- Qt 6.12
- Qt Graphs
- Graph Gallery
- Qt Graphs | Commercial or GPLv3

# Graph Gallery

Gallery of Bar, Scatter, and Surface graphs.

Graph Gallery demonstrates all three graph types and some of their special features. The graphs have their own tabs in the application.

#### Running the Example

You can run the example from:

- Qt Creator

  Open the Welcome mode and select the example from Examples. For more information, see Qt Creator: Tutorial: Build and run.

- Qt Extension for Visual Studio Code

  Run the Qt: Open Qt examples command from the Command Palette, and select the example from the list. For more information, see Qt Extension for Visual Studio Code: Tutorial: Build and run.

#### Bar Graph

In the Bar Graph tab, create a 3D bar graph using Q3DBarWidgetItem and combine the use of widgets to adjust various bar graph qualities. The example shows how to:

- Create an application with Q3DBarWidgetItem and some control widgets
- Use QBar3DSeries and QBarDataProxy to set data to the graph
- Adjust some graph and series properties using widget controls
- Select a row or a column by clicking an axis label
- Create a custom proxy to use with Q3DBarWidgetItem

For information about interacting with the graph, see this page.

##### Creating the Application

1. In `bargraph.cpp`, instantiate QQuickWidget and Q3DBarsWidgetItem, and set the QQuickWidget instance as the widget for Q3DBarsWidgetItem:

        m_quickWidget = new QQuickWidget();
        m_barGraph = new Q3DBarsWidgetItem(this);
        m_barGraph->setWidget(m_quickWidget);

2. Create a container widget, and horizontal and vertical layouts. Add the graph and the vertical layout to the horizontal one:

        m_container = new QWidget();
        auto *hLayout = new QHBoxLayout(m_container);
        QSize screenSize = m_quickWidget->screen()->size();
        m_quickWidget->setMinimumSize(QSize(screenSize.width() / 2, screenSize.height() / 1.75));
        m_quickWidget->setMaximumSize(screenSize);
        m_quickWidget->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
        m_quickWidget->setFocusPolicy(Qt::StrongFocus);
        hLayout->addWidget(m_quickWidget, 1);

        auto *vLayout = new QVBoxLayout();
        hLayout->addLayout(vLayout);

3. Create another class to handle the data addition and other interaction with the graph:

        m_modifier = new GraphModifier(m_barGraph, this);

##### Setting up the Bar Graph

1. Set up the graph in the constructor of the `GraphModifier` class:

        GraphModifier::GraphModifier(Q3DBarsWidgetItem *bargraph, QObject *parent)
            : QObject(parent)
            , m_graph(bargraph)

2. Create the axes and the series into member variables to support changing them:

        , m_temperatureAxis(new QValue3DAxis)
        , m_yearAxis(new QCategory3DAxis)
        , m_monthAxis(new QCategory3DAxis)
        , m_primarySeries(new QBar3DSeries)
        , m_secondarySeries(new QBar3DSeries)

3. Set some visual qualities for the graph:

        m_graph->setShadowQuality(QtGraphs3D::ShadowQuality::SoftMedium);
        m_graph->setMultiSeriesUniform(true);
        // These are set through the active theme
        m_graph->activeTheme()->setPlotAreaBackgroundVisible(false);
        m_graph->activeTheme()->setLabelFont(QFont("Times New Roman", m_fontSize));
        m_graph->activeTheme()->setLabelBackgroundVisible(true);

4. Set up the axes and make them the active axes of the graph:

        m_temperatureAxis->setTitle("Average temperature");
        m_temperatureAxis->setSegmentCount(m_segments);
        m_temperatureAxis->setSubSegmentCount(m_subSegments);
        m_temperatureAxis->setRange(m_minval, m_maxval);
        m_temperatureAxis->setLabelFormat(u"%.1f "_s + m_celsiusString);
        m_temperatureAxis->setLabelAutoAngle(30.0f);
        m_temperatureAxis->setTitleVisible(true);

        m_yearAxis->setTitle("Year");
        m_yearAxis->setLabelAutoAngle(30.0f);
        m_yearAxis->setTitleVisible(true);

        m_monthAxis->setTitle("Month");
        m_monthAxis->setLabelAutoAngle(30.0f);
        m_monthAxis->setTitleVisible(true);

        m_graph->setValueAxis(m_temperatureAxis);
        m_graph->setRowAxis(m_yearAxis);
        m_graph->setColumnAxis(m_monthAxis);

5. Give axis labels a small autorotation angle:

        m_yearAxis->setLabelAutoAngle(30.0f);

   This is done to make them orient slightly toward the camera, which improves axis label readability at extreme camera angles.

