Simulated Slime Mold

Made with Houdini 18, Spring 2020



Physarum polycephalum is a slime mold, an organism made of a network of tubes that can grow and move across surfaces. They appear similar to fungi but are made of amoeba that have fused together. This project was an exercise in simulation and organic growth using Houdini, to recreate the appearance of physarum at micro- and macroscopic perspectives. First I tried using [link href="https://www.sagejenson.com/physarum"]Sage Jenson's implementation[/link], which resulted in very accurate particle simulation. However, it didn't translate to 3D very well, so I ended up using a voronoi fracture-and-trace method. This method creates splines which can be swept along with geometry and used to drive particle simulation along the network's paths.







The "grown" geometry is also used to create the microscopic view with a different set of shaders and additional animated geometry within the paths.









Breakdown

Mold Growth




The growth in this method is simply tracing a predefined path. The network of paths is created by fracturing the input geometry into voronoi cells. Then, find the shortest path between one or more start and end points within the network. Finally, trace the lines to simulate growth.





Cell Flow




The cell flow through the physarum is created by sweeping a tube along the paths of the network. Those tubes are turned into a volume, points are scattered along the network, and the tangent of the paths are used as a vector for the points to travel. Geometry can then be copied to the points with randomized attributes per point.





Houdini Shaders




The surface of the physarum is created with a mixture of noise displacement and fresnel opacity. A soft alligator noise is used to create the bumpy surface, and the camera angle-based transparency is used to simulate the effect of looking through a microscope at a membrane.