CGContext在UIImage错误的部分绘制

Question

我正在尝试开发一个应用程序，允许用户通过拖动手指（例如Snapchat）来拍照并在照片上绘画。我非常接近要使该功能正常工作，但是我遇到了一个问题，我认为这与UIImageView的contentMode某种程度上有关，这弄乱了我的行的位置。在屏幕边缘最明显。如果我使用scaleAspectFill并尝试用手指跟踪屏幕的边缘，则会看到以下内容：

如您所见，左侧和底部的线不在屏幕上。如果我使用scaleAspectFit并执行相同的操作，则结果如下：

在这种情况下，左侧和底部正确，而右侧/顶部不正确。我的绘图代码如下：

var lastPoint:CGPoint!
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesBegan(touches, with: event)
    if self.capturedImageView.isHidden == false && self.isDrawing {
        self.lastPoint = CGPoint(x: touches.first!.location(in: self.capturedImageView).x, y: touches.first!.location(in: self.capturedImageView).y)
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesMoved(touches, with: event)
    if (self.capturedImageView.isHidden == false && lastPoint != nil && self.isDrawing) {
        self.capturedImageView.image = self.drawLine(onImage: self.capturedImageView.image!, fromPoint: CGPoint(x: touches.first!.location(in: self.capturedImageView).x, y: touches.first!.location(in: self.capturedImageView).y), toPoint: lastPoint)
    }
        self.lastPoint = CGPoint(x: touches.first!.location(in: self.capturedImageView).x, y: touches.first!.location(in: self.capturedImageView).y)
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesEnded(touches, with: event)
    self.lastPoint = nil
}

//drawLine creates a new UIImage with the desired line drawn on it, 
//which I then use to replace capturedImageView.image
func drawLine(onImage: UIImage, fromPoint: CGPoint, toPoint: CGPoint) -> UIImage {

    // Create a context of the starting image size and set it as the current one
    UIGraphicsBeginImageContext(onImage.size)

    // Draw the starting image in the current context as background
    onImage.draw(at: CGPoint.zero)

    // Get the current context
    let context = UIGraphicsGetCurrentContext()!

    // Draw a red line
    context.setLineWidth(5.0)
    context.setStrokeColor(UIColor.red.cgColor)
    context.move(to: fromPoint)
    context.addLine(to: toPoint)
    context.strokePath()

    // Save the context as a new UIImage
    let myImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    // Return modified image
    return myImage!
}

我认为我做错了，因为UIImageView本身的触摸坐标与UIImageView图像内的坐标不同。不过，我真的很困惑如何解决此问题。如何获取触摸的位置而不是CapturedImageView中的touchedImageView.image中？