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

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     #include "trackball.h"

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

     TrackBall::TrackBall(TrackMode mode)
         : m_angularVelocity(0)
         , m_paused(false)
         , m_pressed(false)
         , m_mode(mode)
     {
         m_axis = gfx::Vector3f::vector(0, 1, 0);
         m_rotation = gfx::Quaternionf::quaternion(1.0f, 0.0f, 0.0f, 0.0f);
         m_lastTime = QTime::currentTime();
     }

     TrackBall::TrackBall(float angularVelocity, const gfx::Vector3f& axis, TrackMode mode)
         : m_axis(axis)
         , m_angularVelocity(angularVelocity)
         , m_paused(false)
         , m_pressed(false)
         , m_mode(mode)
     {
         m_rotation = gfx::Quaternionf::quaternion(1.0f, 0.0f, 0.0f, 0.0f);
         m_lastTime = QTime::currentTime();
     }

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

     void TrackBall::move(const QPointF& p, const gfx::Quaternionf &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 = delta.length() / msecs;
                 m_axis = gfx::Vector3f::vector(delta.dy(), -delta.dx(), 0.0f).normalized();
                 m_axis = transformation.transform(m_axis);
                 m_rotation *= gfx::Quaternionf::rotation(delta.length(), m_axis);
             }
             break;
         case Sphere:
             {
                 gfx::Vector3f lastPos3D = gfx::Vector3f::vector(m_lastPos.x(), m_lastPos.y(), 0);
                 float sqrZ = 1 - lastPos3D.sqrNorm();
                 if (sqrZ > 0)
                     lastPos3D[2] = sqrt(sqrZ);
                 else
                     lastPos3D.normalize();

                 gfx::Vector3f currentPos3D = gfx::Vector3f::vector(p.x(), p.y(), 0);
                 sqrZ = 1 - currentPos3D.sqrNorm();
                 if (sqrZ > 0)
                     currentPos3D[2] = sqrt(sqrZ);
                 else
                     currentPos3D.normalize();

                 m_axis = gfx::Vector3f::cross(currentPos3D, lastPos3D);
                 float angle = asin(sqrt(m_axis.sqrNorm()));

                 m_angularVelocity = angle / msecs;
                 m_axis.normalize();
                 m_axis = transformation.transform(m_axis);
                 m_rotation *= gfx::Quaternionf::rotation(angle, m_axis);
             }
             break;
         }

         m_lastPos = p;
         m_lastTime = currentTime;
     }

     void TrackBall::release(const QPointF& p, const gfx::Quaternionf &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;
     }

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

         QTime currentTime = QTime::currentTime();
         float angle = m_angularVelocity * m_lastTime.msecsTo(currentTime);
         return m_rotation * gfx::Quaternionf::rotation(angle, m_axis);
     }