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Better Shadows With New Algorithm

December 12, 2003

Shadows are extremely important in making the graphics in 3D games and Virtual Reality applications seem natural. Soft shadows in real-time applications has largely been an unsolved problem, but now an algorithm is being introduced that will solve the problem and open many possibilities.

In his doctoral dissertation, Ulf Assarsson at the Department of Computer Engineering, Chalmers University of Technology in Göteborg, Sweden, presents a newly developed algorithm that can create shadows of a much higher quality than ever before for applications with limited calculation time.

What is this good for?
"Apart from the obvious fact that it enhances the feeling of presence in all sorts of games, the technique can be of great interest in other fields that apply Virtual Reality, such as the auto industry, architecture, and various Internet applications," he says.

Here's how it works
Sources of light that have some kind of area or volume, that is, all real sources of light, create gradual transitions on shadow edges from no shadow to full shadow. Graphics usually produce shadows with knife-sharp transitions from no-shadow to shadow - so-called "hard shadows" - since they don't require as much time to calculate.

The larger the light source is, the more diffuse the transition becomes, and it is therefore highly desirable to be able to simulate these "soft shadows" even for real-time applications that only allow some 20 milliseconds to calculate a whole image, if the goal is to produce 50 images per second.

The algorithm solves the problem by utilizing the new programming capacity offered by the latest graphics cards, which are now available even in cheap game cards.

Research on soft shadows started in the 1970s. It has come to the fore again in the last two years.

What's so special about your algorithm?
"What's unique is that it can efficiently make use of the new possibility of programming graphics cards, which are now being included in cheap game cards. This makes it extremely fast. There are a few other new algorithms, but they are either way too slow or produce low quality shadows. We are also aware of a number of up and coming inventions that will strengthen our algorithm, so we believe in its potential," says Ulf Assarsson.

The technology can also handle shadows from more advanced light sources, like the flames of a fire. The algorithm has thus far attracted the attention of players not only in the game industry like Microsoft XBox but also the film industry, where it can be used in programs for computer-generated special effects.

First in Sweden
The algorithm was introduced last summer at SIGGRAPH - the world's largest and most important computer graphics conference - and constituted one of the first two wholly full-length articles from Sweden ever chosen for the conference.

Ulf Assarsson's dissertation was directed by Associate Professor Tomas Akenine-Möller, who played a major role in the work.

Vetenskapsrådet (The Swedish Research Council)