title: Offset rotation for QML Item
body: <p>In a QML application I have an item that is moving around the screen (not rotating). I want to display an indicator that rotates around this item, pointing away from the center of the screen, a fixed distance away from the center of the item.</p>
  
  <p><a href="https://i.stack.imgur.com/wIhiP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wIhiP.png" alt=""></a></p>
  
  <p>The following simplified QML application performs this goal, by making the indicator a child of the item, and translating it to the desired location. However, when I try to rotate the indicator (the commented-out code) I cannot find any values for <code>origin.x</code> and <code>.y</code> that work. It feels like the QML scene graph calculates X/Y positioning in a way unlike any I've experienced.</p>
  
  <pre class="lang-qml prettyprint-override"><code>import QtQuick 2.7
  import QtQuick.Window 2.2
  
  Window {
      id: win
      visible:true; width:600; height:300
      property real padding: 50
      property real angle: 0
      property real _rads: angle * Math.PI/180
  
      Timer {
        interval:50; running:true; repeat:true
        onTriggered:win.angle = (new Date/50) % 360
      }
  
      Rectangle {
          id:object; color:'blue'
          width:50; height:width
          property real xOffset: Math.cos(_rads)
          property real yOffset: Math.sin(_rads)
          x: win.width/2  + xOffset * (win.width/2 - padding*2)
          y: win.height/2 + yOffset * (win.height/2 - padding*2)
  
          Rectangle {
              id:indicator; color:'red'
              property real centerOffset: 40
              width:10; height:width*2
              x: object.width/2  + object.xOffset * centerOffset - width/2
              y: object.height/2 + object.yOffset * centerOffset - height/2
  //          transform: Rotation { origin.x:0; origin.y:0; angle:win.angle }
          }
      }
  }
  </code></pre>
  
  <p>I've tried making the indicator not be a child of the item. I've tried using <code>Translate</code> in the <code>transform</code> stack instead of X/Y positions. All of them result in amusing-but-incorrect rotations.</p>
  
  <p><strong>How can I simply rotate the indicator around it's own center, or otherwise achieve my goal?</strong></p>