trackball.cpp Example File

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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;
  }