swift 图片裁剪

Swift:
需求:图片等比例缩放,截取上部,不失真
代码如下:

extension UIImage {
    //将图片缩放成指定尺寸（多余部分自动删除）
    func scaled(to newSize: CGSize) -> UIImage {
        //计算比例
        let aspectWidth  = newSize.width/size.width
        let aspectHeight = newSize.height/size.height
        let aspectRatio = max(aspectWidth, aspectHeight)
        
        //图片绘制区域
        var scaledImageRect = CGRect.zero
        scaledImageRect.size.width  = size.width * aspectRatio
        scaledImageRect.size.height = size.height * aspectRatio
        scaledImageRect.origin.x    = 0
        scaledImageRect.origin.y    = 0
        
        //绘制并获取最终图片
        UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0)//图片不失真
        draw(in: scaledImageRect)
        let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        return scaledImage!
    }
}