Returns a value from 0 to 1 that represents a parameter’s proportional distance between a minimum and maximum value. This function lets you increase an attribute such as Opacity from 0 to 1 linearly over a time range.
float linstep(float start, float end, float parameter)
start and end specifies the minimum and maximum values.
parameter is the value you want to use to generate the proportional number.
If parameter is less than start, linstep returns 0.
If parameter is greater than end, linstep returns 1.