Character splash system.(DreamWorks L.L.C. and Aardman Animations movie "Flushed Away")

Effects involving water are generally regarded as some of the most difficult to achieve. The DreamWorks/Aardman animated feature film Flushed Away (see "Flushed with Success," pg. 22) contains a wide variety of water effects, each of which posed specific challenges. Waterfalls, boat wakes, giant waves, water slides, and splashing are just some examples of water-based effects featured in the film.

Some of the most common effects in many of the movie's sequences are the splashes that result from a character's interaction with a body of water. This posed a specific challenge because of the number of shots and the variety of characters that were creating the splashes.

Tire quantity of shots that required this effect warranted the development of a character splash system that could accommodate all the scenarios quickly and efficiently. The system had to automate the process of generating splashes from a character's interaction with a water surface while still providing a large degree of control for the artists.

Completed, the system contains various tools for generating splash emissions, localizing a fluid simulation, and generating a surface from the resulting particles. It does not include a fluid dynamics simulator, but instead uses a previously developed in-house simulation tool.

In order for an animator to implement this effect efficiently, splashes from a character's water interaction were generated semi-automatically. This was done in several stages. First, the character's surfaces were converted with an evenly spaced distribution of particles using a proprietary tool. The spacing of the particles could be controlled based on how much detail was required from the character's motion. And, each particle contained a local velocity vector of the character's motion at that position.

Next, a closest point calculation was performed between each particle and the water surface with which the character was interacting. Using each particle's closest point distance, velocity, and user-controlled parameters, further calculations were performed. The user-controlled parameters could be animated over time and could also vary over the surface of the character using painted texture maps. The particles were first culled based on user-defined criteria such as a maximum distance from the water surface and a minimum velocity threshold. The positions and velocities of the remaining particles were then modified based on several computed vectors that gave the user a high degree of control over the resulting splash direction and amplitude. The resulting particles were then input into the fluid-simulation program.

Local Fluid Simulation