A Practical Guide to Thin Film and Drips Simulation.

We present a practical approach to model close-up water interaction with characters. We specifically focus on high-fidelity surface tension and adhesion effects as water sheds off skin. We show that an existing particle-in-cell (FLIP/APIC) solver can be adapted to capture small-scale water-solid interaction dynamics and discuss the role and implementation details of the relevant key components: treatment of surface tension and viscosity, enforcement of contact angle, and maintenance of contact with fast-moving collision geometry. The method allows for resolution of effects on a scale of a fraction of a millimeter and is performant enough to be able to cover a whole human body with a layer of water. We demonstrate successful use of the approach in a shot from Alita: Battle Angel.