- Qt 5.5
- Qt Widgets
- Boxes
- trackball.cpp Example File
- Qt 5.5.1 Reference Documentation

# trackball.cpp Example File

graphicsview/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.
    **
    ** $QT_BEGIN_LICENSE:LGPL21$
    ** Commercial License Usage
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    ** 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
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    #include "trackball.h"
    #include "scene.h"
    #include <cmath>

    //============================================================================//
    //                                  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(std::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(std::sqrt(sqrZ));
                else
                    currentPos3D.normalize();

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