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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