The Research And Apply On Real-time Shadow

With the development of Computer Graphics technology and hardware, virtualenvironment is widely used in3D games, virtual manufacture, and virtual simulation, etc. Asa very important representation method in Virtual Reality, shadow can show the relativeposition of the objects clearly, so it can improve the stereoscopic impression and hierarchicaleffect of the graphics.The traditional shadow generation algorithms contain Shadow Volume algorithm andShadow Mapping algorithm. Recently, there is a lot of research in the improvement of shadowgeneration algorithms. However, these algorithms can't resolve the contradiction betweenreality and real-time rendering. After summarizing many shadow generation algorithms, thisthesis tries to improve the classic Shadow Volume algorithm in order to promote the timeefficiency. The main study on this thesis is about:A new shadow generation algorithm by ranking objects which is based on point lightsource is presented in this thesis. This algorithm can enhance Shadow Volume algorithmeffectively without reducing stereoscopic impression of the scene. The algorithm takesadvantage of the fact that in many cases, a large number of objects in the complex virtualenvironment are under the shelter of other objects. So it is unnecessary to generate shadow forthe occluded objects and make the number of objects to be calculated as less as possible.Firstly, the operations are to sort all objects in the scene by the distance between point lightsource and objects, and create sequence diagram. Secondly, Z-PASS algorithm is used todetect whether the object contained in the sequence diagram is in the Shadow Volume ofobjects which are closer to the point light source. If the object is in the Shadow Volume, thenode containing the object in the sequence diagram is removed. Otherwise the ShadowVolume algorithm is applied to generate the shadow of the object. The previous step isrepeating until each object in the sequence diagram is disposed.The algorithm presented in this thesis has the advantage of generating shadow of objectswhich occlude each other in the scene. Experimental results show that this algorithm is moreefficient than the traditional Shadow Volume algorithms in the scene where the objects occlude each other.