By Mark Ward
Technology correspondent, BBC News website, San Diego
Honey features prominently in the forthcoming Bee Movie
Digital depictions of food formed a theme at the Siggraph show as animators and academics talked about the challenges of capturing the various qualities of the stuff we eat.
Allen Ruilova from animation studio Dreamworks has become the world expert on virtual honey while working on the forthcoming Bee Movie due for release in November 2007.
As its title implies the film is about a bee, and honey forms a significant part of the setting for it.
Initially, said Mr Ruilova, he spent time simply filming honey to see how it looked and reacted when being poured or pooling on a surface.
"We took a lot of reference," he said.
This revealed, he said, that honey has a very particular dynamic when it is flowing that is very different to the flows seen in thinner liquids.
"The flow was a big challenge," he said. "Honey tends to retain its structure, it tends to keep that but eventually transitions to something more liquidy-like."
Mr Ruilova initially thought that turning up the viscosity controls on Dreamworks in-house fluid animating system would meet this challenge.
Eggs caused particular headaches for the animators of Ratatouille
Unfortunately, he said, that did not produce realistic virtual honey.
The solution to getting honey-like movement was adding separate elastic forces to the fluid simulation.
This meant that the virtual honey, just like its real counterpart, retained some of its structure as it flowed. But, once a set stiffness value was exceeded, the virtual flowed more like a liquid.
Also tricky, said Mr Ruilova, was getting the look of the digital honey right.
Reference footage of honey showed how it reflected and absorbed light and this was used to modify the software that depicts how light travels through the fluid.
The finishing touch was to add bubbles to the flow of the honey to give viewers more cues about how it is moving.
"Bubbles tell you more about the motion than surface movement," he said.
More challenges were faced by animators at Pixar who worked on the studio's Ratatouille movie about a rat that wants to be a chef.
In a paper presented to the conference, Tolga Goktekin and colleagues from Pixar revealed how they simulated materials such as egg whites and yolks, dough, sauces and soups for the film.
The animators faced several problems because, in many cases, the foodstuffs were deformed by being rolled, cracked or stirred during action sequences.
Eggs and doughs were simulated by giving them an internal structure of virtual springs that could be convincingly deformed.
Also at the show, the University of California, San Diego, showed off the work it was doing to create digital milk.
The computer model of the fat and protein content of milk was developed by Professor Henrik Jensen, an Oscar-winning computer graphics researcher in the computer science department at UC San Diego.
Professor Jensen said milk presented a particular problem for simulators because of the way that the substances of which it is composed absorb and reflect light. Often, animators had to shoot a lot of footage of milk and compare with the eye how their virtual creation matched up to the real thing.
By contrast the model developed by Professor Jensen and his colleagues can automatically simulate milk samples even if they have very different concentrations of fat and protein.
The use of the model was not limited to just depicting milk in films or animated works, said Professor Jensen.
As well, he said, it can be a diagnostic tool to work out the fat and protein content of a glass of milk from a digital image.
"Putting the model in reverse, grocery stores could identify spoiled meats, contaminants or other food safety issues - if a particular food problem consistently and detectable changed the light scattering properties of the food," he said.