Diffusion Effects in Houdini

Houdini FX

A research project about Reaction Diffusion patterns in Houdini. Below is the final edit of the results I came up with using Houdini. Enjoy!

In nature this kind of diffusion happens as a reaction between two chemicals. Animal patterns, such as those on zebras and giraffes are probably the most recognizable instances of reaction diffusion. The mathematical formula for these kind of effects involves the Laplacian function, which is also used for blurring pixels (2D) or voxels (3D). So instead of implementing this complex formula I used blurring as my method of diffusion.

I started of in 2D. The basic steps are as follows: you start with a certain amount of “chemicals” A and B, you diffuse or blur them together, and then redefine the edges by increasing the contrast. Redo these steps multiple times and you get intricate diffusion patterns!

In 3D we apply the same steps but on volumes (a fog entity made up of voxels). We start from a seedpoint and grow the effect outwards and can contain the effect within other shapes. This is just another volume that we multiply with the diffusion volume, anything outside this boundary volume will be multiplied by zero and therefore be deleted. The result is a growing diffusion effect following the same principles as before, only now it’s in 3D.

We can vary the effect by changing the blur values or the strength with which the edges get contrasted. Some examples: