[PD-dev] difference between t_canvas and t_pd

[Hans-Christoph Steiner]

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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