====== Perlin Noise ======
  * [[https://en.wikipedia.org/wiki/Perlin_noise|wiki]] 
  * [[http://zh.wikipedia.org/zh-sg/Perlin%E5%99%AA%E5%A3%B0|中文wiki]]
  * [[http://mrl.nyu.edu/~perlin/|算法发明者Ken Perlin的主页]]  [[http://mrl.nyu.edu/~perlin/noise/| JAVA REFERENCE IMPLEMENTATION OF IMPROVED NOISE]]
  * [[http://www.cnblogs.com/babyrender/archive/2009/02/05/1320689.html|在图形学材质上的应用]]
  * [[http://freespace.virgin.net/hugo.elias/models/m_perlin.htm|这个介绍不错]]
  * [[https://solarianprogrammer.com/2012/07/18/perlin-noise-cpp-11/|Perlin noise in c++11]]
===== 相关 =====
  * Smoothstep: [[wp>Smoothstep]] $$ \operatorname{smoothstep}(t) = 3t^2 - 2t^3 $$  $$ \operatorname{smootherstep}(t) = 6t^5 - 15t^4 + 10t^3 $$