qt-everywhere-src-5.15.1/qtbase/examples/widgets/graphicsview/boxes/trackball.cpp

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#include "trackball.h"
#include "scene.h"

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

TrackBall::TrackBall(TrackMode mode)
    : TrackBall(0, QVector3D(0, 1, 0), mode)
{
}

TrackBall::TrackBall(float angularVelocity, const QVector3D& axis, TrackMode mode)
    : m_axis(axis)
    , m_angularVelocity(angularVelocity)
    , m_mode(mode)
{}

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);
            const float angleDelta = qRadiansToDegrees(float(delta.length()));
            m_angularVelocity = angleDelta / msecs;
            m_axis = QVector3D(-delta.dy(), delta.dx(), 0.0f).normalized();
            m_axis = transformation.rotatedVector(m_axis);
            m_rotation = QQuaternion::fromAxisAndAngle(m_axis, angleDelta) * 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 = qRadiansToDegrees(std::asin(m_axis.length()));

            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;
}