[PD] [tabwrite4~], is it possible at all?

[Mathieu Bouchard]

Le 2012-01-07 à 11:01:00, katja a écrit :

> It seems to me that 4-point-interpolated writing would mean: write
> values to 4 indexes at a time, just like [tabread4~] reads from 4
> indexes at a time.

I don't think that [tabread4~] can be reversed so easily. I think that the 
most appropriate antialiased [tabwrite4~] would not be a mirror image of 
what [tabread4~] is. It wouldn't necessarily write four values : making it 
write two values would be quite normal ; you'll want to tune its amount of 
«opaqueness» perhaps, and this will be a setting for which you will have 
no ideal default value ; and whatever it'll be, you probably won't like 
that it's not a mirror image of [tabread4~] or even of [tabread~].

This makes me think of [#remap_image] and [#store]. If I want to warp the 
coordinates of a picture in a nontrivial way, I can't loop over the source 
pixels and write them in the destination image, because this creates lots 
of holes. It doesn't tell what to fill the holes with. What [#remap_image] 
does (using the [#store] external) is to loop over destination pixels and 
choose where their data come from. This means that the warping function 
has to be inversed.

nontrivial examples :
http://gridflow.ca/gallery/un_sur_z%C3%A8de.jpg
http://gridflow.ca/gallery/patch_dans_patch_5.png
http://gridflow.ca/gallery/patch_dans_patch_9.png

help :
http://gridflow.ca/help/%23remap_image-help.html

But when the source data is a continuous flow, you can't index it as if it 
were a picture of pixels, because the flow of sound is unlimited and 
realtime.

IMHO, it's a hard problem. It looks like the kind of thing for which many 
situation-specific solutions are designed because there is no general way 
to make something that generally makes sense.

> While writing 4 values, recently written values must be taken into 
> account, not bluntly overwritten. So two existing values, x[n-2] and 
> x[n-1], should be somehow integrated with new values, if the writing 
> direction is positive.

Just think about constant speeds for now : if the index is a phasor 
moving at the same speed as [tabsend~] would, then it better act very 
similar to [tabsend~]. This is the first thing you ought to verify for any 
possible solution. Then you should look at what happens when using any 
other different constant speeds. Then if you are satisfied with what 
happens with all constant speeds, chances are that you will be satisfied 
with variable speeds.

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| Mathieu BOUCHARD ----- téléphone : +1.514.383.3801 ----- Montréal, QC