使用光傳遞容積實作虛擬實境的即時全域照明

Abstract

電腦圖學領域的全域照明效果，包含光源及發光體對場景的直接照明，以及非發光體反射照明效果產生的間接照明，如要呈現較為擬真的畫面表現，全域照明為相當重要的效果。由於近年虛擬實境裝置崛起，以虛擬實境為平台的應用漸增，在虛擬實境中如要呈現一定品質的畫面，需加入品質不錯的全域照明效果，同時又要兼顧虛擬實境裝置的互動性。 光傳遞容積( Light Propagation Volume )及其他類似的方法，使用球諧函數近似光照貢獻度分布，其能夠用使用少量空間及在短時間內轉換貢獻度資料及球諧函數係數的性質，使得許多近年的互動式圖學內容大量使用此方法。 使用OpenGL 4.0實作光傳遞容積，以平行化完成運算來符合即時運算所需的速度，在畫面中加入全域照明效果的狀況下維持良好的互動性，並以跨平台的虛擬實境函式庫OpenVR將繪製結果呈現在虛擬實境裝置上，讓使用者有身歷其境的體驗。

This paper provides an implementation of light propagation volume using OpenGL 4.0 as graphical library. And present the result in a realistic way on virtual reality helmet by using OpenVR as virtual reality library. Virtual reality provides realistic experiences to the users by providing realistic images, 3D visual effects, and intuitive interactions. To present realistic images using computer graphic, a certain quality of global illumination effect, the combination of direct and indirect illumination effects, becomes a key factor. Since both quality and interactivity are the key requirements of virtual reality, the implementation of global illumination effect must be fast enough to complete in real-time condition. Light propagation volume(LPV) and some other ways that use spherical harmonics to approximate indirect lighting functions were introduced as real-time global illumination algorithms. LPV is widely implemented in recent interactive applications because of the decent effect and interactivity it provided.