map a range of values to a different range of values.

gistfile1.txt

private func mapValueToRange(value: CGFloat, largerRangeMin: CGFloat, largerRangeMax: CGFloat, targetRangeMin: CGFloat, targetRangeMax: CGFloat) -> CGFloat {

    let largerSpan = largerRangeMax - largerRangeMin
    let targetSpan = targetRangeMax - targetRangeMin
    
    // Scaled to 0-1 range.
    var scaleBy = (value - largerRangeMin) / largerSpan
    if scaleBy < 0 { scaleBy = 0 }
    if scaleBy > 1 { scaleBy = 1 }
    
    let mappedValue = targetRangeMin + (scaleBy * targetSpan)
    
    return mappedValue
}