[PD] Any problems else/blocksize changing subpatch blocking during dsp?

Charles Z Henry czhenry at gmail.com
Fri Jan 17 07:36:19 CET 2020

On Thu, Jan 16, 2020 at 1:03 PM Christof Ressi <christof.ressi at gmx.at> wrote:
> it's certainly not a good idea to (possibly) modify the DSP graph while it's being built.

Or a *great* idea

>As I said, the external should use a clock to schedule the message for the next tick.

Here's what seems possible:
The canvas "dsp" method gets called on toplevel canvases.  It adds all
the objects in the canvas with "dsp" methods to an unsorted list.
Then, in ugen_done_graph, the main work of setting up the dspcontext
struct from block~/switch~ happens.  It allocates all the signals, and
ugen_doit puts each chain of objects in a queue to have their "dsp"
methods run.  Then it finally reaches a sub-patch (a canvas object),
and its "dsp" method gets called.

The outcome depends on which runs first--the blocksize~ "dsp" method
or the sub-patch canvas "dsp" method.  Sub-patch blocksizes could
still be set, during graph generation, because the block~ parameters
aren't even relevant until the sub-patch "dsp" method.

With no signal inlets and no outlets, there's nothing there to force
it to come before/after the sub-patch "dsp" method.

If blocksize~ had a signal inlet, you could connect it to a subpatch
output and be guaranteed that the sub-patch "dsp" method will be
called before the blocksize~ "dsp"

And vice versa (the interesting case): if blocksize~ has a signal
outlet connected to some sub-patch inlet, then it's possible to set
the sub-patch block~/switch~ parameters during the graph generation,
right before they are to be used.
But.... I still have questions.  Will the block~ "set" method trigger
the dsp graph to be rebuilt, at some point when it's already trying to
build the graph?  What would happen if it did?

> > Gesendet: Donnerstag, 16. Januar 2020 um 19:07 Uhr
> > Von: "Charles Z Henry" <czhenry at gmail.com>
> > An: Pd-List <pd-list at lists.iem.at>
> > Betreff: Re: [PD] Any problems else/blocksize changing subpatch blocking during dsp?
> >
> > On Thu, Jan 16, 2020 at 10:03 AM Christof Ressi <christof.ressi at gmx.at> wrote:
> > >
> > > I also think that messaging an outlet in the "dsp" method is not a good idea and it's better to use a clock with delay 0. The user might take the output of [blocksize~] and accidentally do something which interferes with DSP graph generation, e.g. by resizing an array, creating/deleting objects, etc.
> > >
> > > Christof
> >
> > Yes it *could*, but I'm unclear on the timing.  I've read and
> > consulted the d_ugen.c code recently but .  The block parameters are
> > derived from block/switch and coded into the dspcontext struct which
> > gets generated for each canvas.  The parameters have to be known
> > before "dsp" gets called in the current canvas (which would trigger
> > the "blocksize~" output), but is the sub-patch dspcontext already
> > built?  I'll try to follow up later today and try to answer it
> >
> > That ambiguity could be resolved by looking at the "bang~" code.  I
> > just think it's an interesting question what is possible to happen as
> > it is currently written
> >
> > bang~ sends properly timed messages by using:
> > t_clock *x_clock;  //in the data structure
> >
> > x->x_clock = clock_new(x, (t_method)bang_tilde_tick); // in the "new" method
> >
> > static void bang_tilde_tick(t_bang *x)  // added "tick" method
> > { outlet_bang(x->x_obj.ob_outlet); }
> >
> > and
> > clock_delay(x->x_clock, 0);  // in the "perform" routine
> >
> > Chuck
> >
> >
> >
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