Re: [Openexr-devel] Multi-layer multi-pass files

[Florian Kainz]

Ton Roosendaal wrote:
> Hi Florian,
>
> > Increasing the maximum length of channel names does break backwards
> > compatibility.
>
> Euh, I hope you mean upwards compatibility? :)

Older software will not be able to read files that contain
channels with long names.  Ideally, older software would still
read files with short names, even if they were generated by
new software.  If a file contains a long channel name, older
software should print a reasonable error message, rather than
announcing that the file is broken.


> While working on multilayer files I decided it would be very hard to  
> get a generic parser for a multilayer formatted exr file. There are too  
> many dependencies also with our internal conventions for reading and  
> saving, so I've tied it more to what is possible now in Blender (i.e.  
> the separation in "Layers", "Passes" and "Channels").
>
> In short the parsing goes as follows;
>
> - check for a comment in the file with string "Blender MultiChannel"
>
> [...]

Instead of overloading the "comments" attribute, I would suggest
adding another attribute, for example, a string attribute called
"BlenderMultiChannel".  This would leave the comments attribute
available for actual comments.

I guess for your scheme, only the presence of the BlenderMultiChannel
attribute would matter for now, but you could use it to store
additional information in the future.