非對稱圓錐映射貼圖

Abstract

這篇論文介紹一種更有效率且精準的方法來計算視線(view ray)與位移圖(displacement map)的交點，稱為非對稱圓錐映射貼圖(Anisotropic Cone Mapping)，簡稱ACM。經由前置處理(pre-processing)，我們在每個位移圖的texel 上方都去找一個非對稱圓錐的體積空間來當成是可以略過的空乏區。使用這樣的資訊可以讓一條視線(射線)快速地跳過空乏區並且可以很快的就收斂到與位移圖的交點。這樣的做法可以允許視線從極端近距離與傾斜的角度看進去而不會產生可察覺的瑕疵。我們更進一步提出一個可適應性的階層架構方法來加速前置處理的時間。這個方法比傳統的方法快上6 到11 倍，因此使得ACM 可以應用在繪製即時的動態位移圖，也適合很多的即時3D 應用像電玩或者是一些互動的模擬。由於它耗用的記憶體成本很低而且有很好的效能表現無論是繪圖的品質或速度都可以兼顧。

This paper presents Anisotropic Cone Mapping (ACM), a more efficient and accurate way for calculating intersections with displacement maps. During preprocessing, for each texel of the displacement map, an asymmetric cone is calculated as the bounding volume for the empty space above that texel. By using this information, a ray can fast skip empty space and quickly converge to its intersection with the displacement map. Thus, it allows extreme closeup and very steep angle views without noticeable artifacts. Furthermore, we propose a hierarchical adaptive method to speed up the preprocessing of ACM. The proposed method is around 6 to 11 times faster than conventional methods, thus allowing application of ACM to render dynamic displacement maps in real-time. Its suited for many real-time 3D applications like games or interactive simulations because of their low memory cost and good performance in both rendering quality and speed.