code in d_osc.c, I can't understand how this is
>> > > achieved. I thought of looking into canvasconnections.c from the
>> iemguts
>> > > library, but it's a bit too complicated for me. Still, there's this
>> > > comment in that file:
>> > >
>> > > /* as Pd does not have any information about connections to inlets,
>> > >      * we have to find out ourselves
>> > >      * this is done by traversing all objects in the canvas and try
>> > >      * to find out, whether they are connected to us!
>> > >      */
>> > >
>> > > Does this have to do with control inlets only? How can [phasor~] know
>> if
>> > > it's receiving a singal in its frequency inlet?
>> > >
>> > >
>> > >
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