MTLTexture轉成UIimage

使用Metal處理完圖像想要獲取成UIimage，然后保存，Metal處理完的圖片大小特別大，需要縮小之后再保存，如果MTLTexture是metalView.currentDrawable?.texture 獲取的，需要將metalView.framebufferOnly 設置為false

//點擊事件保存圖片
    @objc func getMetalImage(btn:UIButton){
        if let texture = metalView.currentDrawable?.texture {
            metalView.removeFromSuperview()
            let imageview1 = UIImageView(frame: CGRect(x: 0, y: 100, width: 414, height: 500))
            imageview1.image = mtlTextureToUIImage(texture: texture, wScale: imageRender.imageScale.0, hScale: imageRender.imageScale.1)
            imageview1.backgroundColor = .green
            imageview1.contentMode = .scaleAspectFit
            view.addSubview(imageview1)
        }
        
    }
    
    ///MTLTexture轉成UIimage，
    /// - Parameters:
    ///   - texture: texture ，傳入的值如果是metalView.currentDrawable?.texture，需設置metalView.framebufferOnly = false
    ///   - wScale: 寬度方向的有效圖像比例，用於剪切圖像
    ///   - hScale: 高度方向的有效圖像比例
    /// - Returns: 返回UIimage
    func mtlTextureToUIImage(texture:MTLTexture,wScale:CGFloat,hScale:CGFloat) -> UIImage? {
        let ciimage = CIImage(mtlTexture: texture, options: nil)
        //            let image = UIImage(ciImage: ciimage!)//直接獲取圖片太大且有空白
        //剪切圖片
        let croppedCiImage = ciimage?.cropped(to: CGRect(x: CGFloat(texture.width)/2 * (1 - wScale), y: CGFloat(texture.height)/2 * (1 - hScale), width: CGFloat(texture.width) * wScale, height: CGFloat(texture.height) * hScale))
        metalView.removeFromSuperview()
        
        var uiimage12 = UIImage(ciImage: croppedCiImage!)
        let home = NSHomeDirectory() + "/Documents/image121.png"
        //存取一下，否則uiimage12.cgImage為nil
        try? uiimage12.pngData()?.write(to: URL(fileURLWithPath: home))
        uiimage12 = UIImage(contentsOfFile: home)!
        
        //圖像寬高比
        let aspectRatio = uiimage12.size.width/uiimage12.size.height
        //給定一個合適的大小尺寸，我取得是iPhone8Plus寬414
        let size = CGSize(width: 414, height: 414 / aspectRatio)
        
        try? FileManager().removeItem(at: URL(string: home)!)
        
        //繪制圖片，因為圖片太大重新繪制（縮小）
        UIGraphicsBeginImageContext(size)
        //獲取context
        let context = UIGraphicsGetCurrentContext()!
        ///繪制
        context.draw(uiimage12.cgImage!, in: CGRect(x:0 , y: 0, width: size.width, height: size.height))
        //翻轉
        context.translateBy(x: 0, y: -size.height)
        context.scaleBy(x: 1, y: -1)
        //獲取繪制的圖像
        let image1 = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        return image1
    }