https://community.arm.com/graphics/b/blog/posts/reflections-based-on-local-cubemaps-in-unity
https://seblagarde.wordpress.com/2012/09/29/image-based-lighting-approaches-and-parallax-corrected-cubemap/
https://seblagarde.files.wordpress.com/2012/08/parallax_corrected_cubemap-siggraph2012.pdf
https://armkeil.blob.core.windows.net/developer/Files/pdf/graphics-and-multimedia/ImplementingReflectionsinUnityUsingLocalCubemaps.pdf
camera放在camPos 生成一个local cubemap
box设置在 比如湖面的边界
Pos沿R的方向 的distance
dis= (A-O)/D
=(IntersectPosWS-Pos)/R