[PD-dev] difference between t_canvas and t_pd

Rich E reakinator at gmail.com
Tue Feb 8 10:47:59 CET 2011


That makes sense, all except the names. :)  Nice docs.

On Tue, Feb 8, 2011 at 6:33 AM, Hans-Christoph Steiner <hans at at.or.at>wrote:

>
> t_canvas is now just a t_glist.  a t_glist is a list of objects that
> represents a patch, here's what I wrote about it a while back:
>
> http://wiki.puredata.info/en/glist
>
> I am pretty sure that t_pd is a generic class pointer, like a pointer to
> Object in Java.
>
> .hc
>
> On Feb 6, 2011, at 2:15 AM, Rich E wrote:
>
> Update to this: it seems that I can just use t_pd pointers to open and
> close the patches, although I still need to return the t_pd *x pointer from
> glob_evalfile().  I don't know which method is best for opening/closing,
> with t_canvas or t_pd..
>
> The new methods look like this:
>
> t_pd *glob_evalfile(t_pd *ignore, t_symbol *name, t_symbol *dir)
> {
>     t_pd *x = 0;
>     t_pd *x_loaded = 0;
>
> /* even though binbuf_evalfile appears to take care of dspstate,
>  we have to do it again here, because canvas_startdsp() assumes
>  that all toplevel canvases are visible.  LATER check if this
>  is still necessary -- probably not. */
>      int dspstate = canvas_suspend_dsp();
>     binbuf_evalfile(name, dir);
>      while ((x != s__X.s_thing) && (x = s__X.s_thing))
>     {
> vmess(x, gensym("pop"), "i", 1);
> x_loaded = x;
>     }
>     pd_doloadbang();
>     canvas_resume_dsp(dspstate);
>     return x_loaded;
> }
>
> t_pd *libpd_openfile(const char *basename, const char *dirname) {
>  t_pd *x = glob_evalfile(0, gensym(basename), gensym(dirname));
>  pd_pushsym(x);
>  int dzero = canvas_getdollarzero();
> pd_popsym(x);
>
> return x;
> }
>
> void libpd_closefile(t_pd *x) {
> pd_free(x);
> }
>
>
> I would appreciate any feedback/suggestions from you guys who know the pd
> API much, much more thoroughly that myself.
>
> Cheers,
> Rich
>
> On Sun, Feb 6, 2011 at 4:49 PM, Rich E <reakinator at gmail.com> wrote:
>
>> I can't remember, are questions related to pd's C API appropriate for
>> pd-list, or are they better asked here?  It seems that everyone who responds
>> to those questions is on this list just as much, anyway.
>>
>> I have been mucking around with opening and closing pd patches using API
>> calls instead of pd's messaging system.  The reason for this is that I would
>> like to be able to manage (open/close) multiple instances of a patch, and be
>> able to send each copy of the patch a unique message via its $0 argument
>> (see http://www.mail-archive.com/pd-list@iem.at/msg41648.html).  So far,
>> the method has been to hack glob_evalfile to look like:
>>
>> t_canvas *glob_evalfile(t_pd *ignore, t_symbol *name, t_symbol *dir)
>> {
>>     t_pd *x = 0;
>> /* even though binbuf_evalfile appears to take care of dspstate,
>>  we have to do it again here, because canvas_startdsp() assumes
>>  that all toplevel canvases are visible.  LATER check if this
>>  is still necessary -- probably not. */
>>     t_canvas *x_canvas = 0;
>>      int dspstate = canvas_suspend_dsp();
>>     binbuf_evalfile(name, dir);
>>  while ((x != s__X.s_thing) && (x = s__X.s_thing))
>> {
>> x_canvas = canvas_getcurrent();
>>  vmess(x, gensym("pop"), "i", 1);
>> }
>>     pd_doloadbang();
>>     canvas_resume_dsp(dspstate);
>>     return x_canvas;
>> }
>>
>> The only addition is that x_canvas is retrieved before x is 'popped' off
>> of pd's global stack, and is then returned, giving me a handle to close that
>> particular patch with something like:
>>
>> canvas_menuclose(x_canvas, 0);
>>
>> But I realize that in global_evalfile, t_pd and x_canvas point to the same
>> address space.  This leads me to ask, what is the difference between these
>> two pointers?  Is t_canvas a t_pd along with variables for its graphical
>> nature?
>>
>> Mathieu also pointed to me (as I was using the first set of these) that
>> canvas_setcurrent() and canvas_unsetcurrent() are aliases of pd_pushsym()
>> and pd_popsym().  Is there a good reason to use one over the other?
>>
>> Last question:  Does anyone see a way that I could get the value of x in
>> glob_evalfile above without changing the function?  I don't think it is a
>> dangerous change (and it looks like I could just hand x.gl_pd to
>> canvas_menuclose, thereby not really needing a t_canvas pointer), but I
>> would of course prefer to not change the API if possible.
>>
>> Cheers,
>> Rich
>>
>
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