//MARK:- generate QR code
func generateQRImage(stringQR:NSString,withSizeRate rate:CGFloat) -> UIImage
{
    var filter:CIFilter = CIFilter(name:"CIQRCodeGenerator")
    filter.setDefaults()

    var data:NSData = stringQR.dataUsingEncoding(NSUTF8StringEncoding)!
    filter.setValue(data,forKey: "inputMessage")

    var outputImg:CIImage = filter.outputImage

    var context:CIContext = CIContext(options: nil)
    var cgimg:CGImageRef = context.createCGImage(outputImg,fromRect: outputImg.extent())

    var img:UIImage = UIImage(CGImage: cgimg,scale: 1.0,orientation: UIImageOrientation.Up)!

    var width  = img.size.width * rate
    var height = img.size.height * rate

    UIGraphicsBeginImageContext(CGSizeMake(width,height))
    var cgContxt:CGContextRef = UIGraphicsGetCurrentContext()
    CGContextSetInterpolationQuality(cgContxt,kCGInterpolationNone)
    img.drawInRect(CGRectMake(0,width,height))
    img = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return img
}