as for only weaving: that's triggered with the "-quick" option and is quite straight forward. the resulting cache will be ~10MB
however you'll still have to compile the shaders later on
if you want to change the target hardware to use in the actual output cache if you don't use quick: you can edit the profiles that are targeted in data/config/shadermgr.cfg
usage in general is: /path/to/shagnetron /shader/ [-quick]
also note that you can only pre-compile a specific shader if you use /shader/folder/name.xml instead, e.g. /path/to/shagnetron /shader/terrain/alphasplat.xml
