Photorealistic real-time rendering of spherical raindrops with hierarchical reflective and refractive maps
Synthesizing rainy images is a common challenge found in film, game engines, driving simulators, and architectural design. Simulating light transport through a raindrop's optical properties is a view-dependent problem, and large quantities of raindrops are required to produce a plausible rainy scene. Accurate methods for rendering raindrops exist but are often off-line techniques that are cost prohibitive for real-time applications. Most real-time solutions use textures to approximate the appearance of moving raindrops as streaks. These approaches produce plausible results but do not address the problem of temporal effects such as slow-motion or paused simulations. In such conditions, streak-based approximations are not suitable, and proper raindrop geometry should be considered. This paper describes a straight-forward approach for rendering raindrops in such temporal conditions. The proposed technique consists of a preprocessing stage that generates a raindrop mask and a run-time stage that renders raindrops as screen-aligned billboards. The mask's contents are adjusted on the basis of the viewpoint, viewing direction, and raindrop position. The proposed method renders millions of raindrops at real-time rates in current graphics hardware, making it suitable for applications that require high-visual quality without compromising performance. Copyright © 2011 John Wiley & Sons, Ltd.