[PD-dev] Re: garray_update

[Mathieu Bouchard]

On Fri, 5 Aug 2005, Tim Blechmann wrote:
> > In general, the question of scheduling graphics updates is hard,
> > especially now that (arrays can contain (lists that contain (arrays of
> > scalars))), etc. Having "garrays" separate from the "real" data
> > structure mechanism was always a temporary measure, and now I'm glad
> > it's gone.  But what this means is that now we need a more general way
> > of updating changes to data. If I can think of a good one I'll get it
> > into 0.39 (it's prety high on the dolist at the moment...)
> before i'm starting to work on an implementation on my own ... have you
> been thinking about this?

I propose something like this:

typedef void (*t_garray_observer)(t_garray*,int start,int length);
void garray_add_observer(t_garray*,t_garray_observer);
void garray_del_observer(t_garray*,t_garray_observer);
void garray_notify(t_garray*self,int start,int length) {
  self->observer(self,start,length);
}

such that the add and del functions maintain a list of observers to notify 
when a change is being applied.

the garray objects call garray_notify method just _after_ every change 
they make to the data, to indicate the span of data that has been 
modified: that is, the start index, and the number of entries that have 
been modified.

any piece of code that is external to a garray but modifies its data
directly instead of through the object's method, must now call
garray_notify as if it were the garray object itself. that's the difficult
part because it means incompatibility with the objects that may have 
modified the data silently.

does that make sense?

I'd like a more general mechanism than that, which may apply to all pd 
objects, such as:

typedef void (*t_pd_observer)(t_pd*);
void pd_add_observer(t_pd*,t_pd_observer);
void pd_del_observer(t_pd*,t_pd_observer);
void pd_notify(t_pd*,...);

This is something being suggested by the IMPD paper presented last year at 
PdConvention04:

    http://artengine.ca/matju/graz/ImpureData_PdConvention04.pdf

In section 1.1; it's just that the one above is more flexible, as it can 
apply to parts of objects instead of just wholes.

However I'll have to think some more about how the "..." part would work, 
because varargs in C/C++ are a bit clumsy to use...

____________________________________________________________________
Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
Freelance Digital Arts Engineer, Montréal QC Canada