近年來的遊戲引擎上，有許多在畫面或效能上的研究發展，往往追求的是畫面的真實感，而在畫圖希望達到全域照明的效果，也就是說除了最基本的直接照明外，如果再加上間接照明就可以讓畫面更接近真實世界，但是同時要有高品質的畫面和即時運算變成很重要的課題。
本篇論文研究一種全域照明的演算法，是Crytek公司所提出的光傳播容積演算法，它可以達到全域照明的效果、解決漫間反射的問題，因為有特殊的網格結構和球諧函數壓縮，使之可以達到即時運算。
在此會將該演算法實作出來，並且將步驟細節記錄下來，而且針對系統做不同參數的測試和比較，並且與其他方法做比較，例如光貼圖和光線追蹤，希望可以有不同的啟發。

In recent years, there are many research and development for images quality and performance about game engines. We usually want to get more photorealistic images and achieve the effect of global illumination. In addition to the basic direct lighting, we also use the indirect lighting to make the image closer to the real world. However, at the same time we have a high quality image and real-time rendering to become a very important issue.
This paper research on a kind of the global illumination algorithms from Crytek , Light Propagation Volumes. It can achieve the effect of global illumination and solve the problem about the diffuse reflection. Because it has the special volume structure and compression by spherical harmonics, it can achieve real-time rendering.
We can implement the algorithm and record the details of every step. Then, we can test the system and make the comparison of different parameters. Finally we make the different comparison with other methods, such as light maps and ray tracing for having a different inspiration.

相關研究論文
[CNS11] C Crassin, F Neyret, M Sainz : Interactive Indirect Illumination Using Voxel Cone Tracing. In Proc. of I3D, ACM (2011).
[DS05] C Dachsbacher, M Stamminger : Reflective shadow maps. In Proc. of I3D (2005).
[DK09] C Dachsbacher, J Kautz : Real-time global illumination for dynamic scenes. In ACM SIGGRAPH 2009 Courses (2009).
[JKG16] J Jendersie, D Kuri1, T Grosch ; Precomputed Illuminance Composition for Real-Time Global Illumination. In Proc. of I3D, ACM (2016).
[KD10] A Kaplanyan, C Dachsbacher : Cascaded light propagation
volumes for real-time indirect illumination. In Proc. of I3D, ACM (2010).
[THG11] S Thiedeann, N Henrich, T Grosch, S Muller : Voxel-based global
illumination. In Proc. of I3D, ACM(2011).
[Wan11] X Wang : Advanced Computer Graphics CS 563, VPL‐based Real‐Time
GI,Algorithm Light Propagation Volumes.
[WW93] J Wernecke, K Wollman : Open Inventor Mentor, 2nd Edition - Volume II,5.1.3. What is Real Time Ray-tracing?
相關研究網站
[1] Opengl-Tutorial：http://www.opengl-tutorial.org/
[2] Lighthouse3d.com：http://www.lighthouse3d.com/
[3] I3D 2010 Cascaded Light Propagation Volumes for Real Time Indirect Illumination：
http://www.crytek.com/cryengine/cryengine3/presentations/cascaded-light-propagation-volumes-for-real-time-indirect-illumination
[4] Crytek Light Propagation Volumes：http://www.crytek.com/download/Light_Propagation_Volumes.pdf
[5] Unreal Engine Light Propagation Volumes：https://docs.unrealengine.com/latest/INT/Engine/Rendering/LightingAndShadows/LightPropagationVolumes/index.html
[6] LPV(Light Propagation Volume) by unityshader：http://unityshader.hatenablog.com/entry/2014/05/10/040142
[7] Graphenix by linyizsh：http://www.cnblogs.com/linyizsh/archive/2010/02/03/1662310.html
[8] BlackHC's Adventures in the Dev World：
http://blog.blackhc.net/2010/06/rotation-of-low-order-spherical-harmonics/
相關圖片來源
圖2.1：WERNECKE J., WOLLMAN K.:Open Inventor Mentor, 2nd Edition - Volume II,5.1.3. What is Real Time Ray-tracing?
圖2.2：Global Illumination Wiki https://en.wikipedia.org/wiki/Global_illumination
圖2.3.2：Spherical harmonics Wiki https://en.wikipedia.org/wiki/Spherical_harmonics
圖2.3.2：Unity – Manual(LightProbes)
https://docs.unity3d.com/Manual/LightProbes.html
圖3.2、圖3.3.1、圖3.3.2、圖3.4.1、圖3.5：
Advanced Computer Graphics CS 563, VPL‐based Real‐Time GI, Algorithm Light Propagation Volumes