viewdirs vs direction in cast_rays

[bring728]

Hi! Thank you for your wonderful work.

I have a question about https://github.com/SuLvXiangXin/zipnerf-pytorch/blob/4de3d21ebb9e15412d36951b56e2d713fddd812b/internal/render.py#L146 this function. Why do you use the directions vector instead of the normalized vector viewdir? I guess basis_matrix should be a rotation matrix and each column should be a normalized vector. So shouldn't I use viewdir instead of directions?