颜色从绿色到红色的百分比

Question

我正在尝试创建一个从绿色到红色的自定义 UIColor 取决于百分比值，但我不知道我该怎么做？

有任何想法吗？

Answer 1

如果你只是想要一个线性组合，那么沿着这些方向应该可以工作：

func mixGreenAndRed(greenAmount: Float) -> UIColor {
    return UIColor(red: (1.0 - greenAmount), green: greenAmount, blue: 0.0, alpha: 1.0)
}

那个会混合 RGB (0.5, 0.5, 0)，虽然——一种丑陋的橙色——所以你可能想要这样做，它只会调整红色和绿色之间的色调，穿过黄色，让你改变饱和度/亮度适合您的口味：

func mixGreenAndRed(greenAmount: Float) -> UIColor {
    // the hues between red and green go from 0…1/3, so we can just divide percentageGreen by 3 to mix between them
    return UIColor(hue: greenAmount / 3, saturation: 1.0, brightness: 1.0, alpha: 1.0)
}

在这两种情况下，greenAmount都应该是 0.0–1.0 之间的值，而不是 0–100。

Answer 2

您可以使用我的扩展按百分比从颜色数组中获取中间颜色

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))
        }
    }
}

用法：

let color = [.green, .red].intermediate(percentage: 50)

以及更多颜色：

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