[PD-dev] difference between t_canvas and t_pd
Hans-Christoph Steiner
hans at at.or.at
Mon Feb 7 20:33:15 CET 2011
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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