OK, at last I got a little time to go further with the rolling blinds thing.
I have partly found a way, but I haven't found THE way yet.
So my new theory is the following:
As mentioned before, the role changes diameter as the curtain gets rolled up and down. Unfortunately it is from the inside and out, and not from outside and in, and this is exactly what gives all the complications.
SO, I need to have two independant generators (Linear arrays). One for the roll, which is based on a helix and one for the straight part. As the role changes size, the other generator gets moved so that it fits with the outside of the roles diameter.
The two arrays has to work kind of opposite each other, so when the curtain rolles up, the roll get filled gradually filled with the straws along the helix path, and the straight part will get emptied of straws at the same time. Fortunately there is some newer functions in RC that make this possible, - the Start and End padding in the limits section.
So far so good. I have accomplished that - HOWEVER I must find a way to turn the roll as it gets filled, so the end is always staying at the same place, connecting to the straight part, - and there I am am BLANK how to accomplish that. At the same time I have no idea how to get the helix roll into a windows setup, - so that I can have individual length of closed curtain in a number of windows. I don't actually know if this is a blind end I am getting into.
Right now I can use it to produce a number of static preset lengths and then put it into another RC setup where I can either randomize it or handle it by paths mat ID.
I have made some screen dumps of my current solution shown with different states of rolling. As you can see the roll's end doesnt meet the end of the straight part.