Making Animated Fluids Look More Realistic

brunascle writes "Technology Review has an article about recent advances in animated fluid dynamics made by Mathieu Desbrun, a computer science professor at Caltech. 'He and his team are developing an entirely new approach to fluid motion, based on new mathematics called discrete differential geometry, that use equations designed specifically to be solved by computers rather than people.' Desbrun explains that the currently in-use equations for animating fluid dynamics were not developed with computers in mind, and were simply reworkings of older equations. He claims that his new equations use about the same amount of computer resources, but with much better results. The article includes a 5 minute (flash) video demonstrating various results using his equations, ending with 2 fascinating and vivid displays: the first of a snowglobe, and the second of a cloud of smoke filling a volume in the shape of a bunny."

Comments

Fluids in games

[PIPBoy3000]

For us gamers, the cool application is clearly fluids in games. Currently water is a flat plane with a bump map, or possibly an animated plane that is extremely simple. Modern game engines are trying to have some simple fluid dynamics, but it's extremely CPU intensive.

The article talks about breaking problems into smaller pieces, which means that it should work well with multi-core processors. Probably you'll first see "cosmetic" fluid dynamics, which don't affect gameplay, but still look pretty cool. Imagine characters splashing in water, setting off waves, creatures vaporizing into a puddle, and so on. Should be cool.

Re:Fluids in games

[Xzzy]

We're still a long, long way from doing this in real time.

In a general sense, computer graphics follow a pattern where someone researches a new method, the ray tracing community adopts it into their tools, refine the technology, then some sharp thinking programmer hacks up a way to approximate the effect so it can be done in real time in a game. Bump mapping, for example, was first introduced in 1996. We didn't start seeing it heavily used in games until around 2004, and it was a combination of advancing computing power and optimization.

Not that I'm an expert, but based on this I'd guess we're at least 8 years away from having fluid simulation in whatever the FPS of the month is.

It's not clear

[GuyMannDude]

Remember that just because a simulated fluid flow "looks" more accurate, that doesn't mean that it is. The article isn't very technical at all so it's difficult to tell what's going on here. But the way it is phrased leads me to believe that they are solving new equations rather than using new techniques to solve the well-known traditional equations (e.g., Navier-Stokes, Euler, vorticity evolution equation, etc.). The result may be that the new equations are less accurate in a point-wise sense but the resulting gross observable features of the flow may look more natural. Your eye can't tell the difference between errors O(h) and O(h^2) where h is the grid spacing, but it can certainly tell if artificial viscosity from the numerical scheme causes obvious features of the flow, such as shock waves or density discontinuities, to diffuse with time.

The applications you list require that the estimates of velocity, pressure, etc. come out accurately, and not that the resulting animated fluid flow passes the "looks plausible" test. When you're doing computational fluid dynamics solely for graphics, however, the pointwise accuracy doesn't mean squat; you want something that looks nice. I'm guessing that they've come up with a method that is optimized to make pretty movies at the expense of true numeric accuracy of the flowfield. But, again, the article is worded so generically, it's hard to tell what's going on.

GMD