This design was so interesting to me because it is the ultimate in do-it-yourself.
How I think it was achieved: There were drapery hold-back rings hung at the top corners of the windows, the kind used for scarf swags. In the ceiling, centered over the tub is another ring. I think the designer bought ready-made drapery panels and looped and swagged them through the rings. Some panels went side to side and some went corner to center. The effect was quite dramatic! And yet, I think it was probably a very cost effective treatment.
Here is another view. Ignore the creepy mannequin who's standing in the shower!!