2 Additional SmoothStep variants

[torridgristle]

Inigo Quilez's Improved Texture Interpolation x * x * x * (x * (x * 6.0 - 15.0) + 10.0)
http://www.iquilezles.org/www/articles/texture/texture.htm

aliaspider's SmoothestStep x * x * x * x * (x * (x * (-20.0 * x + 70.0) - 84.0) + 35.0)
https://github.com/libretro/glsl-shaders/blob/master/retro/shaders/smootheststep.glsl

[torridgristle]

Edit isn't working.

The math attributed to Inigo Quilez is actually Ken Perlin's work and SmoothestStep which was attributed to aliaspider was an example from the Smoothstep Wikipedia page. https://en.wikipedia.org/wiki/Smoothstep