knob.cpp Example File

 /****************************************************************************
 **
 ** Copyright (C) 2015 The Qt Company Ltd.
 ** Contact: http://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** 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."
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #include "knob.h"

 #include <QBrush>
 #include <QTouchEvent>

 Knob::Knob()
     : QGraphicsEllipseItem(-50, -50, 100, 100)
 {
     setAcceptTouchEvents(true);
     setBrush(Qt::lightGray);

     QGraphicsEllipseItem *leftItem = new QGraphicsEllipseItem(0, 0, 20, 20, this);
     leftItem->setPos(-40, -10);
     leftItem->setBrush(Qt::darkGreen);

     QGraphicsEllipseItem *rightItem = new QGraphicsEllipseItem(0, 0, 20, 20, this);
     rightItem->setPos(20, -10);
     rightItem->setBrush(Qt::darkRed);
 }

 bool Knob::sceneEvent(QEvent *event)
 {
     switch (event->type()) {
     case QEvent::TouchBegin:
     case QEvent::TouchUpdate:
     case QEvent::TouchEnd:
     {
         QTouchEvent *touchEvent = static_cast<QTouchEvent *>(event);

         if (touchEvent->touchPoints().count() == 2) {
             const QTouchEvent::TouchPoint &touchPoint1 = touchEvent->touchPoints().first();
             const QTouchEvent::TouchPoint &touchPoint2 = touchEvent->touchPoints().last();

             QLineF line1(touchPoint1.lastScenePos(), touchPoint2.lastScenePos());
             QLineF line2(touchPoint1.scenePos(), touchPoint2.scenePos());

             rotate(line2.angleTo(line1));
         }

         break;
     }

     default:
         return QGraphicsItem::sceneEvent(event);
     }

     return true;
 }