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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);
 }