title: QGraphicsItem.itemClipsChildrenToShape issue in PySide2
body: <p>I'm attempting to create a Smith Chart canvas using a combination of PySide2 and PyQtGraph.
  It seems the best way of doing this as described in this previous question (<a href="https://stackoverflow.com/questions/27479912/pyqtgraph-clip-line">Pyqtgraph clip line</a>) is to use <code>QGraphicsEllipseItem</code> to draw an outer circle, draw all the inner arcs using <code>QGraphicsPathItem</code>  and <code>QPainterPath</code>, then add these to the outer circle and clip them using <code>ItemClipsChildrenToParent</code>.</p>
  <p>Here is my code:</p>
  <pre><code>rline = [0.2, 0.5, 1.0, 2.0, 5.0]
  xline = [0.2, 0.5, 1, 2, 5]
  
  circle1 = QGraphicsEllipseItem(-1, -1, 2, 2)
  circle1.setPen(mkPen('b', width=0.5))
  circle1.setFlag(circle1.ItemClipsChildrenToShape)
  
  pathItem = QGraphicsPathItem()
  path = QPainterPath()
  path.moveTo(1, 0)
  
  for r in rline:
      raggio = 1./(1+r)
      path.addEllipse(1, -raggio, -raggio*2, raggio*2)
  
  for x in xline:
      path.arcTo(1-x, 0, x*2, x*2, 90, 180)
      path.moveTo(1, 0)
      path.arcTo(1-x, 0, x*2, -x*2, 90, 180)
  
  pathItem.setPath(path)
  pathItem.setPen(mkPen('b', width = 0.5))
  pathItem.setParentItem(circle1)
  </code></pre>
  <p>My code appears to be mostly working as shown by the image below.</p>
  <p><a href="https://i.stack.imgur.com/ZUDVR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZUDVR.png" alt="enter image description here" /></a></p>
  <p>The problem is that the inner arcs aren't quite bound by the outer circle. I would have thought that the clipping should be absolute so that the children cannot draw outside of the parents bounds but maybe this is not the case?</p>