6. Initialize the visual properties of the series. Note that the second series is initially not visible:

        m_primarySeries->setItemLabelFormat(u"Oulu - @colLabel @rowLabel: @valueLabel"_s);
        m_primarySeries->setMesh(QAbstract3DSeries::Mesh::BevelBar);
        m_primarySeries->setMeshSmooth(false);

        m_secondarySeries->setItemLabelFormat(u"Helsinki - @colLabel @rowLabel: @valueLabel"_s);
        m_secondarySeries->setMesh(QAbstract3DSeries::Mesh::BevelBar);
        m_secondarySeries->setMeshSmooth(false);
        m_secondarySeries->setVisible(false);

7. Add the series to the graph:

        m_graph->addSeries(m_primarySeries);
        m_graph->addSeries(m_secondarySeries);

8. Set the camera angle by calling the same method the camera angle change button in the UI uses to cycle through various camera angles:

        changePresetCamera();

9. The new camera preset is set to the graph:

        static int preset = int(QtGraphs3D::CameraPreset::Front);

        m_graph->setCameraPreset((QtGraphs3D::CameraPreset) preset);

        if (++preset > int(QtGraphs3D::CameraPreset::DirectlyBelow))
            preset = int(QtGraphs3D::CameraPreset::FrontLow);

##### Adding Data to the Graph

At the end of the constructor, call a method that sets up the data:

     resetTemperatureData();

This method adds data to the relevant series using proxies of the two series:

     // Set up data
     static const float tempOulu[8][12] = {
         {-7.4f, -2.4f, 0.0f, 3.0f, 8.2f, 11.6f, 14.7f, 15.4f, 11.4f, 4.2f, 2.1f, -2.3f},     // 2015
         {-13.4f, -3.9f, -1.8f, 3.1f, 10.6f, 13.7f, 17.8f, 13.6f, 10.7f, 3.5f, -3.1f, -4.2f}, // 2016
     ...
     QBarDataArray dataSet;
     QBarDataArray dataSet2;

     dataSet.reserve(m_years.size());
     for (qsizetype year = 0; year < m_years.size(); ++year) {
         // Create a data row
         QBarDataRow dataRow(m_months.size());
         QBarDataRow dataRow2(m_months.size());
         for (qsizetype month = 0; month < m_months.size(); ++month) {
             // Add data to the row
             dataRow[month].setValue(tempOulu[year][month]);
             dataRow2[month].setValue(tempHelsinki[year][month]);
         }
         // Add the row to the set
         dataSet.append(dataRow);
         dataSet2.append(dataRow2);
     }

     // Add data to the data proxy (the data proxy assumes ownership of it)
     m_primarySeries->dataProxy()->resetArray(dataSet, m_years, m_months);
     m_secondarySeries->dataProxy()->resetArray(dataSet2, m_years, m_months);

##### Using Widgets to Control the Graph

Continue by adding some widgets in `bargraph.cpp`.

1. Add a slider:

        auto *rotationSliderX = new QSlider(Qt::Horizontal, m_container);
        rotationSliderX->setTickInterval(30);
        rotationSliderX->setTickPosition(QSlider::TicksBelow);
        rotationSliderX->setMinimum(-180);
        rotationSliderX->setValue(0);
        rotationSliderX->setMaximum(180);

2. Use the slider to rotate the graph instead of just using a mouse or touch. Add it to the vertical layout:

        vLayout->addWidget(new QLabel(u"Rotate horizontally"_s));
        vLayout->addWidget(rotationSliderX, 0, Qt::AlignTop);

3. Connect it to a method in `GraphModifier`:

        QObject::connect(rotationSliderX, &QSlider::valueChanged, m_modifier, &GraphModifier::rotateX);

4. Create a slot in `GraphModifier` for the signal connection. Specify the actual camera position along the orbit around the center point, instead of specifying a preset camera angle:

        void GraphModifier::rotateX(int angle)
        {
            m_xRotation = angle;
            m_graph->setCameraPosition(m_xRotation, m_yRotation);
        }

You can now use the slider to rotate the graph.

Add more widgets to the vertical layout to control:

- Graph rotation
- Label style
- Camera preset
- Background visibility
- Grid visibility
- Bar shading smoothness
- Visibility of the second bar series
- Value axis direction
- Axis title visibility and rotation
- Data range to be shown
- Bar style
- Selection mode
- Theme
- Shadow quality
- Font
- Font size
- Axis label rotation
- Data mode

Some widget controls are intentionally disabled when in the Custom Proxy Data data mode.

##### Selecting a Row or Column by Clicking an Axis Label

Selection by axis label is default functionality for bar graphs. For example, you can select rows by clicking an axis label in the following way:

1. Change selection mode to `Row`
2. Click a year label
3. The row with the clicked year is selected

The same method works with `Slice` and `Item` flags, as long as either `Row` or `Column` is set as well.

