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 adrcki@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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