I've been searching for a way to replicate Arcview's flow length method (http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Flow%20Length) for a plugin I am developing; more specifically calculating the DOWNSLOPE distance along the flow path, from each cell to a sink or outlet while using a WEIGHT RASTER as well. It doesn't seem like there are any built in functions in Mapwingeoproc.hydrology for doing this if I'm not mistaken (there only seems to be methods for calculating the UPSLOPE flow lengths).
Are there are any preexisting plugins or alternate ways of doing this? Any help would be greatly appreciated.
1) add a request to Mantis bug tracer [bugs.mapwindow.org] (I'm also interested in it but I've no time to implement it at the moment)
2) try to build your function: you have to see the tardemlib code here [svn.mapwindow.org] (e.g. look for 'dists' function).
The algorithm is implemented recursively, I hope it will be of some help.