UIKit+lerp.swift

//
//  UIKit+lerp.swift
//  ha1f
//

extension CGRect {
    /// 線形補間した中間矩形を返す
    /// - parameter otherRect: 目指す先の矩形
    /// - parameter rate: 0-1の間の値。0なら自分と、1ならotherRectと同じ。
    func lerp(_ otherRect: CGRect, rate: CGFloat) -> CGRect {
        let lerp = _lerpCurried(rate)
        return CGRect(
            x: lerp(origin.x, otherRect.origin.x),
            y: lerp(origin.y, otherRect.origin.y),
            width: lerp(width, otherRect.width),
            height: lerp(height, otherRect.height)
        )
    }
}

extension UIColor {
    /// 線形補間した中間色を返す
    /// - parameter otherColor: 目指す先の色
    /// - parameter rate: 0-1の間の値。0なら自分と、1ならotherColorと同じ。
    func lerp(_ otherColor: UIColor, rate: CGFloat) -> UIColor {
        var r1: CGFloat = 0, g1: CGFloat = 0, b1: CGFloat = 0, a1: CGFloat = 0, r2: CGFloat = 0, g2: CGFloat = 0, b2: CGFloat = 0, a2: CGFloat = 0
        self.getRed(&r1, green: &g1, blue: &b1, alpha: &a1)
        otherColor.getRed(&r2, green: &g2, blue: &b2, alpha: &a2)

        let lerp = _lerpCurried(rate)
        return UIColor(
            red: lerp(r1, r2),
            green: lerp(g1, g2),
            blue: lerp(b1, b2),
            alpha: lerp(a1, a2)
        )
    }
}

extension CGFloat {
    func lerp(_ otherValue: CGFloat, rate: CGFloat) -> CGFloat {
        let lerp = _lerpCurried(rate)
        return lerp(self, otherValue)
    }
}

private func _lerpCurried(_ rate: CGFloat) -> (CGFloat, CGFloat) -> CGFloat {
    let rateInversed = 1 - rate
    return { from, to in from * rateInversed + to * rate }
}