UIImage 的扩展方法记录 crop resize scaleToFitAtCenter

修改UIImage的size大小，生成新的UIImage

extension UIImage {
    func crop(_ rect: CGRect) -> UIImage? {
        var newRect = rect
        newRect.origin.x *= scale
        newRect.origin.y *= scale
        newRect.size.width *= scale
        newRect.size.height *= scale
        guard let imageRef = self.cgImage?.cropping(to: newRect) else { return nil }
        return UIImage(cgImage: imageRef, scale: scale, orientation: imageOrientation)
    }
    
    func resize(_ size: CGSize) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.main.scale)
        self.draw(in: CGRect(origin: .zero, size: size))
        let resizedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return resizedImage
    }
    
    func scaleToFitAtCenter(size: CGSize) -> UIImage? {
        let scaleW_H = size.width / size.height
        let selfScaleW_H = self.size.width / self.size.height
        
        if selfScaleW_H > scaleW_H {
            let w = self.size.height * scaleW_H
            let h = self.size.height
            let x = (self.size.width - w) / 2.0
            let y: CGFloat = 0
            return self.crop(CGRect(x: x, y: y, width: w, height: h))?.resize(size)
        } else {
            let w = self.size.width
            let h = self.size.width / scaleW_H
            let x: CGFloat = 0
            let y = (self.size.height - h) / 2.0
            return self.crop(CGRect(x: x, y: y, width: w, height: h))?.resize(size)
        }
    }
}