[GLSL] Gain

 

http://www.iquilezles.org/www/articles/functions/functions.htm

Inigo Quilez

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Remapping the unit interval into the unit interval by expanding the sides and compressing the center, and keeping 1/2 mapped to 1/2, that can be done with the gain() function. This was a common function in RSL tutorials (the Renderman Shading Language). k=1 is the identity curve, k<1 produces the classic gain() shape, and k>1 produces "s" shaped curces. The curves are symmetric (and inverse) for k=a and k=1/a.

classic gain() shape

float gain(float x, float k){
    float a = 0.5*pow(2.0*((x<0.5)?x:1.0-x), k);
    return (x<0.5)?a:1.0-a;
}