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** This file is part of the examples of the Qt Toolkit.
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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)

    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(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 }
            }
        ]
    }
}
