Artist-Directable Real-Time Rain Rendering in City Environments

Abstract

Photorealistic rain greatly enhances the scenes of outdoor reality, with applications including computer games and motion pictures. Rain is a complex atmospheric natural phenomenon. It consists of numerous interacting visual effects. We present a comprehensive real-time system for the realistic rendering of rain effects in complex environments in real-time. Our system is intuitive, flexible and provides a high degree of artistic control for achieving the desired look. We describe a number of novel GPU-based algorithms for rendering the individual components of rain effects, such as a hybrid system of an image-space approach for rainfall and the particle-based effects for dripping raindrops and splashes; water surface simulation for ripples; animation and rendering of water droplets trickling down on transparent glass panes; view-dependent warped reflections and a number of additional effects. All our techniques respond dynamically and correctly to the environment lighting and viewpoint changes as well as the atmospheric illumination due to lightning. Our effects can be rendered at interactive rates on consumer graphics hardware and can be easily integrated into existing game and interactive application pipelines or offline rendering.