New Post: WinRT Blit image quality

Thanks for your reply. Indeed there has been a coordinate issue. :-/ The rects are (horizontal start point, vertical start point, width, height) instead of (horizontal start, vertical start, horizontal end, vertical end). It would be nice if the documentation can be updated.

So it has to be:

dest.DrawInto(backgroundImage, xDestOffset, yDestOffset, 0, 0, backgroundImage.PixelWidth, backgroundImage.PixelHeight);

 public static void DrawInto(this WriteableBitmap dest, WriteableBitmap backgroundImage, int xDestOffset, int yDestOffset, int xstart, int ystart, int xend, int yend)
{
  Rect destRect = new Windows.Foundation.Rect(xDestOffset, yDestOffset, xend-xstart, yend-ystart);
  Rect srcRect = new Windows.Foundation.Rect(xstart, ystart, xend - xstart, yend - ystart);
  dest.Blit(destRect, backgroundImage, srcRect, WriteableBitmapExtensions.BlendMode.None);
 }