使用WebXR Device API實作基於球諧函數的擴增實境光照估計模型

Abstract

計算機圖學的領域中，基於物理的繪圖（Physically Based Rendering）模擬真實世界的光照傳遞，依物體的表面材質來計算虛擬物件接收到的光線影響。儘管現今電腦運算單元的計算效能持續升級，但模擬真實的物理光照，依舊需要耗費大量時間與運算力。如今許多應用是在手機裝置上實現，行動裝置的效能更難與電腦規格匹敵，品質與速度兩者間往往必須做出一定程度的取捨。擴增實境裡，使用者需要在現實世界的場景中，與電腦生成的虛擬物件互動，與電玩遊戲一樣，需要即時的互動回饋。過去擴增實境多以手機應用程式為主流的體驗；近年來，越來越多開發者探索透過網頁實現擴增實境與虛擬實境，本論文使用由全球資訊網協會發布，目前仍處於實驗性階段的WebXR Device API探索WebAR世界。論文結合了球諧函數與基於網頁的擴增實境，在WebAR平台上以球諧函數計算擴增實境中的光照估計，並透過實作探討WebAR平台的優勢與可能的侷限性，以及未來擴增實境在網頁上的發展潛能。

In computer graphics, physically based rendering is a set of techniques to model real-world lights and evaluate how environment light affects surface materials of virtual objects in the scene. Despite the development of computer hardware over the decades, simulating lighting physically is still a challenging task which requires lots of time to compute. Moreover, most of applications are implemented on mobile devices nowadays. However, the computing power of mobile devices cannot catch up with desktop computers. Developers have to strike a balance between quality and speed.In augmented reality(AR), a user interacts with computer-generated virtual objects in a real-world view. Like computer games, AR is required to provide instant feedback to a user. In the past, app-based AR is the most common way to enter AR world. Nevertheless, there is an increasing need to implement VR and AR on immersive web.The research is aimed to combine spherical harmonics and latest WebXR Device API announced by W3C to achieve light estimation on immersive web. WebXR Device API, an experimental WebXR development tool, is adopted to explore the WebAR experience. Additionally, the advantage, restrictions and future potential of WebAR platform are also discussed.