動態環境的陰影計算

Abstract

陰影效果在互動的環境中，相當的重要．它可以使人對物體間的相對位置 有更好的了解，而更為融入虛擬的情境中．本論文嘗試在一個由多邊形組 成的場景中，產生物體的陰影，並快速的反應物體移動後，陰影的變化， 以支援動態的需求．[CS95]中，利用二元空間切割法(BSP)，加上多邊形 的陰影空間(Shadow Volume)的 BSP tree 表示法，進行陰影的計算，並 利用塊速的 BSP tree 的重組，支援動態上的應用．我們修改[CS95]的作 法，以面向光源的多邊形群組作為陰影計算的基本單位，以期能減少 BSP tree 的節點個數，減少切割，進而增進陰影產生的效率以及動態重組 BSP tree 的效率．根據我們的測試，若面向光源的多邊形群組為 convex ，我們的方法有不錯的效率；然而若面向光源的多邊形群組為 concave， 則會影響效率，文中將會對此一情況作一討論． The shadow effect plays a very important role in interactive environmentsin which the perception of the spatial relations between objects can beenhanced. In this thesis, we attempt to generate shadows for both staticand dynamic polygonal scenes. A shadow computation algorithm based on theBSP tree representation of shadow volumes for polygons was proposed in[CS95]. We extend the method to compute shadows; but using the shadow volume generated by a connected set of polygons that are front-facing withrespect to the light source, which we call Light Facing Components ( LFCs ). We hope that the number of tree nodes and the number of shadow fragmentscan be reduced and hence the efficiency of shadow generation for static anddynamic scenes can be improved. According to our experiments, considerableefficiency speed-up are obtained for scenes with convex LFCs, but not forscenes with concave LFCs. Discussions on how to overcome the problems inducedby the concave LFCs will be addressed .