Rotations Example

 /****************************************************************************
 **
 ** Copyright (C) 2016 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the Qt Data Visualization module of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:GPL$
 ** Commercial License Usage
 ** Licensees holding valid commercial Qt licenses may use this file in
 ** accordance with the commercial license agreement provided with the
 ** Software or, alternatively, in accordance with the terms contained in
 ** a written agreement between you and The Qt Company. For licensing terms
 ** and conditions see https://www.qt.io/terms-conditions. For further
 ** information use the contact form at https://www.qt.io/contact-us.
 **
 ** GNU General Public License Usage
 ** Alternatively, this file may be used under the terms of the GNU
 ** General Public License version 3 or (at your option) any later version
 ** approved by the KDE Free Qt Foundation. The licenses are as published by
 ** the Free Software Foundation and appearing in the file LICENSE.GPL3
 ** included in the packaging of this file. Please review the following
 ** information to ensure the GNU General Public License requirements will
 ** be met: https://www.gnu.org/licenses/gpl-3.0.html.
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #include "scatterdatamodifier.h"
 #include <QtDataVisualization/qscatterdataproxy.h>
 #include <QtDataVisualization/qvalue3daxis.h>
 #include <QtDataVisualization/q3dscene.h>
 #include <QtDataVisualization/q3dcamera.h>
 #include <QtDataVisualization/qscatter3dseries.h>
 #include <QtDataVisualization/q3dtheme.h>
 #include <QtDataVisualization/QCustom3DItem>
 #include <QtCore/qmath.h>

 using namespace QtDataVisualization;

 static const float verticalRange = 8.0f;
 static const float horizontalRange = verticalRange;
 static const float ellipse_a = horizontalRange / 3.0f;
 static const float ellipse_b = verticalRange;
 static const float doublePi = float(M_PI) * 2.0f;
 static const float radiansToDegrees = 360.0f / doublePi;
 static const float animationFrames = 30.0f;

 ScatterDataModifier::ScatterDataModifier(Q3DScatter *scatter)
     : m_graph(scatter),
       m_fieldLines(12),
       m_arrowsPerLine(16),
       m_magneticField(new QScatter3DSeries),
       m_sun(new QCustom3DItem),
       m_magneticFieldArray(0),
       m_angleOffset(0.0f),
       m_angleStep(doublePi / m_arrowsPerLine / animationFrames)
 {
     m_graph->setShadowQuality(QAbstract3DGraph::ShadowQualityNone);
     m_graph->scene()->activeCamera()->setCameraPreset(Q3DCamera::CameraPresetFront);

     // Magnetic field lines use custom narrow arrow
     m_magneticField->setItemSize(0.2f);
     m_magneticField->setMesh(QAbstract3DSeries::MeshUserDefined);
     m_magneticField->setUserDefinedMesh(QStringLiteral(":/mesh/narrowarrow.obj"));
     QLinearGradient fieldGradient(0, 0, 16, 1024);
     fieldGradient.setColorAt(0.0, Qt::black);
     fieldGradient.setColorAt(1.0, Qt::white);
     m_magneticField->setBaseGradient(fieldGradient);
     m_magneticField->setColorStyle(Q3DTheme::ColorStyleRangeGradient);

     // For 'sun' we use a custom large sphere
     m_sun->setScaling(QVector3D(0.07f, 0.07f, 0.07f));
     m_sun->setMeshFile(QStringLiteral(":/mesh/largesphere.obj"));
     QImage sunColor = QImage(2, 2, QImage::Format_RGB32);
     sunColor.fill(QColor(0xff, 0xbb, 0x00));
     m_sun->setTextureImage(sunColor);

     m_graph->addSeries(m_magneticField);
     m_graph->addCustomItem(m_sun);

     // Configure the axes according to the data
     m_graph->axisX()->setRange(-horizontalRange, horizontalRange);
     m_graph->axisY()->setRange(-verticalRange, verticalRange);
     m_graph->axisZ()->setRange(-horizontalRange, horizontalRange);
     m_graph->axisX()->setSegmentCount(int(horizontalRange));
     m_graph->axisZ()->setSegmentCount(int(horizontalRange));

     QObject::connect(&m_rotationTimer, &QTimer::timeout, this,
                      &ScatterDataModifier::triggerRotation);

     toggleRotation();
     generateData();
 }

 ScatterDataModifier::~ScatterDataModifier()
 {
     delete m_graph;
 }

 void ScatterDataModifier::generateData()
 {
     // Reusing existing array is computationally cheaper than always generating new array, even if
     // all data items change in the array, if the array size doesn't change.
     if (!m_magneticFieldArray)
         m_magneticFieldArray = new QScatterDataArray;

     int arraySize = m_fieldLines * m_arrowsPerLine;
     if (arraySize != m_magneticFieldArray->size())
         m_magneticFieldArray->resize(arraySize);

     QScatterDataItem *ptrToDataArray = &m_magneticFieldArray->first();

     for (float i = 0; i < m_fieldLines; i++) {
         float horizontalAngle = (doublePi * i) / m_fieldLines;
         float xCenter = ellipse_a * qCos(horizontalAngle);
         float zCenter = ellipse_a * qSin(horizontalAngle);

         // Rotate - arrow always tangential to origin
         QQuaternion yRotation = QQuaternion::fromAxisAndAngle(0.0f, 1.0f, 0.0f, horizontalAngle * radiansToDegrees);

         for (float j = 0; j < m_arrowsPerLine; j++) {
             // Calculate point on ellipse centered on origin and parallel to x-axis
             float verticalAngle = ((doublePi * j) / m_arrowsPerLine) + m_angleOffset;
             float xUnrotated = ellipse_a * qCos(verticalAngle);
             float y = ellipse_b * qSin(verticalAngle);

             // Rotate the ellipse around y-axis
             float xRotated = xUnrotated * qCos(horizontalAngle);
             float zRotated = xUnrotated * qSin(horizontalAngle);

             // Add offset
             float x = xCenter + xRotated;
             float z = zCenter + zRotated;

             QQuaternion zRotation = QQuaternion::fromAxisAndAngle(0.0f, 0.0f, 1.0f, verticalAngle * radiansToDegrees);
             QQuaternion totalRotation = yRotation * zRotation;

             ptrToDataArray->setPosition(QVector3D(x, y, z));
             ptrToDataArray->setRotation(totalRotation);
             ptrToDataArray++;
         }
     }

     if (m_graph->selectedSeries() == m_magneticField)
         m_graph->clearSelection();

     m_magneticField->dataProxy()->resetArray(m_magneticFieldArray);
 }

 void ScatterDataModifier::setFieldLines(int lines)
 {
     m_fieldLines = lines;
     generateData();
 }

 void ScatterDataModifier::setArrowsPerLine(int arrows)
 {
     m_angleOffset = 0.0f;
     m_angleStep = doublePi / m_arrowsPerLine / animationFrames;
     m_arrowsPerLine = arrows;
     generateData();
 }

 void ScatterDataModifier::triggerRotation()
 {
     m_angleOffset += m_angleStep;
     generateData();
 }

 void ScatterDataModifier::toggleSun()
 {
     m_sun->setVisible(!m_sun->isVisible());
 }

 void ScatterDataModifier::toggleRotation()
 {
     if (m_rotationTimer.isActive())
         m_rotationTimer.stop();
     else
         m_rotationTimer.start(15);
 }