New Post: Invalidate not present in WPF

You would need to dispose the context. In WPF the bitmap is invalidated when its unlocked. In WBX the this is done in the dispose call. Use it like this:

        wbmp = BitmapFactory.New(300, 300);
        IMG1.Source = wbmp;
        using(BitmapContext bmpc = wbmp.GetBitmapContext())
        {
            // Clear the WriteableBitmap with white color
            wbmp.Clear(Colors.Red);

            wbmp.DrawLine(0, 0, 1000, 1000, Colors.Black);
        }