== PBRT ==

 * PBRT book - http://www.pbrt.org/
 * https://github.com/mmp/pbrt-v3/ -- PBRT book code v3
 * https://github.com/mmp/pbrt-v2/ -- PBRT book code v2

 * pbr intro http://www.codinglabs.net/article_physically_based_rendering.aspx
 * pbr-cook-torrance http://www.codinglabs.net/article_physically_based_rendering_cook_torrance.aspx