[PD-dev] pointers

[Charles Henry]

On 7/8/07, Mathieu Bouchard <matju at artengine.ca> wrote:
> On Sat, 7 Jul 2007, Charles Henry wrote:
>
> > I was wondering if you could clarify for me what types of data
> > structures you are pointing to, because I could think of an application
> > that this would solve.
>
> In modern GridFlow, "grid" messages (the only special messages in
> GridFlow) contain one single fake pointer which is always pointing to a
> GridOutlet structure. When an object receives that, it calls ->callback(x)
> on the structure, where x has to be a GridInlet*. This subscribes the
> GridInlet to the streaming that will be performed by the GridOutlet as
> soon as the message handler returns.

I think I understand now.  You pass pointers to structures.  That
makes a lot of sense.

> As of now, this is always ever done by grid.c, so actual grid-handling
> pd classes named like [#whatever] never know about this and it could
> actually change from version to version (and it did). When patching, you
> are not allowed to assume anything about the contents of the grid message.
>
> > For a while now, I was wondering how to include a wave packets
> > transform in pd.  The wave++ library has a wave packets transform,
> > where the structure of the transform is provided as a tree, and the
> > tree is a class.
>
> We've had an experimental datatype in LTI (a C++ library wrapped by
> GridFlow) for pointing to special (non-gridoutlet) structs like that but
> it's not like we're so proud of it.
>
> Btw, if that's a balanced tree, it's rather easy to flatten it into an
> array in a predictable way. You've thought about that? (Are you talking
> about wavelets?)

The wave packets transform is a wavelet transform, in which each of
the branches with greater than 1 point can be expaned in the same
manner.  The big idea of using one is to do a best basis search, which
depends on the signal characteristics.  So, the best basis can be
drastically different from one signal to another.
I am sure there is a way to flatten the tree into an array, with
various extra parameters that tell you how to traverse the tree as
moving to different indexes of the array.  You're certainly correct.
I really hadn't thought of that before.
The existing wave++ library has functions on classes.  So to flatten
the tree for passing, only to be un-flattened afterwards is less
efficient than to pass a pointer to the tree.

But really.....
it's a pretty impractical example
there would be little need to have these specialized structures as
externals, to be passed to other externals.  A series of objects that
perform some kind of wave packets analysis/processing would only be
compatible with each other.  If you wanted to do some kind of
processing on the packets, you would have to write another external
for it, just to decode the structure anyway.  It's really just a
curiosity (as far as I can tell)
Thanks for describing to me how you pass "fake" pointers :)

Chuck