Qt 5.6 | Qt Widgets | Boxes | trackball.cpp Example File

Qt 5.6.2 Reference Documentation

# trackball.cpp Example File

graphicsview/boxes/trackball.cpp

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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;
      }