title: zoomable PKCanvasView with underlaying background image
body: <p>I like to make <code>PKCanvasView</code> to be scrollable and zoomable with underlay image.  It seems it is okay to make it scrollable and zoomable without underlaying background image.  But to make it with underlaying image I don’t know how to make it work.</p>
  
  <p>Since <code>PKCanvasView</code> is a subclass of <code>UIScrollView</code>, I tried place custom content <code>UIView</code> within scroll view, then set a delegate to specify that view for zooming.  But <code>PKCanvasView</code>’s drawing image and content view will not synchronize their positions when zooming, it’s okay with scrolling.</p>
  
  <pre><code>+ UIView (root view)
      + PKCanvasView
          + Custom UIView (underlaying image drawing)
  </code></pre>
  
  <p>Then I tried <code>PKCanvasView</code> as just a content view within another <code>UIScrollView</code>, treat <code>PKCanvasView</code> as non-scrollable view.  Then I synchronize the positions between <code>PKCanvasView</code>’s drawing and container drawing image.  However, I am not sure whether, <code>PKCanvasView</code> may not be designed for being under another <code>UIScrollView</code>, behavior of positioning ruler by finger isn’t stable, kept jumping place to place by dragging.</p>
  
  <pre><code>+ UIView (root view)
      + UIScrollView
          + Custom UIView (underlaying image drawing)
              + PKCanvasView
  </code></pre>
  
  <p>As far as I know, most of <code>PKCanvasView</code> sample code work well without zooming with underlaying image.  But once I set to <code>maximumZoomScale</code> to 2 or more.  Then it no longer synchronize drawings and underlaying background image.</p>
  
  <p>Thanks</p>