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# trackball.cpp Example File
demos/boxes/trackball.cpp

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     #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;
     }