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Swift - 给图片添加图片水印（图片上绘制另一张图，并可设透明度）

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07/25
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我前面写了篇文章讲解如何给图片添加文字水印，而如果想要添加图片类型的水印也很简单，只要把原来代码里添加文字的部分改成图片即可。
1，效果图如下：
（在图片左上角添加了一个半透明的logo图片）
2，为方便使用，我们通过扩展UIImage类来实现添加图片水印功能
（水印图片透明度，位置，边距都可以设置）
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//--- UIImageExtension.swift ---
extension UIImage{
     
    //水印位置枚举
    enum WaterMarkCorner{
        case TopLeft
        case TopRight
        case BottomLeft
        case BottomRight
    }
     
    //添加图片水印方法
    func waterMarkedImage(waterMarkImage:UIImage, corner:WaterMarkCorner = .BottomRight,
        margin:CGPoint = CGPoint(x: 20, y: 20), alpha:CGFloat = 1) -> UIImage{
             
            var markFrame = CGRectMake(0, 0, waterMarkImage.size.width, waterMarkImage.size.height)
            let imageSize = self.size
             
            switch corner{
            case .TopLeft:
                markFrame.origin = margin
            case .TopRight:
                markFrame.origin = CGPoint(x: imageSize.width - waterMarkImage.size.width - margin.x,
                    y: margin.y)
            case .BottomLeft:
                markFrame.origin = CGPoint(x: margin.x,
                    y: imageSize.height - waterMarkImage.size.height - margin.y)
            case .BottomRight:
                markFrame.origin = CGPoint(x: imageSize.width - waterMarkImage.size.width - margin.x,
                    y: imageSize.height - waterMarkImage.size.height - margin.y)
            }
             
            // 开始给图片添加图片
            UIGraphicsBeginImageContext(imageSize)
            self.drawInRect(CGRectMake(0, 0, imageSize.width, imageSize.height))
            waterMarkImage.drawInRect(markFrame, blendMode: .Normal, alpha: alpha)
            let waterMarkedImage = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
             
            return waterMarkedImage
    }
}

3，使用样例

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import UIKit
 
class ViewController: UIViewController {
 
    @IBOutlet weak var imageView: UIImageView!
     
    override func viewDidLoad() {
        super.viewDidLoad()       
         
        //给图片添加水印
        imageView.image = UIImage(named:"bg")?
            .waterMarkedImage(UIImage(named: "logo7")!,corner: .TopLeft,
                margin: CGPoint(x: 20, y: 20), alpha:1)
    }
 
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}