ZoomControl.qml Example File

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  import QtQuick 2.0
  import QtMultimedia 5.0

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

      visible: zoomControl.maximumZoom > 1

      MouseArea {
          id : mouseArea
          anchors.fill: parent

          property real initialZoom : 0
          property real initialPos : 0

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

          onPositionChanged: {
              if (pressed) {
                  var target = initialZoom * Math.pow(5, (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

          Rectangle {
              anchors.fill: parent

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

          Rectangle {
              id: groove
              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: "white"
              opacity: 0.5
          }

          Text {
              id: zoomText
              anchors {
                  left: bar.right; leftMargin: 16
              }
              y: Math.min(parent.height - height, Math.max(0, groove.y - height / 2))
              text: "x" + Math.round(zoomControl.currentZoom * 100) / 100
              font.bold: true
              color: "white"
              style: Text.Raised; styleColor: "black"
              opacity: 0.85
              font.pixelSize: 18
          }
      }
  }