A 2-D slice of one component of 3-D "psrdnoise", computed on the rotated "Perlin grid" to avoid strong grid artefacts in the axis-aligned slice.
The animation comes both from a translation along z and from the rotating gradients. The pattern is tiled once across the canvas, i.e. it wraps around at the edges. The translation in z makes it possible to perform animations that don't repeat, or that repeat with a longer and less conspicuous period than the rotation alone. It does, however, result in a different pattern than 2-D noise. Specifically, this pattern has considerable amounts of low frequency content.