Index out of bounds when calculating pixel index

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C#

I have my image cropping app based on:
http://www.c-sharpcorner.com/UploadFile/55275a/windowsphone-image-crop-with-rectangle/

I modified it a little bit so I can resize rectangle instead of creating new

so my whole method look like:

private async void Accept_Click(object sender, EventArgs e)
  {
      WriteableBitmap wb = new WriteableBitmap(image);

      double originalImageWidth = wb.PixelWidth;
      double originalImageHeight = wb.PixelHeight;

      double displayedWidth = image1.ActualWidth;
      double displayedHeight = image1.ActualHeight;

      double widthRatio = originalImageWidth / displayedWidth;
      double heightRatio = originalImageHeight / displayedHeight;

      r = (Rectangle) (from c in LayoutRoot.Children
                       where c.Opacity == .5 select c).First();

      GeneralTransform gt = r.TransformToVisual(LayoutRoot);
      Point p = gt.Transform(new Point(0, 0));

      Point1 = (r.TransformToVisual(this)).Transform(new Point(0, 0));
      Point2 = new Point(Point1.X + r.Width, Point1.Y + r.Height);

      WriteableBitmap newImage = new WriteableBitmap(
          (int) (widthRatio * Math.Abs(Point2.X - Point1.X)),
          (int) (heightRatio * Math.Abs(Point2.Y - Point1.Y)));

      int xoffset = (int) (((Point1.X < Point2.X) ? Point1.X : Point2.X) * widthRatio);
      int yoffset = (int) (((Point1.Y < Point2.Y) ? Point1.Y : Point2.X) * heightRatio);

      if (newImage.Pixels.Length > 0)
      {
          for (int i = 0; i < newImage.Pixels.Length; i++)
          {
              int x = (int) ((i % newImage.PixelWidth) + xoffset);
              int y = (int) ((i / newImage.PixelWidth) + yoffset);
              newImage.Pixels[i] = wb.Pixels[y * wb.PixelWidth + x];
          }

          using (MemoryStream ms = new MemoryStream())
          {
              newImage.SaveJpeg(ms, (int) newImage.PixelWidth,
                  (int) newImage.PixelHeight, 0, 100);

              image.SetSource(ms);
          }
      }
      else
      {
      }

      ProgressBar pb = new ProgressBar();
      pb.IsEnabled = true;
      LayoutRoot.Children.Add(pb);
      int idReceipt = (int) PhoneApplicationService.Current.State["paragon"];
      await ReceiptsHelper.addPhotosToReceipt(image, idReceipt);
      NavigationService.Navigate(new Uri("/7.0/StronaParagonu.xaml", UriKind.Relative));
  }

When my image is vertical everything works fine, but when my image is horizontal I get Array Index Out Of Bounds Exception at:

newImage.Pixels[i] = wb.Pixels[y * wb.PixelWidth + x];

I don't know exactly what am I doing wrong.

Anybody can help?



EDIT:
I changed my code to:

if (wb.PixelWidth > wb.PixelHeight)     {
    for (int i = 0; i < newImage.Pixels.Length; i++)
    {
        int x = (int)((i % newImage.PixelWidth) + xoffset);
        int y = (int)((i / newImage.PixelWidth) + yoffset);
         newImage.Pixels[i] = wb.Pixels[x * wb.PixelHeight + y];
    }
}
else
{
    for (int i = 0; i < newImage.Pixels.Length; i++)
    {
        int x = (int)((i % newImage.PixelWidth) + xoffset);
        int y = (int)((i / newImage.PixelWidth) + yoffset);
        newImage.Pixels[i] = wb.Pixels[y * wb.PixelWidth + x];
    }
}

In result I've got something like [this](https://assets.okazjum.pl/uploads/uploads/receipt_photo/file/88/s3_2015_9_46_08_PM.jpg)


Maybe there is some workaround in which I can flip image 90 degree?
I tried WriteableBitmapEx but it doesnt work.