It reminded that I had actually rewritten (ported) some code that kind of generates them.
I was looking around being interested in digital painting and I thought it would be a good place to start by looking at what someone else was doing, and then do it better.
I found an OpenProcessing sketch http://www.openprocessing.org/sketch/4675
That produced some satisfying results once tweaked a little bit (images at the bottom).
I rewrote it in another language, developed a GLSL shader for the threshold effect and optimised it so that it ran significantly faster on slower machines (order of magnitude increase), the extra speed made it more satisfying as I was able to keep the effect and the movement was more fluid.
I then went one step further and created multiple layers of a GLSL noise warp shader (the thing that warps everything a a bit) at different frequencies, this gives the video a kid of inkblotty effect that I really like and so I've included this in my global bank of shader combinations and fx. I've linked a video of this effect at the bottom.
The next thing that I would like to experiment with is using a harmonic relationship with the noise frequencies rather than a linear one. Currently the frequencies go from { 1 - 16 } in steps of one, and I would rather they go something like { 4 (32/8), 4.514285714... (32/7), 5.333... (32/6), 6.4 (32/5), 8 (32/4), 10.666... (32/3), 16.0 (32/2), 32 (32/1) } . My reasoning for this is that I read about (and have used before) this thing called "harmonic noise", but up until doing this project I had not considered what that actually means.
I would also like to experiment with changing the speed of the noise movement, as I think that the movement of the finer grain noise is too high (I suppose I could make it zero).