##### Zooming to Selection

As an example of adjusting the camera target, implement an animation of zooming to selection via a button press. Animation initializations are done in the constructor:

     m_defaultAngleX = m_graph->cameraXRotation();
     m_defaultAngleY = m_graph->cameraYRotation();
     m_defaultZoom = m_graph->cameraZoomLevel();
     m_defaultTarget = m_graph->cameraTargetPosition();

     m_animationCameraX.setTargetObject(m_graph);
     m_animationCameraY.setTargetObject(m_graph);
     m_animationCameraZoom.setTargetObject(m_graph);
     m_animationCameraTarget.setTargetObject(m_graph);

     m_animationCameraX.setPropertyName("cameraXRotation");
     m_animationCameraY.setPropertyName("cameraYRotation");
     m_animationCameraZoom.setPropertyName("cameraZoomLevel");
     m_animationCameraTarget.setPropertyName("cameraTargetPosition");

     int duration = 1700;
     m_animationCameraX.setDuration(duration);
     m_animationCameraY.setDuration(duration);
     m_animationCameraZoom.setDuration(duration);
     m_animationCameraTarget.setDuration(duration);

     // The zoom always first zooms out above the graph and then zooms in
     qreal zoomOutFraction = 0.3;
     m_animationCameraX.setKeyValueAt(zoomOutFraction, QVariant::fromValue(0.0f));
     m_animationCameraY.setKeyValueAt(zoomOutFraction, QVariant::fromValue(90.0f));
     m_animationCameraZoom.setKeyValueAt(zoomOutFraction, QVariant::fromValue(50.0f));
     m_animationCameraTarget.setKeyValueAt(zoomOutFraction,
                                           QVariant::fromValue(QVector3D(0.0f, 0.0f, 0.0f)));

Function `GraphModifier::zoomToSelectedBar()` contains the zooming functionality. QPropertyAnimation `m_animationCameraTarget` targets cameraTargetPosition property, which takes a value normalized to the range (-1, 1).

Figure out where the selected bar is relative to axes, and use that as the end value for `m_animationCameraTarget`:

     QVector3D endTarget;
     float xMin = m_graph->columnAxis()->min();
     float xRange = m_graph->columnAxis()->max() - xMin;
     float zMin = m_graph->rowAxis()->min();
     float zRange = m_graph->rowAxis()->max() - zMin;
     endTarget.setX((selectedBar.y() - xMin) / xRange * 2.0f - 1.0f);
     endTarget.setZ((selectedBar.x() - zMin) / zRange * 2.0f - 1.0f);
     ...
     m_animationCameraTarget.setEndValue(QVariant::fromValue(endTarget));

Then, rotate the camera so that it always points approximately to the center of the graph at the end of the animation:

     qreal endAngleX = 90.0 - qRadiansToDegrees(qAtan(qreal(endTarget.z() / endTarget.x())));
     if (endTarget.x() > 0.0f)
         endAngleX -= 180.0f;
     float barValue = m_graph->selectedSeries()
                          ->dataProxy()
                          ->itemAt(selectedBar.x(), selectedBar.y())
                          .value();
     float endAngleY = barValue >= 0.0f ? 30.0f : -30.0f;
     if (m_graph->valueAxis()->reversed())
         endAngleY *= -1.0f;

##### Model Proxy for Data

When you toggle Model Proxy Data data mode on, the graph in the example uses an item model based dataset and the corresponding proxy.

###### RainfallData

Class `RainfallData` sets up a QItemModelBarDataProxy along with the series and axes.

1. We use a `std::array<double, 12>` to store the values of a year indexed by month. The static `readData()` helper function reads the data, returning a QList of them indexed by year:

        using YearlyData = std::array<double, 12>;
        using ModelData = QList<YearlyData>;

        static ModelData readData(const QString &fileName, int *firstYear)
        {
            ModelData result;

            *firstYear = -1;

            // Read data from a data file into the data item list
            QFile dataFile(fileName);
            if (!dataFile.open(QIODevice::ReadOnly | QIODevice::Text)) {
                qWarning() << "Unable to open data file:" << dataFile.fileName() << dataFile.errorString();
                return result;
            }

            QTextStream stream(&dataFile);
            int lastYear = -1;
            while (!stream.atEnd()) {
                QString line = stream.readLine();
                if (line.startsWith(u'#')) // Ignore comments
                    continue;
                const auto strList = QStringView{line}.split(',', Qt::SkipEmptyParts);
                // Each line has three data items: Year, month, and rainfall value
                if (strList.size() < 3) {
                    qWarning() << "Invalid row read from data:" << line;
                    continue;
                }
                // Store year and month as int, and rainfall value as double
                bool yearOk{};
                bool monthOk{};
                bool valueOk{};
                const int year = strList.at(0).trimmed().toInt(&yearOk);
                const int month = strList.at(1).trimmed().toInt(&monthOk);
                const double value = strList.at(2).trimmed().toDouble(&valueOk);
                if (!yearOk || !monthOk || month < 1 || month > 12 || !valueOk) {
                    qWarning() << "Invalid row values:" << line;
                    continue;
                }
                if (year != lastYear) {
                    if (lastYear == -1) {
                        *firstYear = year;
                    } else if (year != lastYear + 1) {
                        qWarning() << "Non-consecutive years" << year << lastYear;
                        return {};
                    }
                    lastYear = year;
                    result.emplace_back(YearlyData{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});
                }
                result.back()[month - 1] = value;
            }
            return result;
        }
            ...

2. The QList represents a two dimensional array indexed by year and month, respectively. From this, we populate a QRangeModel and pass it to a QItemModelBarDataProxy() in the `RainfallData` class:

        int firstYear{};
        auto data = readData(":/data/raindata.txt"_L1, &firstYear);
        Q_ASSERT(!data.isEmpty());
        updateYearsList(firstYear, firstYear + int(data.size()) - 1);
        auto *model = new QRangeModel(data, this);

        m_proxy = new QItemModelBarDataProxy(model);
        m_proxy->setUseModelCategories(true);
        m_series = new QBar3DSeries(m_proxy);

3. Finally, add a function for getting the created series for displaying:

        QBar3DSeries *customSeries() { return m_series; }

#### Scatter Graph

In the Scatter Graph tab, create a 3D scatter graph using Q3DScatterWidgetItem. The example shows how to:

- Set up Q3DScatterWidgetItem graph
- Use QScatterDataProxy to set data to the graph
- Create and add a custom input handler

For basic application creation, see Bar Graph.

##### Setting up the Scatter Graph

1. Set up some visual qualities for the graph in the constructor of the `ScatterDataModifier`:

        m_graph->setShadowQuality(QtGraphs3D::ShadowQuality::SoftHigh);
        m_graph->setCameraPreset(QtGraphs3D::CameraPreset::Front);
        m_graph->setCameraZoomLevel(80.f);
        // These are set through active theme
        m_graph->activeTheme()->setTheme(QGraphsTheme::Theme::MixSeries);
        m_graph->activeTheme()->setColorScheme(QGraphsTheme::ColorScheme::Dark);

   None of these settings are mandatory, but they serve to override graph defaults. To observe the appearance with the preset defaults, the block above can be commented out.

2. Create a QScatterDataProxy and the associated QScatter3DSeries. Set a custom label format and mesh smoothing for the series and add it to the graph:

        auto *proxy = new QScatterDataProxy;
        auto *series = new QScatter3DSeries(proxy);
        series->setItemLabelFormat(u"@xTitle: @xLabel @yTitle: @yLabel @zTitle: @zLabel"_s);
        series->setMeshSmooth(m_smooth);
        m_graph->addSeries(series);

##### Adding Scatter Data

1. In the `ScatterDataModifier` constructor, add data to the graph:

        addData();

2. The actual data addition is done in `addData()` method. First, configure the axes:

        m_graph->axisX()->setTitle("X");
        m_graph->axisY()->setTitle("Y");
        m_graph->axisZ()->setTitle("Z");

   You could do this also in the constructor of `ScatterDataModifier`. Doing it here keeps the constructor simpler and the axes' configuration near the data.

3. Create a data array and populate it:

        QScatterDataArray dataArray;
        dataArray.reserve(m_itemCount);
            ...
        const float limit = qSqrt(m_itemCount) / 2.0f;
        for (int i = -limit; i < limit; ++i) {
            for (int j = -limit; j < limit; ++j) {
                const float x = float(i) + 0.5f;
                const float y = qCos(qDegreesToRadians(float(i * j) / m_curveDivider));
                const float z = float(j) + 0.5f;
                dataArray.append(QScatterDataItem(x, y, z));
            }
        }

4. Finally, tell the proxy to start using the data we gave it:

        m_graph->seriesList().at(0)->dataProxy()->resetArray(dataArray);

Now, the graph has the data and is ready for use. For information about adding widgets to control the graph, see Using Widgets to Control the Graph.

##### Replacing Default Input Handling

To replace the default input handling mechanism, set the new input handlers of Q3DScatterWidgetItem, which implements the custom behavior:

     connect(m_graph,
             &Q3DGraphsWidgetItem::selectedElementChanged,
             this,
             &ScatterDataModifier::handleElementSelected);
     connect(m_graph, &Q3DGraphsWidgetItem::dragged, this, &ScatterDataModifier::handleAxisDragging);
     m_graph->setDragButton(Qt::LeftButton);

##### Extending Mouse Event Handling

Implement a new `drag` event handler. It provides a mouse movement distance for the axis dragging calculation (see Implementing Axis Dragging for details):

     connect(m_graph,
             &Q3DGraphsWidgetItem::selectedElementChanged,
             this,
             &ScatterDataModifier::handleElementSelected);
     connect(m_graph, &Q3DGraphsWidgetItem::dragged, this, &ScatterDataModifier::handleAxisDragging);
     m_graph->setDragButton(Qt::LeftButton);

##### Implementing Axis Dragging

1. Start listening to the selection signal from the graph. Do that in the constructor, and connect it to the `handleElementSelected` method:

        connect(m_graph,
                &Q3DGraphsWidgetItem::selectedElementChanged,
                this,
                &ScatterDataModifier::handleElementSelected);
        connect(m_graph, &Q3DGraphsWidgetItem::dragged, this, &ScatterDataModifier::handleAxisDragging);
        m_graph->setDragButton(Qt::LeftButton);

2. In `handleElementSelected`, check the type of the selection, and set the internal state based on it:

        switch (type) {
        case QtGraphs3D::ElementType::AxisXLabel:
            m_state = StateDraggingX;
            break;
        case QtGraphs3D::ElementType::AxisYLabel:
            m_state = StateDraggingY;
            break;
        case QtGraphs3D::ElementType::AxisZLabel:
            m_state = StateDraggingZ;
            break;
        default:
            m_state = StateNormal;
            break;
        }

3. The actual dragging logic is implemented in the `handleAxisDragging` method, which is called from `drag` event:

        void ScatterDataModifier::handleAxisDragging(QVector2D delta)

4. In `handleAxisDragging`, first get the scene orientation from the active camera:

        // Get scene orientation from active camera
        float xRotation = m_graph->cameraXRotation();
        float yRotation = m_graph->cameraYRotation();

5. Calculate the modifiers for mouse movement direction based on the orientation:

        // Calculate directional drag multipliers based on rotation
        float xMulX = qCos(qDegreesToRadians(xRotation));
        float xMulY = qSin(qDegreesToRadians(xRotation));
        float zMulX = qSin(qDegreesToRadians(xRotation));
        float zMulY = qCos(qDegreesToRadians(xRotation));

6. Calculate the mouse movement, and modify it based on the y rotation of the camera:

        // Get the drag amount
        QPoint move = delta.toPoint();

        // Flip the effect of y movement if we're viewing from below
        float yMove = (yRotation < 0) ? -move.y() : move.y();

7. Apply the moved distance to the correct axis:

        // Adjust axes
        QValue3DAxis *axis = nullptr;
        switch (m_state) {
        case StateDraggingX:
            axis = m_graph->axisX();
            distance = (move.x() * xMulX - yMove * xMulY) / m_dragSpeedModifier;
            axis->setRange(axis->min() - distance, axis->max() - distance);
            break;
        case StateDraggingZ:
            axis = m_graph->axisZ();
            distance = (move.x() * zMulX + yMove * zMulY) / m_dragSpeedModifier;
            axis->setRange(axis->min() + distance, axis->max() + distance);
            break;
        case StateDraggingY:
            axis = m_graph->axisY();
            distance = move.y() / m_dragSpeedModifier; // No need to use adjusted y move here
            axis->setRange(axis->min() + distance, axis->max() + distance);
            break;
        default:
            break;
        }

#### Surface Graph

In the Surface Graph tab, create a 3D surface graph using Q3DSurfaceWidgetItem. The example shows how to:

- Set up a basic QSurfaceDataProxy and set data for it.
- Use QHeightMapSurfaceDataProxy for showing 3D height maps.
- Use topographic data to create 3D height maps.
- Use three different selection modes for studying the graph.
- Use axis ranges to display selected portions of the graph.
- Set a custom surface gradient.
- Add custom items and labels with QCustom3DItem and QCustom3DLabel.
- Use custom input handler to enable zooming and panning.
- Highlight an area of the surface.

For basic application creation, see Bar Graph.

##### Simple Surface with Generated Data

1. First, instantiate a new QSurfaceDataProxy and attach it to a new QSurface3DSeries:

        m_sqrtSinProxy = new QSurfaceDataProxy();
        m_sqrtSinSeries = new QSurface3DSeries(m_sqrtSinProxy);

2. Fill the proxy with a simple square root and sine wave data. Create a `QSurfaceDataArray` instance and add `QSurfaceDataRow` elements to it. Set the created `QSurfaceDataArray` as the data array for the QSurfaceDataProxy by calling `resetArray()`.

        QSurfaceDataArray dataArray;
        dataArray.reserve(sampleCountZ);
        for (int i = 0; i < sampleCountZ; ++i) {
            QSurfaceDataRow newRow;
            newRow.reserve(sampleCountX);
            // Keep values within range bounds, since just adding step can cause minor
            // drift due to the rounding errors.
            float z = qMin(sampleMax, (i * stepZ + sampleMin));
            for (int j = 0; j < sampleCountX; ++j) {
                float x = qMin(sampleMax, (j * stepX + sampleMin));
                float R = qSqrt(z * z + x * x) + 0.01f;
                float y = (qSin(R) / R + 0.24f) * 1.61f;
                newRow.append(QSurfaceDataItem(x, y, z));
            }
            dataArray.append(newRow);
        }

        m_sqrtSinProxy->resetArray(dataArray);

##### Multiseries Height Map Data

Create the height map by instantiating a QHeightMapSurfaceDataProxy with a QImage containing the height data. Use QHeightMapSurfaceDataProxy::setValueRanges() to define the value range of the map. In the example, the map is from an imaginary position of 34.0° N - 40.0° N and 18.0° E - 24.0° E. These values are used to position the map on the axes.

     // Create the first surface layer
     QImage heightMapImageOne(":/data/layer_1.png");
     m_heightMapProxyOne = new QHeightMapSurfaceDataProxy(heightMapImageOne);
     m_heightMapSeriesOne = new QSurface3DSeries(m_heightMapProxyOne);
     m_heightMapSeriesOne->setItemLabelFormat(u"(@xLabel, @zLabel): @yLabel"_s);
     m_heightMapProxyOne->setValueRanges(34.f, 40.f, 18.f, 24.f);

Add the other surface layers the same way, by creating a proxy and a series for them using height map images. -

##### Topographic Map Data

The topographic data is obtained from the National Land Survey of Finland. It provides a product called `Elevation Model 2 m`, which is suitable for this example.

The topography data is from Levi fell. The accuracy of the data is well beyond the need, and therefore it is compressed and encoded into a PNG file. The height value of the original ASCII data is encoded into RGB format using a multiplier, as demonstrated in the code sample below. The multiplier is calculated by dividing the largest 24-bit value with the highest point in Finland.

QHeightMapSurfaceDataProxy converts only one-byte values. To utilize the higher accuracy of the data from the National Land Survey of Finland, read the data from the PNG file and decode it into a QSurface3DSeries.

1. Define the encoding multiplier:

        // Value used to encode height data as RGB value on PNG file
        const float packingFactor = 11983.f;

2. Perform the actual decoding:

        QImage heightMapImage(file);
        uchar *bits = heightMapImage.bits();
        int imageHeight = heightMapImage.height();
        int imageWidth = heightMapImage.width();
        int widthBits = imageWidth * 4;
        float stepX = width / float(imageWidth);
        float stepZ = height / float(imageHeight);

        QSurfaceDataArray dataArray;
        dataArray.reserve(imageHeight);
        for (int i = 0; i < imageHeight; ++i) {
            int p = i * widthBits;
            float z = height - float(i) * stepZ;
            QSurfaceDataRow newRow;
            newRow.reserve(imageWidth);
            for (int j = 0; j < imageWidth; ++j) {
                uchar aa = bits[p + 0];
                uchar rr = bits[p + 1];
                uchar gg = bits[p + 2];
                uint color = uint((gg << 16) + (rr << 8) + aa);
                float y = float(color) / packingFactor;
                newRow.append(QSurfaceDataItem(float(j) * stepX, y, z));
                p += 4;
            }
            dataArray.append(newRow);
        }

        dataProxy()->resetArray(dataArray);

Now, a Surface Graph can consume the data via the proxy.

##### Selecting the Data Set

To demonstrate different proxies, the Surface Graph has three radio buttons to switch between the series.

With Sqrt & Sin, the simple generated series is activated.

1. Set the decorative features, such as enabling the grid for the surface, and selecting the flat shading mode.
2. Define the axis label format and value ranges. Set automatic label rotation to improve label readability at low camera angles.
3. Make sure the correct series is added to the graph and the others are not.

     m_sqrtSinSeries->setDrawMode(QSurface3DSeries::DrawSurfaceAndWireframe);
     m_sqrtSinSeries->setShading(QSurface3DSeries::Shading::Flat);

     m_graph->axisX()->setLabelFormat("%.2f");
     m_graph->axisZ()->setLabelFormat("%.2f");
     m_graph->axisX()->setRange(sampleMin, sampleMax);
     m_graph->axisY()->setRange(0.f, 2.f);
     m_graph->axisZ()->setRange(sampleMin, sampleMax);
     m_graph->axisX()->setLabelAutoAngle(30.f);
     m_graph->axisY()->setLabelAutoAngle(90.f);
     m_graph->axisZ()->setLabelAutoAngle(30.f);

     m_graph->removeSeries(m_heightMapSeriesOne);
     m_graph->removeSeries(m_heightMapSeriesTwo);
     m_graph->removeSeries(m_heightMapSeriesThree);
     m_graph->removeSeries(m_topography);
     m_graph->removeSeries(m_highlight);

     m_graph->addSeries(m_sqrtSinSeries);

With Multiseries Height Map, the height map series are activated and others are disabled. Auto-adjusting the Y-axis range works well for the height map surface, so ensure it is set.

     m_graph->axisY()->setAutoAdjustRange(true);

With Textured Topography, the topographic series is activated and others are disabled. Activate a custom input handler for this series, to be able to highlight areas on it:

     m_graph->setDragButton(Qt::LeftButton);
     QObject::connect(m_graph,
                      &Q3DGraphsWidgetItem::dragged,
                      this,
                      &SurfaceGraphModifier::handleAxisDragging);

     QObject::connect(m_graph,
                      &Q3DGraphsWidgetItem::wheel,
                      this,
                      &SurfaceGraphModifier::onWheel);
     m_graph->setZoomEnabled(false);

See Use Custom Input Handler to Enable Zooming and Panning for information about the custom input handler for this data set.

##### Selection Modes

The three selection modes supported by Q3DSurfaceWidgetItem can be used with radio buttons. To activate the selected mode or to clear it, add the following inline methods:

     void toggleModeNone() { m_graph->setSelectionMode(QtGraphs3D::SelectionFlag::None); }
     void toggleModeItem() { m_graph->setSelectionMode(QtGraphs3D::SelectionFlag::Item); }
     void toggleModeSliceRow()
     {
         m_graph->setSelectionMode(QtGraphs3D::SelectionFlag::ItemAndRow
                                   | QtGraphs3D::SelectionFlag::Slice
                                   | QtGraphs3D::SelectionFlag::MultiSeries);
     }
     void toggleModeSliceColumn()
     {
         m_graph->setSelectionMode(QtGraphs3D::SelectionFlag::ItemAndColumn
                                   | QtGraphs3D::SelectionFlag::Slice
                                   | QtGraphs3D::SelectionFlag::MultiSeries);
     }

To support doing a slice selection to all visible series in the graph simultaneously, add `QtGraphs3D::SelectionFlag::Slice` and `QtGraphs3D::SelectionFlag::MultiSeries` flags for the row and column selection modes.

##### Axis Ranges for Studying the Graph

The example has four slider controls for adjusting the min and max values for the X and Z axes. When selecting the proxy, these sliders are adjusted to match the axis ranges of the current data set:

     // Reset range sliders for Sqrt & Sin
     m_rangeMinX = sampleMin;
     m_rangeMinZ = sampleMin;
     m_stepX = (sampleMax - sampleMin) / float(sampleCountX - 1);
     m_stepZ = (sampleMax - sampleMin) / float(sampleCountZ - 1);
     m_axisMinSliderX->setMinimum(0);
     m_axisMinSliderX->setMaximum(sampleCountX - 2);
     m_axisMinSliderX->setValue(0);
     m_axisMaxSliderX->setMinimum(1);
     m_axisMaxSliderX->setMaximum(sampleCountX - 1);
     m_axisMaxSliderX->setValue(sampleCountX - 1);
     m_axisMinSliderZ->setMinimum(0);
     m_axisMinSliderZ->setMaximum(sampleCountZ - 2);
     m_axisMinSliderZ->setValue(0);
     m_axisMaxSliderZ->setMinimum(1);
     m_axisMaxSliderZ->setMaximum(sampleCountZ - 1);
     m_axisMaxSliderZ->setValue(sampleCountZ - 1);

To add support for setting the X range from the widget controls to the graph, add:

     void SurfaceGraphModifier::setAxisXRange(float min, float max)
     {
         m_graph->axisX()->setRange(min, max);
     }

Add the support for Z range the same way.

##### Custom Surface Gradients

With the Sqrt & Sin data set, custom surface gradients can be taken into use with two push buttons. Define the gradient with QLinearGradient, where the desired colors are set. Also, change the color style to Q3DTheme::ColorStyle::RangeGradient to use the gradient.

     QLinearGradient gr;
     gr.setColorAt(0.f, Qt::black);
     gr.setColorAt(0.33f, Qt::blue);
     gr.setColorAt(0.67f, Qt::red);
     gr.setColorAt(1.f, Qt::yellow);

     m_sqrtSinSeries->setBaseGradient(gr);
     m_sqrtSinSeries->setColorStyle(QGraphsTheme::ColorStyle::RangeGradient);

##### Adding Custom Meshes to the Application

To add custom meshes tp the application:

- For a cmake build. Add the mesh files to `CMakeLists.txt`:

       set(graphgallery_resource_files
           ...
           "data/oilrig.mesh"
           "data/pipe.mesh"
           "data/refinery.mesh"
           ...
       )

       qt6_add_resources(widgetgraphgallery "widgetgraphgallery"
           PREFIX
               "/"
           FILES
               ${graphgallery_resource_files}
       )

- For a qmake build. Add the mesh files in the qrc resource file:

       <RCC>
           <qresource prefix="/">
               ...
               <file>data/refinery.mesh</file>
               <file>data/oilrig.mesh</file>
               <file>data/pipe.mesh</file>
               ...
           </qresource>
       </RCC>

##### Adding Custom Item to a Graph

With the Multiseries Height Map data set, custom items are inserted into the graph and can be toggled on or off using checkboxes. Other visual changes can also be controlled with another set of checkboxes, including see-through for the two top layers, and a highlight for the bottom layer.

- Creating a small QImage. Fill it with a single color to use as the color for the custom object:

       QImage color = QImage(2, 2, QImage::Format_RGB32);
       color.fill(Qt::red);

- Specify the position of the item in a variable. The position can then be used for removing the correct item from the graph:

       QVector3D positionOne = QVector3D(39.f, 77.f, 19.2f);

- Create a new QCustom3DItem with all the parameters:

       auto *item = new QCustom3DItem(":/data/oilrig.mesh",
                                      positionOne,
                                      QVector3D(0.0125f, 0.0125f, 0.0125f),
                                      QQuaternion::fromAxisAndAngle(0.f, 1.f, 0.f, 45.f),
                                      color);

- Add the item to the graph:

       m_graph->addCustomItem(item);

##### Adding Custom Label to a Graph

Adding a custom label is very similar to adding a custom item. For the label, a custom mesh is not needed, but just a QCustom3DLabel instance:

     auto *label = new QCustom3DLabel();
     label->setText("Oil Rig One");
     label->setPosition(positionOneLabel);
     label->setScaling(QVector3D(1.f, 1.f, 1.f));
     m_graph->addCustomItem(label);

##### Removing Custom Item from a Graph

To remove a specific item from the graph, call `removeCustomItemAt()` with the position of the item:

     m_graph->removeCustomItemAt(positionOne);

Note: Removing a custom item from the graph also deletes the object. To preserve the item, use the `releaseCustomItem()` method instead.

