Qt 4.8: trackball.cpp Example File (demos/boxes/trackball.cpp)

Qt Reference Documentation

- Qt 4.8
- ALL VERSIONS

- A
- A
- A
- Print

# trackball.cpp Example File

demos/boxes/trackball.cpp

     /****************************************************************************
     **
     ** Copyright (C) 2015 The Qt Company Ltd.
     ** Contact: http://www.qt.io/licensing/
     **
     ** This file is part of the demonstration applications of the Qt Toolkit.
     **
     ** $QT_BEGIN_LICENSE:LGPL$
     ** 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 http://www.qt.io/terms-conditions. For further
     ** information use the contact form at http://www.qt.io/contact-us.
     **
     ** GNU Lesser General Public License Usage
     ** Alternatively, this file may be used under the terms of the GNU Lesser
     ** General Public License version 2.1 or version 3 as published by the Free
     ** Software Foundation and appearing in the file LICENSE.LGPLv21 and
     ** LICENSE.LGPLv3 included in the packaging of this file. Please review the
     ** following information to ensure the GNU Lesser General Public License
     ** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
     ** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
     **
     ** As a special exception, The Qt Company gives you certain additional
     ** rights. These rights are described in The Qt Company LGPL Exception
     ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
     **
     ** GNU General Public License Usage
     ** Alternatively, this file may be used under the terms of the GNU
     ** General Public License version 3.0 as published by the Free Software
     ** Foundation and appearing in the file LICENSE.GPL included in the
     ** packaging of this file.  Please review the following information to
     ** ensure the GNU General Public License version 3.0 requirements will be
     ** met: http://www.gnu.org/copyleft/gpl.html.
     **
     ** $QT_END_LICENSE$
     **
     ****************************************************************************/

     #include "trackball.h"
     #include "scene.h"

     //============================================================================//
     //                                  TrackBall                                 //
     //============================================================================//

     TrackBall::TrackBall(TrackMode mode)
         : m_angularVelocity(0)
         , m_paused(false)
         , m_pressed(false)
         , m_mode(mode)
     {
         m_axis = QVector3D(0, 1, 0);
         m_rotation = QQuaternion();
         m_lastTime = QTime::currentTime();
     }

     TrackBall::TrackBall(float angularVelocity, const QVector3D& axis, TrackMode mode)
         : m_axis(axis)
         , m_angularVelocity(angularVelocity)
         , m_paused(false)
         , m_pressed(false)
         , m_mode(mode)
     {
         m_rotation = QQuaternion();
         m_lastTime = QTime::currentTime();
     }

     void TrackBall::push(const QPointF& p, const QQuaternion &)
     {
         m_rotation = rotation();
         m_pressed = true;
         m_lastTime = QTime::currentTime();
         m_lastPos = p;
         m_angularVelocity = 0.0f;
     }

     void TrackBall::move(const QPointF& p, const QQuaternion &transformation)
     {
         if (!m_pressed)
             return;

         QTime currentTime = QTime::currentTime();
         int msecs = m_lastTime.msecsTo(currentTime);
         if (msecs <= 20)
             return;

         switch (m_mode) {
         case Plane:
             {
                 QLineF delta(m_lastPos, p);
                 m_angularVelocity = 180*delta.length() / (PI*msecs);
                 m_axis = QVector3D(-delta.dy(), delta.dx(), 0.0f).normalized();
                 m_axis = transformation.rotatedVector(m_axis);
                 m_rotation = QQuaternion::fromAxisAndAngle(m_axis, 180 / PI * delta.length()) * m_rotation;
             }
             break;
         case Sphere:
             {
                 QVector3D lastPos3D = QVector3D(m_lastPos.x(), m_lastPos.y(), 0.0f);
                 float sqrZ = 1 - QVector3D::dotProduct(lastPos3D, lastPos3D);
                 if (sqrZ > 0)
                     lastPos3D.setZ(sqrt(sqrZ));
                 else
                     lastPos3D.normalize();

                 QVector3D currentPos3D = QVector3D(p.x(), p.y(), 0.0f);
                 sqrZ = 1 - QVector3D::dotProduct(currentPos3D, currentPos3D);
                 if (sqrZ > 0)
                     currentPos3D.setZ(sqrt(sqrZ));
                 else
                     currentPos3D.normalize();

                 m_axis = QVector3D::crossProduct(lastPos3D, currentPos3D);
                 float angle = 180 / PI * asin(sqrt(QVector3D::dotProduct(m_axis, m_axis)));

                 m_angularVelocity = angle / msecs;
                 m_axis.normalize();
                 m_axis = transformation.rotatedVector(m_axis);
                 m_rotation = QQuaternion::fromAxisAndAngle(m_axis, angle) * m_rotation;
             }
             break;
         }

         m_lastPos = p;
         m_lastTime = currentTime;
     }

     void TrackBall::release(const QPointF& p, const QQuaternion &transformation)
     {
         // Calling move() caused the rotation to stop if the framerate was too low.
         move(p, transformation);
         m_pressed = false;
     }

     void TrackBall::start()
     {
         m_lastTime = QTime::currentTime();
         m_paused = false;
     }

     void TrackBall::stop()
     {
         m_rotation = rotation();
         m_paused = true;
     }

     QQuaternion TrackBall::rotation() const
     {
         if (m_paused || m_pressed)
             return m_rotation;

         QTime currentTime = QTime::currentTime();
         float angle = m_angularVelocity * m_lastTime.msecsTo(currentTime);
         return QQuaternion::fromAxisAndAngle(m_axis, angle) * m_rotation;
     }