// Translation (from C) of utility functions Inigo Quilez
// explains in http://www.iquilezles.org/www/articles/functions/functions.htm
float almostIdentity(float x, float m, float n) {
    if(x > m) return x;

    float a = 2.*n - m;
    float b = 2.0*m - 3.0*n;
    float t = x/m;

    return (a*t + b)*t*t + n;
}

float impulse(float k, float x) {
    float h = k * x;
    return h*exp(1.0-h);
}

float cubic_pulse(float c, float w, float x) {
    x = abs(x - c);
    if(x > w) return .0;
    x /= w;
    return 1.0 - x*x*(3.0-2.0*x);
}

float parabola(float x, float k) {
    return pow(4.0*x*(1.0-x), k);
}