Return a color based on percentage. 0% is Red, and 100% is Green
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| extension UIColor { | |
| static func colorForPercent(_ percentage: Double) -> UIColor { | |
| switch percentage { | |
| case 0...0.5: | |
| return firstHalf(percentage: percentage * 2) | |
| case 0.5...1: | |
| return secondHalf(percentage: (percentage - 0.5) * 2) | |
| default: | |
| fatalError("Bad Input: percentage must satisfy 0 <= percentage <= 1") | |
| } | |
| } | |
| static fileprivate func firstHalf(percentage: Double) -> UIColor { | |
| let begin = UIColor.systemGreen.cgColor.components! | |
| let end = UIColor.systemYellow.cgColor.components! | |
| return createColor(begin: begin, end: end, percentage: percentage) | |
| } | |
| static fileprivate func secondHalf(percentage: Double) -> UIColor { | |
| let begin = UIColor.systemYellow.cgColor.components! | |
| let end = UIColor.systemRed.cgColor.components! | |
| return createColor(begin: begin, end: end, percentage: percentage) | |
| } | |
| static fileprivate func createColor(begin: [CGFloat], end: [CGFloat], percentage: Double) -> UIColor { | |
| var colorDiff = begin | |
| for i in 0 ..< 3 { | |
| colorDiff[i] = begin[i] + (end[i] - begin[i]) * CGFloat(percentage) | |
| } | |
| return UIColor(red: colorDiff[0], green: colorDiff[1], blue: colorDiff[2], alpha: 1) | |
| } | |
| } |
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