Rendering soft shadows using multilayered shadow fins.pdf

Volume 0 (1981), Number 0 pp. 1–14 Rendering Soft Shadows using Multi-layered Shadow Fins Xiao-Hua Cai 1 , Yun-Tao Jia 1 , Xi Wang 1 , Shi-Min Hu 1 and Ralph R. Martin 2 1 Tsinghua University, Beijing, China 2 Cardiff University, United Kingdom Abstract Generating soft shadows in real-time is difficult. Exact methods (such as ray tracing, and multiple light source simulation) are too slow, while approximate methods often over-estimate the umbra regions. In this paper, we introduce a new algorithm based on the shadow map method to quickly and accurately render soft shadows pro- duced by a light source. Our method builds inner and outer translucent fins on objects to represent the penumbra area inside and outside hard shadows respectively. The fins are traced into multi-layered light space maps to store illuminance adjustment to shadows. The viewing space illuminance buffer is then calculated using those maps. Finally, by blending illuminance and shading, a scene with highly accurate soft shadow effects is produced. Our method does not suffer from umbra over-estimation. Physical relations between light, objects, and shadows demonstrate the soundness of our approach. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Genera- tion: Bitmap and Frame Buffer Operations I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism: Shading, Shadowing 1. Introduction Shadows provide important cues to spatial relationships in images, improving viewers’ understanding [SUC95], so their computation has been widely studied. For interactive requirements, two widely used methods are those of shadow volumes [Cro77] and shadow maps [Wil78]. The basic ideas used by these approaches depend on point light sources only, and thus they generate hard shadows. Further work has been done to extend them to the generation of soft shadows, as we will discuss shortly. On the other hand, for soft shadow rendering, various off- line methods have