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A Material Point Method For Snow Simulation
- bhouston 13y agoThis is such a beautiful result. The simulation method used is Material Point Method, a technical that is used in engineering simulation but hasn't really been used much in Visual Effects. This will likely change now that there are these impressive results. The one issue I've seen people in the industry mention about this paper is that the the simulation times are quite long. https://en.wikipedia.org/wiki/Material_Point_Method https://en.wikipedia.org/wiki/Material_Point_Method
- batty 13y agoAgreed, very nice. I've heard the speed issue mentioned as well, although slow compared to what, I wonder? I don't see offhand any fundamental reason why it would be dramatically slower than, say, a standard FLIP-based fluid sim. It amounts to advecting Lagrangian particles combined with solving the elastoplasticity equations on a Cartesian grid, with a snow-specific constitutive model.
- bhouston 13y agoThere min/frame in the included paper chart range from 3.8m/frame to 25.8m/frame, which is pretty slow for 2013 at the simulation sizes they give. It is too bad they didn't break out the individual steps to show where the time was spent. Could simply be unoptimized code. I notice there is a restriction on the time step to be less than 0.5 x 10^-3 s, not sure if that is the main difference.
- tinco 13y ago0.5 * 10^-3s is 2000hz, so 20 iterations per frame, assuming they render at 100hz, that seems a bit on the high side.. does that mean they don't have a good way of interpolating the physics effects, does that happen a lot in these kinds of simulations? I work on a real-time multi-player game, and our physics step is actually larger than our framerate, we interpolate the rest, I guess that's quite the opposite of this :)
- chii 13y agoI dont know anything about rendering or simulations, but would this method be possible for real time rendering? or is it only applicable for offline rendered stuff (like movie sfx)?
- visakanv 13y agoI know very little about it too, but I think advances in video game visuals have shown that it's really just a matter of time. Check out Uncharted 3's real-time dynamic water effects: http://www.youtube.com/watch?v=BhzMR-vxYIk http://www.youtube.com/watch?v=BhzMR-vxYIk (Skip to about 2:50)
- PavlovsCat 13y ago> Skip to about 2:50 I think you meant to say 5:20 ^^
- tzakrajs 13y agoBattlefield 4 does a better job with real swells in the ocean allowing you to fight with boats using waves for cover.
- Zikes 13y agoAssassin's Creed 4 does something similar.
- nitrogen 13y agoI noticed some moments in that video where a flashing controller button appeared in the corner. Does that mean the player has to mash the button to continue? I hate games that do that. Why do game makers do that?
- visakanv 13y agoI suppose it makes you feel more involved, rather than just watching a bunch of cool cutscenes that you have nothing to do with (common in stylish Japanese RPGs like Devil May Cry, etc)
- moconnor 13y agoThe video is well worth watching. After several minutes of dry technical commentary, you suddenly get "Now we destroy a castle with a cannonball!" The snowballs colliding is extremely impressive.
- bilalq 13y agoThe guy talks way too fast though. I'm really struggling to understand what words he's saying. It almost feels like it's artificially accelerated. That being said, the visuals do indeed have a "wow" factor to them.
- mischanix 13y agoThe pdf linked [1] covers in-depth what the narrator is saying. [1] https://disney-animation.s3.amazonaws.com/uploads/production/publication_asset/72/asset/snow.pdf https://disney-animation.s3.amazonaws.com/uploads/production...
- berkut 13y agoIt's for Siggraph, so there's a time limit.
- pvarangot 13y agoIf you know what is Cauchy's stress tensor, know about finite element analysis, and grad classical mechanics, its understandable. If you don't know about that, you will not learn it in a demo...
- dakrisht 13y agoAmazing
- chaz 13y agoI don't know anything about graphics and simulation, but I'm always impressed with these SIGGRAPH demos. Here's the demo trailer for the papers from this year: http://www.youtube.com/watch?v=JAFhkdGtHck http://www.youtube.com/watch?v=JAFhkdGtHck (3 min)
- ByronFortescue 13y agoIt looks pretty good, but still, I think some of these examples look really foamy, and not like real snow. Not all physical behaviour is yet replicated I think.
- guardian5x 13y agoOf course not, its only a simulation of a model. The data necessary to store all physical attributes including every atom and sub-atomar particles would not fit on any hard disk in the world. The result is nonetheless pretty amazing.
- Dirlewanger 13y agoWe're getting there. Looks more like wet sand though.
- pistle 13y agoYou must have grown up with snow. My thoughts exactly. It fell into the uncanny valley for me... Sort of close, but then off in unnerving ways. Great work for where they got to, but it's not quite right yet.
- ihsw 13y agoAs someone that grew up with snow and been to a beach more than I'd care to admit, I can't help but agree that it's quite the uncanny valley. I'm sure Disney et al will find ways to distract you enough not to notice. I'm far more interested in seeing snow falling, especially with (for example) a street-lamp contrasting it. That would be something to marvel at.
