Disney’s upcoming animated film Frozen is hitting theaters in just a few days, and the company’s animation gurus have posted a quick video explainer that goes over how Frozen’s snow effects were created. It’s not as simple as just rendering one big monolithic snowball at a time — the animations in Frozen take into account tiny particles by leveraging massive computing resources.
Snow is a difficult substance to simulate in animations — it is solid in that it’s frozen water, but differing levels of moisture can make it behave in different ways. The existing techniques for replicating fluids don’t really make sense either because snow can be packed into solid clumps (or snowballs in the common vernacular). Disney animators instead worked from the most basic level up by using a hybrid Eulerian/Lagrangian Material Point Method.
The Material Point Method starts with very small particles of snow, which are assigned volumes and masses in a virtual grid. The model then factors in velocities and collision variables for each particle, which is then used to output vectors. The model then moves back to dealing with particles, applying the calculations from the vectors to get updated positions for each particle. This detailed rendering would not have been feasible in past years with more limited computing horsepower.
By varying each of these factors, the particles move differently and can simulate heavy wet snow that sticks to things, or dry powdery snow that swirls around with the wind. The result is an incredibly believable model of snow behavior in Frozen. Animators worked closely with the writers to more effectively use this realistic snow rendering in the movie’s storyline. Judging from the demonstrations in the video above, the snow will be an effective storytelling tool.
Frozen is out November 27th, and you can check out the trailer below for a fuller understanding of the work that went into all that snow.