Real-time Dynamic Shadows Algorithm

Recent advances in GPU technology have produced a shift in focus for real-time rendering application, whereby improvements in image quality are sought in addition to raw polygon display performance. Rendering effects such as antialiasing, motion blur and shadow casting are becoming commonplace and will likely be considered indispensable in the near future. Recent quick improvements in graphics hardware makes the generation of new algorithms possible. New algorithms take charge of new characters of recent generation hardware will produce more realistic images in more efficient way. Shadow algorithms and visible-surface algorithms are essentially the same. Visible-surface algorithms determine which surfaces can be seen from the viewpoint; shadow algorithms determine which surfaces can be seen from the light source. Thus, the surfaces that are visible from the light source are not in shadow; those that are not visible from the light source are in shadow. When there are multiple light sources, a surface must be classified relative to each of them. A complete and famous survey on shadow algorithms is -Woo, 1990-, which has been updated by J.-M. Hasenfratz et al. 60 Shadows are useful for a variety of reasons: first, they help understand relative object placement in a 3D scene by providing visual cues. Second, they dramatically improve image realism and allow the creation of complex lighting ambiances. The emphasis is placed on a guaranteed framerate, or on the visual quality of the shadows including penumbra effects of "soft shadows". Obviously no single method can render physically correct soft shadows in real-time for any dynamic scene! However our paper aims at providing an basic study of shadow algorithms which can produce shadow in interactive way. In particular we discuss the advantages, limitations, rendering quality and cost of each algorithm. Recommendations are included based on simple characteristics of the application such as static/moving lights, single or multiple light sources, static/dynamic geometry, geometric complexity, directed or omnidirectional lights, etc. Finally we provide a new shadow algorithm which extends the linear light algorithm to simulate a round face light. We also give its OpenGL implementation detail, which should give programmer a good reference for his/her need.