trackball.cpp Example File

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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;
 }