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** This file is part of the Qt Quick Extras module of the Qt Toolkit.
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import QtQuick 2.0
import QtGraphicalEffects 1.0
import QtQuick.Controls.Styles 1.4
import QtQuick.Controls.Private 1.0
import QtQuick.Extras.Private 1.1
import QtQuick.Extras.Private.CppUtils 1.0

Control {
    id: root
    x: handleArea.centerOfHandle.x - width / 2
    y: handleArea.centerOfHandle.y - height / 2

    style: Settings.styleComponent(Settings.style, "HandleStyle.qml", root)

    /*!
        The angle of the handle along the circumference of \l rotationRadius in
        radians, scaled to be in the range of 0.0 to 1.0.
    */
    property alias value: range.value

    RangeModel {
        id: range
        minimumValue: 0.0
        maximumValue: 1.0
        stepSize: 0
        value: minimumValue
    }

    /*!
        The angle in radians where the dial starts.
    */
    property real zeroAngle: 0

    /*!
        The radius of the rotation of this handle.
    */
    property real rotationRadius: 50

    /*!
        The center of the dial. This is the origin point for the handle's
        rotation.
    */
    property real dialXCenter: 0
    property real dialYCenter: 0

    /*!
        This property holds the amount of extra room added to each side of
        the handle to make it easier to drag on touch devices.
    */
    property real allowance: Math.max(width, height) * 1.5

    /*
        The function used to determine the handle's value from the position of
        the mouse.

        Can be set to provide custom value calculation. It expects these
        parameters: \c mouseX, \c mouseY, \c xCenter, \c yCenter, \c zeroAngle
    */
    property var valueFromMouse: handleArea.valueFromMouse

    property alias handleArea: handleArea

    MouseArea {
        id: handleArea
        // Respond to value changes by calculating the new center of the handle.
        property point centerOfHandle: MathUtils.centerAlongCircle(dialXCenter, dialYCenter,
            0, 0, MathUtils.valueToAngle(value, 1, zeroAngle), rotationRadius);

        anchors.fill: parent
        anchors.margins: -allowance

        onPositionChanged: {
            // Whenever the handle is moved with the mouse, update the value.
            value = root.valueFromMouse(mouse.x + centerOfHandle.x - allowance,
                mouse.y + centerOfHandle.y - allowance, dialXCenter, dialYCenter, zeroAngle);
        }

        // A helper function for onPositionChanged.
        function valueFromMouse(mouseX, mouseY, xCenter, yCenter, zeroAngle) {
            return MathUtils.angleToValue(
                MathUtils.halfPi - Math.atan2(mouseX - xCenter, mouseY - yCenter), 1, zeroAngle);
        }
    }
}