Direct raytracing of a closed-form fluid meniscus

Abstract

We present a direct raytracing method for implicitly described fluid surfaces that takes into account the effects of capillary solid coupling at the boundaries. The method is independent of the underlying fluid simulation method and solely based on distance fields. We make use of the closed-form solution of the meniscus shape at the fluid interface to achieve the effect of surface tension exerted by the solid object. The shape of the liquid at these boundaries is influenced by various physical properties such as the force of gravity and the affinity between the liquid and the solid material. We generate contact angles at the boundaries without the need for computationally intensive small-scale simulation. At render time, we combine the closed-form solution for a small-scale effect with the numerical solution of a large-scale simulation. Our method is applicable for any implicit representation of the fluid surface and does not require an explicit extraction of the surface geometry. Therefore, it is especially useful for particle-based simulations. Furthermore, the solution is guaranteed to yield the correct contact angle and, for certain scenarios, it delivers the entirely correct solution throughout the interface; even in general scenarios, it yields plausible results. As for an example, we implemented and tested the proposed method in the setting of a smoothed particle hydrodynamics (SPH) fluid simulation.