By using setTexcoordScaleOffset on the material and aligning the UV's of all the models it seems so that the river continuasly flows.
The assets were buried in a pile of stuff in some test dungeon (along with the blocking army that me and Isaac created last year that we never did anything with, but that is another story
) I tried to clean them up lua wise and created a single demo map that can be opened in the editor.
This is released "as is" it was never meant to fit every scenario, feel free to take it apart, modify it to fit your needs or use as is.
https://www.nexusmods.com/legendofgrimrock2/mods/111
kind regards.
Skuggasveinn.
