ios - 无法快速使用 CGImageCreateWithImageInRect 裁剪触摸位置

Question

我试图在触摸位置复制背景图像的一部分，然后在与裁剪部分相同的位置添加 subview 。如果我做的正确，两张图片会排成一行，你无法分辨出那里有两个 UIImageView，但它最终看起来像下面的图片。为什么这没有对齐，为什么新图像放大了一点？

更新:我的 ImageView 与主视图大小相同，图像模式是 aspect fit，所以图像上方和下方的白色仍然是 imageview 的一部分。

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
    let touch = touches.first!.locationInView(view)
    let rect = CGRect(origin: touch, size: CGSize(width: 90, height: 90))

    let imageRef = CGImageCreateWithImageInRect(mainImageView.image!.CGImage, rect)

    if imageRef != nil {
        let newImage = UIImage(CGImage: imageRef!)

                let bgImage = UIImageView(image: newImage)
                bgImage.center = touch
                self.view.addSubview(bgImage)
                self.view.bringSubviewToFront(bgImage)
            }
}

接触前:

触后:

Answer 1

我终于明白了:

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {

    let touch = touches.first!.locationInView(view)

    UIGraphicsBeginImageContext(mainImageView.bounds.size)
    UIApplication.sharedApplication().keyWindow!.layer.renderInContext(UIGraphicsGetCurrentContext()!)
    let screenshot = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    let crop = CGRectMake(touch.x - 45, touch.y - 45, 90, 90)
    let imageRef = CGImageCreateWithImageInRect(screenshot.CGImage, crop)

    if imageRef != nil {
        let newImage: UIImage = UIImage(CGImage: imageRef!, scale: mainImageView.image!.scale, orientation: mainImageView.image!.imageOrientation)

                let bgImage = UIImageView(image: newImage)
                bgImage.center = touch
                self.view.addSubview(bgImage)
                self.view.bringSubviewToFront(bgImage)
            }
        }
    }

}