Physically based animation

Physically based animation is an area of interest within computer graphics concerned with the simulation of physically plausible behaviors at interactive rates. Advances in physically based animation are often motivated by the need to include complex, physically inspired behaviors in video games, interactive simulations, and movies. Although off-line simulation methods exist to solve most all of the problems studied in physically-based animation, these methods are intended for applications that necessitate physical accuracy and slow, detailed computations. In contrast to methods common in offline simulation, techniques in physically based animation are concerned with physical plausibility, numerical stability, and visual appeal over physical accuracy. Physically based animation is often limited to loose approximations of physical behaviors because of the strict time constraints imposed by interactive applications. The target frame rate for interactive applications such as games and simulations is often 25-60 hertz, with only a small fraction of the time allotted to an individual frame remaining for physical simulation. Simplified models of physical behaviors are generally preferred if they are more efficient, easier to accelerate (through pre-computation, clever data structures, or SIMD/GPGPU), or satisfy desirable mathematical properties (such as unconditional stability or volume conservation when a soft body undergoes deformation). Fine details are not important when the overriding goal of a visualization is aesthetic appeal or the maintenance of player immersion since these details are often difficult for humans to notice or are otherwise impossible to distinguish at human scales.

Physically based animation is now common in movies and video games, and many techniques were pioneered during the development of early special effects scenes and game engines. Star Trek II: The Wrath of Khan famously used particle systems in the Genesis explosion scene to create the visual effect of a flaming shockwave engulfing a planet. Despite being released before physics engines were a common feature in games, System Shock incorporated rigid body physics in its engine and was widely considered innovative for this feature and the novel sense of interaction it afforded players. Valve later developed Half-Life and used rigid body physics to create environmental puzzles for the player, such as obstacles that could not be reached without stacking boxes. Half-Life 2 featured a more advanced physics engine that incorporated constrained systems such as pulleys or levers with more environmental puzzles to showcase these features. Physics engines are now much more common in games, and their frequent appearance has motivated research in physically based animation by companies such as Nvidia.

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