I was wondering if / how this is possible in Blender.
Shaders in game engines like unity and unreal read texcoords (aka UVs) as Vector4 properties. Blender seems to deal with these mostly as Vector2.. however this can be quite useful.
For example I have packed a different set of vertex normals into the UV2 texcoord using code in unity but that approach is quite cumbersome and not as flexible as doing it in blender when really working the model.
How can I put a Vector3 information into a uvmap / texcoord?
(this would also allow multiple vertex color sets in an exported fbx).
thanks for your answers.
UV coordinates in Blender are 2d vectors. As far as I can tell, they can only be 2d vectors and it' not possible to change that. You can have a few of them. But you should probably find a more appropriate place to store the data you need. Blender supports various vertex attributes:
You can manipulate them from the Python API:
There are formats meant for exchanging data between different software like Alembic that do support custom attributes. You could look into this for exporting and importing the data.