ZoomControl.qml Example File

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 import Qt 4.7
 import QtMultimediaKit 1.1

 Item {
     id : zoomControl
     property real currentZoom : 1
     property real maximumZoom : 1
     signal zoomTo(real value)

     MouseArea {
         id : mouseArea
         anchors.fill: parent

         property real initialZoom : 0
         property real initialPos : 0

         onPressed: {
             initialPos = mouseY
             initialZoom = zoomControl.currentZoom
         }

         onMousePositionChanged: {
             if (pressed) {
                 var target = initialZoom * Math.pow(2, (initialPos-mouseY)/zoomControl.height);
                 target = Math.max(1, Math.min(target, zoomControl.maximumZoom))
                 zoomControl.zoomTo(target)
             }
         }
     }

     Item {
         id : bar
         x : 16
         y : parent.height/4
         width : 24
         height : parent.height/2
         opacity : 0

         Rectangle {
             anchors.fill: parent

             smooth: true
             radius: 8
             border.color: "black"
             border.width: 2
             color: "white"
             opacity: 0.3
         }

         Rectangle {
             x : 0
             y : parent.height * (1.0 - (zoomControl.currentZoom-1.0) / (zoomControl.maximumZoom-1.0))
             width: parent.width
             height: parent.height - y
             smooth: true
             radius: 8
             color: "black"
             opacity: 0.5
         }

         states: State {
             name: "ShowBar"
             when: mouseArea.pressed || zoomControl.currentZoom > 1.0
             PropertyChanges { target: bar; opacity: 1 }
         }

         transitions: [
             Transition {
                 to : "ShowBar"
                 NumberAnimation { properties: "opacity"; duration: 100 }
             },
             Transition {
                 from : "ShowBar"
                 NumberAnimation { properties: "opacity"; duration: 500 }
             }
         ]
     }
 }