使用NSBezierPath在NSImageView中画线

if captureFilePath != nil{
    let image: NSImage = getImageFromURL(url: captureFilePath!)!
    image.lockFocus()
    
    NSColor.white.setStroke()
    
    let height: Int = Int(image.size.height)
    let width: Int = Int(image.size.width)
    
    let lineWidth = CGFloat(height > width ? height / 200  + 1: width / 200 + 1)
    
    NSBezierPath.setDefaultLineWidth(lineWidth)
    NSBezierPath.strokeLine(from: NSPoint.init(x: Int(left.stringValue)!, y: 0), to: NSPoint.init(x: Int(left.stringValue)!, y: height))
    NSBezierPath.strokeLine(from: NSPoint.init(x: width - Int(right.stringValue)!, y: 0), to: NSPoint.init(x: width - Int(right.stringValue)!, y: height))
    NSBezierPath.strokeLine(from: NSPoint.init(x: 0, y: Int(bottom.stringValue)!), to: NSPoint.init(x: width, y: Int(bottom.stringValue)!))
    NSBezierPath.strokeLine(from: NSPoint.init(x: 0, y: height - Int(top.stringValue)!), to: NSPoint.init(x: width, y: height - Int(top.stringValue)!))
    
    image.unlockFocus()
    sourceImage.image = image
}

效果如下图，其中白色的线就是用NSBezierPath画的