Bone groups and layers importing albam.engines.mtframework.Mod156

[Brachi]

Mod156 has a field called unk_13 that is a fixed array of 256 bytes. It turns out it's actually a mapping used for animations. Apparently, every index represents a hard-coded bone type.
For example, based on uPl00ChrisNormal.arc->pl0000.mod and uPl01ShebaNormal.arc->pl0100.mod, indices 16 and 20 represent the upper left and right leg respectively. This can be confirmed parsing both mod files and taking the bone indices visually when they were imported:

>>> from albam.engines.mtframework import Mod156
>>> mod = Mod156('pl0000.mod')
>>> mod2 = Mod156('pl0100.mod')
>>> chris_right_leg = 112  # taken from blender
>>> chris_left_leg = 117
>>> sheva_right_leg = 2
>>> sheva_left_leg = 8
>>> assert list(mod.unk_13).index(chris_right_leg) == list(mod2.unk_13).index(sheva_right_leg)
>>> assert list(mod.unk_13).index(chris_left_leg) == list(mod2.unk_13).index(sheva_left_leg)

Knowing this, it would be useful for modding to classify them all and create bone groups and layers.
For example, the first layer should include the most important bone: spine, legs, arms, head bone, etc.
This way, automatic weighting can also be done in layers, refining or omitting more detailed bones.