A function to translate a number between two different ranges

convertValue.swift

// convertValue()

// VALUE
// The number to input into the equation. 
// To consider: What will the starting and ending value be?
//
// R1MIN
// The starting input range. What is the lowest number that VALUE will have?
//
// R1MAX
// The top of the input range. What is the highest number that VALUE will have?
//
// R2MIN
// The bottom value of the target range.
//
// R2MAX
// The top value of the target range
//
// RETURN
// The number that falls somewhere inbetween r2Min and r2Max

func convertValue(value: CGFloat, r1Min: CGFloat, r1Max: CGFloat, r2Min: CGFloat, r2Max: CGFloat) -> CGFloat {
    let ratio = (r2Max - r2Min) / (r1Max - r1Min)
    return value * ratio + r2Min - r1Min * ratio
}