Animation of Water Droplets on a Glass Plate

This paper proposes a method for generating an animation of water droplets and their streams on a glass plate, such as a windowpane or windshield, taking into account the dynamics between fluid and solid. Water droplets run down an inclined glass plate if their masses are greater than a static critical weight. The streams from the droplets do not run straight down the glass plate but meander and some amount of water remains behind the flow due to the nature of the wetting phenomenon. Therefore, the mass of the water droplet decreases. When the mass becomes smaller than a dynamic critical weight, the flow stops. In this paper, a discrete model of a glass plate is developed to simulate the streams from the water droplets as described above. The glass plate is divided into small meshes. For rendering scenes through a glass plate upon which there are water droplets, we also develop a high-speed rendering method taking into account reflection and refraction of light. Instead of calculating the intersections between the ray and the objects, one of the most time-consuming processes in ray tracing, the proposed method determines pixel colors by using the intersection between the ray and a cuboid onto which objects in a scene are projected. Animations of rain droplets on a pane or windshield demonstrate the usefulness of the proposed method.