Upload 6 faces. Images will be center-cropped to squares and rescaled to the nearest Power of 2.
Filenames must contain: posx, negx, posy, negy, posz, negz.
Fallback: If names don't match, they are sorted (e.g., 1.jpg, 2.jpg) and assigned: negx, posx, negy, posy, posz, negz.