quadratic-ease-in-out.js

// Modeled after the piecewise quadratic
// y = (1/2)((2x)^2)             ; [0, 0.5)
// y = -(1/2)((2x-1)*(2x-3) - 1) ; [0.5, 1]
function quadraticEaseInOut (p) {
    if(p < 0.5) {
        return 2 * p * p;
    } else {
        return (-2 * p * p) + (4 * p) - 1;
    }
}