iOS Find Color at Point Between Two Colors

Swift - 3.0 && 4.0

extension UIColor {    func toColor(_ color: UIColor, percentage: CGFloat) -> UIColor {        let percentage = max(min(percentage, 100), 0) / 100        switch percentage {        case 0: return self        case 1: return color        default:            var (r1, g1, b1, a1): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)            var (r2, g2, b2, a2): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)            guard self.getRed(&r1, green: &g1, blue: &b1, alpha: &a1) else { return self }            guard color.getRed(&r2, green: &g2, blue: &b2, alpha: &a2) else { return self }            return UIColor(red: CGFloat(r1 + (r2 - r1) * percentage),                           green: CGFloat(g1 + (g2 - g1) * percentage),                           blue: CGFloat(b1 + (b2 - b1) * percentage),                           alpha: CGFloat(a1 + (a2 - a1) * percentage))        }    }}

Usage:-

let colorRed = UIColor.redlet colorBlue = UIColor.bluelet colorOutput = colorRed.toColor(colorBlue, percentage: 50)

Result

The problem is that you're not subtracting kBottomThreshold from farenheit.

But let's simplify.

First, we want to map the input temperature to a parameter t in the range [0 ... 1]. Then, we want to map t to an output in the range [kBottomR ... kTopR], and also to an output in the range [kBottomG ... kTopG], and also to an output in the range [kBottomB ... kTopB].

UIColor *colorForDegreesFahrenheit(double fahrenheit) {    double t = (fahrenheit - kBottomThreshold) / (kTopThreshold - kBottomThreshold);    // Clamp t to the range [0 ... 1].    t = MAX(0.0, MIN(t, 1.0));    double r = kBottomR + t * (kTopR - kBottomR);    double g = kBottomG + t * (kTopG - kBottomG);    double b = kBottomB + t * (kTopB - kBottomB);    return [UIColor colorWithRed:r/255 green:g/255 blue:b/255 alpha:1];}

Thanks @ramchandra-n I implemented the extension to get the intermediate color from an array of colors by percentage

extension Array where Element: UIColor {    func intermediate(percentage: CGFloat) -> UIColor {        let percentage = Swift.max(Swift.min(percentage, 100), 0) / 100        switch percentage {        case 0: return first ?? .clear        case 1: return last ?? .clear        default:            let approxIndex = percentage / (1 / CGFloat(count - 1))            let firstIndex = Int(approxIndex.rounded(.down))            let secondIndex = Int(approxIndex.rounded(.up))            let fallbackIndex = Int(approxIndex.rounded())                        let firstColor = self[firstIndex]            let secondColor = self[secondIndex]            let fallbackColor = self[fallbackIndex]                        var (r1, g1, b1, a1): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)            var (r2, g2, b2, a2): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)            guard firstColor.getRed(&r1, green: &g1, blue: &b1, alpha: &a1) else { return fallbackColor }            guard secondColor.getRed(&r2, green: &g2, blue: &b2, alpha: &a2) else { return fallbackColor }                        let intermediatePercentage = approxIndex - CGFloat(firstIndex)            return UIColor(                red: CGFloat(r1 + (r2 - r1) * intermediatePercentage),                green: CGFloat(g1 + (g2 - g1) * intermediatePercentage),                blue: CGFloat(b1 + (b2 - b1) * intermediatePercentage),                alpha: CGFloat(a1 + (a2 - a1) * intermediatePercentage)            )        }    }}

You can use it to get an intermediate color between two or more colors:

let color = [.green, .yellow, .red].intermediate(percentage: 70)