Returns a value from 0 to 1 that represents a parameter’s proportional distance between a minimum and maximum value. The smoothstep function lets you increase an attribute such as Opacity from 0 to 1 gradually, but nonlinearly, over a time range.
The smoothstep function works like the linstep function, except it increases values more quickly near the middle values between the minimum and maximum value. The function uses hermite interpolation between minimum and maximum values.
CloudShape.opacity = smoothstep(0,5,age);
This increases the Opacity attribute of CloudShape in steps from 0 to 1 for the first 5 seconds of the object’s age. This makes the object fade in from transparent to opaque. The fade in and fade out of the opacity occurs more quickly around 2.5, the midpoint between 0 and 5.