Károly Zsolnai-Fehér explains how guide hairs can simulate thousands of individual strands efficiently. The technique lets hair interact with solid objects in real time, matching results from much slower full simulations.
400 guide hairs
150,000 total strands
August 29, 2016
Dear fellow scholars, this is two minute papers with. We have talked about fluid and cloth simulations earlier, but we never really set foot in the domain of hair simulations in the series to obtain some footage of virtual hair movement. Simulating the dynamics of hundreds of thousands of hair strands is clearly too time consuming and would be a flippant attempt to do so. If we do not wish to watch a simulation unfold with increasing dismay, as it would take hours of computation time to obtain just one second of footage, we have to come up with a cunning plan. A popular method to obtain detailed real time hair simulations is not to compute the trajectory of every single hair strand, but to have a small set of strands that we call guide hairs. For these guide hairs, we compute everything. However, since this is a sparse set of elements, we have to fill the gaps with a large number of hair strands and we essentially try to guess how these should move with based on the behavior of guide hairs near them. Essentially, one guide hair is responsible in guiding an entire batch or an entire braid of hair, if you will. This technique we like to call a reduced hair simulation, and the guessing part is often referred to as interpolation. And the question immediately arises, how many guide hairs do we use and how many total hair strands can we simulate with them without our customers finding out that we are essentially cheating? The selling point of this piece of work is that it uses only 400 guide hairs and leaning on them, it can simulate up to a Total number of 150,000 strands in real time. This leads to amazingly detailed hair simulations. My goodness, look at how beautiful these results are. Not only that, but as it is demonstrated quite aptly here, it can also faithfully handle rich interactions and collisions with other solid objects. For instance, we can simulate all kinds of combing or pulling our hair out, which is what most researchers do in their moments of great peril just before finding the solution to a difficult problem. Not only hair, but a researcher simulator, if you will. The results are compared to a full space simulation, which means simulating every single hair strand. And that is exactly as time consuming as it sounds. The results are very close to being indistinguishable, which was not the case for previous works that created false intersections where hair strands would erroneously go through solid objects. We can also stroke bunnies with our hair models in this truly amazing piece of work. These episodes are also available in early access for our Patreon supporters. We also have plenty of other neat perks. I've put a link in the description box. Make sure to have a look. Thanks for watching and for your generous support. And I'll see you next time.
