ZoomControl.qml Example File

 /****************************************************************************
 **
 ** Copyright (C) 2017 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** Commercial License Usage
 ** Licensees holding valid commercial Qt licenses may use this file in
 ** accordance with the commercial license agreement provided with the
 ** Software or, alternatively, in accordance with the terms contained in
 ** a written agreement between you and The Qt Company. For licensing terms
 ** and conditions see https://www.qt.io/terms-conditions. For further
 ** information use the contact form at https://www.qt.io/contact-us.
 **
 ** BSD License Usage
 ** Alternatively, you may use this file under the terms of the BSD license
 ** as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of The Qt Company Ltd nor the names of its
 **     contributors may be used to endorse or promote products derived
 **     from this software without specific prior written permission.
 **
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 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
         }
     }
 }