Percent = function (value, min, max, upperMax)
{
    if (max === undefined) { max = min + 1; }

    var percentage = (value - min) / (max - min);

    if (percentage > 1)
    {
        if (upperMax !== undefined)
        {
            percentage = ((upperMax - value)) / (upperMax - max);

            if (percentage < 0)
            {
                percentage = 0;
            }
        }
        else
        {
            percentage = 1;
        }
    }
    else if (percentage < 0)
    {
        percentage = 0;
    }

    return percentage;
}
Work out what percentage `value` is of the range between `min` and `max`.
If `max` isn't given then it will return the percentage of `value` to `min`.

You can optionally specify an `upperMax` value, which is a mid-way point in the range that represents 100%, after which the % starts to go down to zero again.

@function Phaser.Math.Percent
@since 3.0.0

@param {number} value - The value to determine the percentage of.
@param {number} min - The minimum value.
@param {number} [max] - The maximum value.
@param {number} [upperMax] - The mid-way point in the range that represents 100%.

@return {number} A value between 0 and 1 representing the percentage.