- DannoHung 13y agoIt looks mostly right for wet snow. Powdery snow wouldn't work like this though. Maybe they just didn't think that example was very interesting?
- sparky 13y agoYeah, the paper talks about how to vary the parameters to simulate powder, wet snow, slush, etc. These techniques were developed for the movie Frozen, and to my eye (I grew up with snow too) they did a great job of simulating all manner of snow and ice.
- legacy2013 13y agoYea, powdery snow isn't all that hard to simulate (relatively) I believe. The snowflakes are just particles that are acted upon by an outside force( wind usually). I live and grew up in New England, and the snow in Frozen looks completely realistic. It's amazing the amount of work put into these movies. Most moviegoers won't realize what it took to simulate snow realistically, but the would have noticed if it was wrong.
- javindo 13y agoI was talking to my father in law (head of particle research for P&G) about particle simulation for research purposes and he was explaining the complex challenges with behaviour of interactions. It amazes me that even at the mathematical level, a post-doctorate doctor of chemical engineering with a team of physicists/computer scientists/mathematicians/chemists are still facing challenges which Disney seem to have solved - glad to see they are properly releasing this research!
- fsloth 13y agoThe requirements for a visual simulation and industrial process simulations are quite different.
- NamTaf 13y agoThis process yields fantastic, realistic visuals, but I bet you'd find it does not yield the scientific information they're chasing. It's sort of like how the 'standard' linear static finite element method assumes insignificant displacements and no plastic yielding of materials - as soon as you need to deal with any sort of significant level of displacement or distorsion of the material in question, a linear static solver isn't capable of giving you accurate results. With displacement, it tries to fake it by extrapolating the linear displacement and assumes that applies over the entirety of it, when in actual fact as soon as it displaces, the strain field in the material will change and it needs re-solving. It's a good tool, but it has its limitations.
- rschmitty 13y agoThis got no love before https://news.ycombinator.com/item?id=6780984 https://news.ycombinator.com/item?id=6780984 oddly
- GFischer 13y agoThis title is certainly more catchy. It's odd it didn't upvote the prior link.
- frogpelt 13y agoThere's probably a time limit on that function.
- GilbertErik 13y agoGoes to show how much a catchy title matters. :-/
- scott_s 13y agoThe front page of HN is like many other venues for what becomes popular: there is an enormous amount of randomness.
- joelthelion 13y agoIt's neat, but their snow looks more like old heavy snow than recent powder.
- atrus 13y agoEven better, that's what they were trying to simulate.
- gyom 13y agoExcept that, if it was what they wanted, then it's hard to explain the walking character at 3:30 that gets his legs almost trapped in the soft heavy melting snow. There's just no way that you'd get that kind of effect with that kind of snow. It looks more like the kind of thing that you'd get from non-uniform snow that has a crust on top (and that kind of snow is not sticky and not melting).
- xerophtye 13y agoWhat i really like about this is that instead of keeping it under wraps and calling it a "trade secret", they openly discussing their technique and releasing it for the advancement of the field. Not only did they write a paper about it, but made it open access! (as opposed to traditional journal publication)[1] So kudos to their effort! [1] Though this IS disney we're talking about and they certainly don't need journals for getting an audience for their papers
- berkut 13y agoMost of the VFX industry releases the majority of their techniques as papers, etc. Some of it's kept a secret, but that's happening less and less. There's a lot of competition, but still there's a lot of open stuff like OSL, OIIO, OCIO, OpenSubDiv that multiple facilities contribute to.
- Cort3z 13y agoComing from a snow-filled country I would say that this simulated snow behaves very close to the real deal. Very impressive
- clord 13y agoYep, but I'd qualify that: The demo seems to show wet snow (snowball snow) only. There are a few other types that happen around here, like dry snow, and crystallized snow. Dry snow is light fluffy stuff that doesn't pack. And crystallized snow is made of what feels like little daggers, behaving almost like ball bearings. But still, their result is brilliant!
- officemonkey 13y agoHave you seen "Frozen?" It really was a beautiful-looking film with lots of opportunities to show off the simulated snow they modeled.
- DoggettCK 13y agoBeautiful, and makes me feel like a complete fraud.
- trekky1700 13y agoIs it weird that I find this mesmerizing despite there being a foot of the real stuff outside my door?
- nitrogen 13y agoPerhaps the link should be http://disneyanimation.com/technology/publications/55 http://disneyanimation.com/technology/publications/55 (note the added /55) so it goes directly to the post in question, even if the page is updated (permalink was obtained by clicking the Twitter icon).
- Kerr0r 13y agoAs a CS major this fascinates me to no end, but reading the paper the physics are a bit much for my brain to handle. Can any physics-inclined people here recommend me some good books/papers so I can learn more and hopefully make more sense of this?