This is a really simple SOP built with the HDK for creating the Mandelbulb. I compiled against Houdini 19.0.702 on Windows, but it should be possible to get it working using hcustom on linux without too much difficulty.
The Mandelbulb is a beautiful and fascinating 3D fractal object which is related to the Mandelbrot set. I cribbed the formula used in this code from https://www.skytopia.com/project/fractal/2mandelbulb.html#formula.
The SOP generates a volume of size (64,64,64) by default which can be resized as required. It also supports transformation of the co-ordinate system before it gets input to the Mandelbulb formula, which is a good way to zoom in on areas of interest without dialing up the resolution to non-interactive levels.
I would recommend leaving the multi-threaded toggle ticked for better performance.
