easeInOutBack constant

A cubic animation curve that starts slowly, speeds up, and then ends slowly. This curve can be imagined as Curves.easeInBack as the first half, and Curves.easeOutBack as the second.

Since two curves are used as a basis for this curve, the resulting animation will overshoot its bounds twice before reaching its end - first by exceeding its lower bound, then exceeding its upper bound and finally descending to its final position.

Derived from Robert Penner’s easing functions.