A bit more than one year ago I have introduced my ideas in a thread on the RawTherapee forum, which you can read here:
http://rawtherapee.com/forum/viewtopic.php?f=9&t=4659&start=30#p37242
but the initial momentum dropped down rather quickly… In any case, I have spent really a lot of time studying RT and DT source code to see where my ideas could fit in, and at the end I gave up due to the inherent architectural differences between what I had in mind and the existing code.
Basically speaking, I wanted to create a tool that works non-destructively on layers, and the fixed pipeline architecture of RT and DT make this almost impossible to achieve without a huge re-writing of the pixel pipeline. By the way, this point of view has also been expressed by the RT developers in the thread I quote above.
Believe me, I have hesitated very long before starting a project from scratch, and I’ve actually started coding only when I discovered the VIPS library, as it provided exactly what I needed to implement the core processing pipeline (low memory requirements, automatic parallelization of processing, a really flexible interface for combining processing operations, better than GEGL IMHO, etc…).
Last but not least, I’m not really an image processing expert. I’ve actually not invented anything new in my program, instead I’ve put together existing code inside a different processing structure…
“is it relevant to create another raw image processing program?”
Non-destructive layer-based processing is being expected from GIMP since many years, and seems yet far to come… I claim that PhotoFlow does that already, directly on RAW images if you need to, in a rudimental but already quite efficient way.
To summarize: unless I completely give up the idea of layer-based processing, I unfortunately do not see for the moment a way to directly contribute in DT or RT. However, this might also come from my limited knowledge of their respective source codes, so I am open to any suggestion that could reduce the amount of code I need to write and debug!
By the way, would the DT developers be ready to modify the processing pipeline such that layer editing could become possible? VIPS would have in this case lots of things to offer…