https://github.com/lkewis/UnityKinectBoxing/blob/master/Assets/Script/CameraScript.js
https://forum.unity.com/threads/vr-cave-projection.76051/
https://gamedev.stackexchange.com/questions/35984/off-center-projection
https://en.wikibooks.org/wiki/Cg_Programming/Unity/Projection_for_Virtual_Reality
http://pages.cs.wisc.edu/~kponto/publications/uni-cave-unity3d.pdf
https://forum.unity.com/threads/cave-display-configuration.371689/
https://forum.unity.com/threads/virtual-reality-support-for-stereo-displays.489151/
https://forum.unity.com/threads/custom-projection-matrix-so-close-major-help-needed.83321/
https://www.theseus.fi/bitstream/handle/10024/76041/Nivala_Timo.pdf
https://www.reddit.com/r/Unity3D/comments/3upfqf/need_your_help_creating_a_frustum/
https://www.reddit.com/r/Unity3D/comments/3upfqf/need_your_help_creating_a_frustum/
https://assetstore.unity.com/packages/templates/ict-vr-cave-multiscreen-configuration-project-17080
unity default projection matrix is symmetric:
