Researchers crack the code for simulating mud in computer graphics

Whether you're wandering a lush landscape in a videogame or are engrossed in a movie with realistic CG effects, it can be easy to take the underlying technology for granted. Of course, there is a lot going on from a technical standpoint and while developers and animators have gotten pretty good at simulating water and sand, combing the two into mud has been especially challenging. That might be about to change.

Researchers from UCLA, DreamWorks Animation, Jixie Effects, and the University of Pennsylvania will be presenting a paper at the Siggraph 2017 conference this July outlining their research into altering the properties of simulated sand when simulated liquid is introduced.

This is no small feat. Simulating the simple task of flipping over an hourglass filled with sand sets in motion a complex chain reaction as millions of particles bump into one another and eventually pour into the bottom. There are millions of calculations taking place every second.

Adding water obviously changes things, and it's difficult to simulate with computer graphics what happens when water and sand mix. Or more accurately, it's difficult to realistically simulate the transformation into mud.

"The novel aspect of this new work is the modeling of detailed physical interactions between water and sand," assistant professor Chenfanfu Jiang of the Computer and Information Science Departments at the University of Pennsylvania told Gizmodo. "Technically, we use particles to represent individual grains of sand and water droplets. In each simulation time step, individual material responses as well as the interaction force between sand and water are computed."

The process is aided by a voxel grid, basically a 3D bitmap. Jiang says the combination of particles and grids "allows elegant modeling of material interactions, which was very challenging with many other methods."

It remains to be seen if this fancy new mud tech will eventually make its way into videogames, but it's certainly fun to think about. As hardware gets more and more powerful, games are becoming increasingly able to simulate real-world physics and behavior instead of merely creating the gamey simulacra that we're used to. 

There is plenty more to sink into in the paper (PDF).