pub fn fft_pad_box(full_dims: (usize, usize, usize)) -> CropBoxExpand description
A box covering the whole grid, each axis grown outward to an FFT-friendly size.
The accuracy-neutral half of this module: no data is discarded and the periodic boundary moves away from the object, so the only cost is the padded voxels. Worth doing whenever an axis has an awkward length — 339 = 3·113 costs about a third more transform time than 343 = 7³ despite holding fewer voxels.