Re: [Openexr-devel] Storing multiple layers in OpenEXR files

[Yves Poissant]

> Since a file's channels are already sorted alphabetically, it
> would not be a lot of work to add a method to class ChannelList
> that finds all channels whose names begin with with a  given
> prefix, e.g. "layername.":
>
>     void
>     ChannelList::channelsWithPrefix
>         (const char prefix[],
>          ConstIterator &first,
>          ConstIterator &last) const
>      {
>         first = last = _map.lower_bound (prefix);
>         int n = strlen (prefix);
>
>         while (last != end() && strncmp (last.name(), prefix, n) <= 0)
>             ++last;
>      }
>
> The function might be used like this:
>
>     ChannelList::ConstIterator first, last;
>     channels.channelsWithPrefix ("diffuse.", first, last);
>
>     for (ChannelList::constIterator i = first; i != last; ++i)
>         doSomethingWithChannel (i.channel());

I agree with this. If this was implemented in a next release, I would use it 
that way.

> > In one single string attribute. I llike that idea. And this would
> > certainly save file space.
> >
> > What about something like this :
> > "diffuse{R,G,B},ambiance{R,G,B},Z,tangent{X,Y},normal{X,Y}"
>
> I would prefer:
>
>     "diffuse,ambiance,Z,tangent,normal"

I have no problems with that if the above proposed new method is available.

> Or, even better, use an attribute whose value is a vector of strings,
> and store the names of the layers in the elements of the vector.

I did not know we had vector of strings attributes in OpenEXR. That would be 
the best approach. I'll look into that.

I guess we can expect the new channels retrieval method to be implemented 
and available in a future release, and I will have to change my code at this 
point to match the new method. In the meantime, since I don't want to change 
my code twice, I will keep my current code as it is for now.

Thanks,

Yves Poissant
Hash Inc.