Simulating Cloth in CG

monty writes: "Creating realistic clothing in games may not seem that difficult, but according to one of Intel's research programmers it turns out it is very difficult indeed. Intel senior technical marketing manager Dean Macri gave a presentation at the recent AGDC outlining the problems with simulating cloth, and some possible solutions. There is an online presentation (including downloadable source code and a fully configurable executable of the demonstration simulation) at The math is a bit intense, but the implications are that realistic cloth simulation remains out of reach for today's processors." Monty found it on BigKid, but I couldn't ;)

Comments

Ah...

[Electric Angst]

You see, this is just another excuse for the makers of Tomb Raider to keep Laura Croft in skimpy outfits...
"Well, we'd like to cloth her more, but it's just so hard to simulate!"
--

Realistic simulation of anything.

[onion2k]

So far noone has really managed to simulate anything within a fraction of 'realism'. The number of variables that need to be taken into consideration is absolutely horrendous. The nearest we can get without throwing Cray computing power about is a vague approximation.

But...

Isn't a vague approximation enough? Take a recent computer game as an example, say Tekken Tag Tournament or Soul Caliber on the PS2 and Dreamcast respectively. Both these games look damn good. No doubt about that. They're by no means 'realistic', far from it in fact, but who cares? The games are fun. When did gaming take to being real? Its an escape isn't it? Maybe in the future games will look like the world around us, on that day I think I'll be going back to my SNES.

Big surprise

[Chris Pimlott]

Allow me to play the cynic for a moment...

So, Intel has studied the problem and determined the answer is "We need faster processors". Is anyone surprised?

Saw this stuff in 1988!

[Speare]

When working at the chemistry department of the University of Arizona, I ended up co-sysadminning a supercomputer called the Ardent Titan. Ardent seems to have disappeared.

The Titan's focus was graphics and vector-processing. A scalar processor loads one register with one value resulting from one operation. A vector processor loads n registers with n values resulting from one operation; think "ADD AX TO EACH REGISTER IN VX[]". Four CPUs in our model, but it supported far more.

One of the sample programs was a flag hanging on a flagpole. It was a 512x512 node swatch of cloth, and it was being animated at 30fps, if I recall. You could drag your mouse to adjust a wind source. As you moved the source, the flag would flap realistically.

I had my one-processor SGI (MIPS 4000 at 100MHz) handle the same basic simulation with 64x64 nodes, a few years later. Of course, the complexity of the simulation increases geometrically with the size of the swatch of free fabric, but it's not THAT terrible.

In essence, the simulator is just an MxN array of nodes, with springs between each node horizontally, vertically and diagonally. The two diagonals can be given opposing compression limits, to emulate the thread bias of cloth. Apply forces to all nodes, and minimize the energy on each node. Take another pass to apply forces of self-collision, where one part of the fabric tries to intersect another part.

Pixar short

[RobertGraham]

The two big problems in CGI have been clothing and hair. This is why Pixar created the animated short "Geri's Game": it showed off some impressive new clothing algorithms, though they still couldn't do the hair right. However, I've seen the preview to Pixar's next movie that includes a hairy monster: the hair is amazing.

The problem with clothing is that different fabrics "hang" differently. Apparently, this is a big issue in the clothing industry and determines why clothing designers choose different fabrics for different outfits: it isn't just how the fabric looks, but how it behaves. The computer has to emulate the performance of the cloth not just in terms of how it behaves at vertices and how it stretches, but also how it behaves along with gravity. If you look in "Geri's Game", notice how the clothing folds. The designers had to emulate not just the person's body, but the structure of clothing on top of that body (until now, clothing has always been animated along with the body). Don't even get me started on the problems of textures.

In essence, the problem is very, very difficult. It is not so much a question of computing power; we are still working on how exactly to model it in the first place.

Yes...

[flieghund]

... but not necessarily in the sense you're thinking of. Allow me to explain by way of example:

When I saw the new Final Fantasy trailer, I was completely blown away. But it wasn't until I had watched the trailer a couple of times and explored the rest of the web site that I realized that one of the reasons was because the characters seemed to move so very realistically -- especially their clothes.

"Is this really an issue?" Yes, but in one of those subtle ways that is often hard to justify to the bean-counters. To me, the best special effects are the ones that don't call attention to themselves, but rather let the storyline continue. And that goes for movies and games. Since we are beginning to see more and more CG characters on the silver and game screens, any little bit towards realism is a step in the right direction.

In the attempt to escape from reality, are you really satisfied with blocky characters that jerk across the screen? Realistic cloth simulation in no way limits the possibility for "unrealistic" plot, action, character movements, etc. It only makes the characters themselves seem more realistic. If you really want to escape from "realistic" characters, go play on an old NES, or better yet an Atari. Their games have as much action, plot, and challenges as today's games -- but they don't look so realistic.