As far as I can tell, PhotoFlow lets you create any linear sequence of pipeline stages.
But sometimes I want two branches based on the same source layer. For example, should Filmulation make its way in, sometimes I’d want to use one strong, large film area filmulation setting for a uniform dark region and a weaker, small film area filmulation for the adjacent sky to reduce the haloing visibility.
Or, I might want to use two demosaicing methods, like LMMSE in the shadows and uniform areas and AMaZE for highlights and along high chroma change edges.
To this end, could there be a layer that says “Grab the data from x layers below”? For example, you’d have LMMSE first, then a full opacity “look 2 layers down”, then AMaZE, then a masked “look 3 layers down” that selects for the uniform and darker areas to pull from the LMMSE output.
PhF has a tool called “clone layer”, which allows to duplicate the output of a given layer (or of one of its channels) anywhere in the layer stack (provided that the clone is above the copied layer).
The cloning is done on-the-fly, which means that if the original layer changes, the clone layer immediately reflects those changes. Moreover, no actual “copy” is performed, instead the memory area of the original layer is re-used for the cloned layer.
Since in PhF the RAW loading and RAW processing are performed by two separate tools, it is possible to clone the RAW data layer and put a second RAW processing layer above the clone, with different RAW processing parameters (WB, exposure, demosaicing, etc…). The second processing can then be combined with the initial one through a layer mask, either based on a gradient, path selection, luminosity or more…
Here is an example of what I am talking about: http://filebin.net/zt65gik5jo
It basically shows what you are asking, I guess.
For the future I plan to simplify the layer lining mechanism: each tool will give the possibility to take its input from either the layer below it or a specific layer.
In this respect, PhF is actually not a lyre-based editor, but more a node-based one.