##### Texture to a Surface Series

With the Textured Topography data set, create a map texture to be used with the topographic height map.

Set an image to be used as the texture on a surface with QSurface3DSeries::setTextureFile(). Add a check box to control if the texture is set or not, and a handler to react to the checkbox state:

     void SurfaceGraphModifier::toggleSurfaceTexture(bool enable)
     {
         if (enable)
             m_topography->setTextureFile(":/data/maptexture.jpg");
         else
             m_topography->setTextureFile("");
     }

The image in this example is read from a JPG file. Setting an empty file with the method clears the texture, and the surface uses the gradients or colors from the theme.

##### Use Custom Input Handler to Enable Zooming and Panning

With the Textured Topography data set, create a custom input handler to highlight the selection on the graph and allow panning the graph.

The panning implementation is similar to the one shown in Implementing Axis Dragging. The difference is that, in this example, you only follow the X and Z axes and don't allow dragging the surface outside the graph. To limit the dragging, follow the limits of the axes and do nothing if going outside the graph:

     case StateDraggingX:
         distance = (move.x() * xMulX - move.y() * xMulY) * m_speedModifier;
         m_axisXMinValue -= distance;
         m_axisXMaxValue -= distance;
         if (m_axisXMinValue < m_areaMinValue) {
             float dist = m_axisXMaxValue - m_axisXMinValue;
             m_axisXMinValue = m_areaMinValue;
             m_axisXMaxValue = m_axisXMinValue + dist;
         }
         if (m_axisXMaxValue > m_areaMaxValue) {
             float dist = m_axisXMaxValue - m_axisXMinValue;
             m_axisXMaxValue = m_areaMaxValue;
             m_axisXMinValue = m_axisXMaxValue - dist;
         }
         m_graph->axisX()->setRange(m_axisXMinValue, m_axisXMaxValue);
         break;

For zooming, catch the `wheelEvent` and adjust the X and Y axis ranges according to the delta value on QWheelEvent. Adjust the Y axis so that the aspect ratio between the Y axis and the XZ plane stays the same. This prevents getting a graph in which the height is exaggerated:

     void SurfaceGraphModifier::onWheel(QWheelEvent *event)
     {
         float delta = float(event->angleDelta().y());

         m_axisXMinValue += delta;
         m_axisXMaxValue -= delta;
         m_axisZMinValue += delta;
         m_axisZMaxValue -= delta;
         checkConstraints();

         float y = (m_axisXMaxValue - m_axisXMinValue) * m_aspectRatio;

         m_graph->axisX()->setRange(m_axisXMinValue, m_axisXMaxValue);
         m_graph->axisY()->setRange(100.f, y);
         m_graph->axisZ()->setRange(m_axisZMinValue, m_axisZMaxValue);
     }

Next, add some limits to the zoom level, so that it won't get too near to or far from the surface. For instance, if the value for the X axis gets below the allowed limit, that is, zooming gets too far, the value is set to the minimum allowed value. If the range is going to below the range minimum, both ends of the axis are adjusted so that the range stays at the limit:

     if (m_axisXMinValue < m_areaMinValue)
         m_axisXMinValue = m_areaMinValue;
     if (m_axisXMaxValue > m_areaMaxValue)
         m_axisXMaxValue = m_areaMaxValue;
     // Don't allow too much zoom in
     if ((m_axisXMaxValue - m_axisXMinValue) < m_axisXMinRange) {
         float adjust = (m_axisXMinRange - (m_axisXMaxValue - m_axisXMinValue)) / 2.f;
         m_axisXMinValue -= adjust;
         m_axisXMaxValue += adjust;
     }

##### Highlight an Area of the Surface

To implement a highlight to be displayed on the surface, create a copy of the series and add some offset to the y value. In this example, the class `HighlightSeries` implements the creation of the copy in its `handlePositionChange` method.

First, give `HighlightSeries` the pointer to the original series, and then start listening to the QSurface3DSeries::selectedPointChanged signal:

     void HighlightSeries::setTopographicSeries(TopographicSeries *series)
     {
         m_topographicSeries = series;
         m_srcWidth = m_topographicSeries->dataArray().at(0).size();
         m_srcHeight = m_topographicSeries->dataArray().size();

         QObject::connect(m_topographicSeries,
                          &QSurface3DSeries::selectedPointChanged,
                          this,
                          &HighlightSeries::handlePositionChange);
     }

When the signal triggers, check that the position is valid. Then, calculate he ranges for the copied area, and check that they stay within the bounds. Finally, fill the data array of the highlight series with the range from the data array of the topography series:

     void HighlightSeries::handlePositionChange(const QPoint &position)
     {
         m_position = position;

         if (position == invalidSelectionPosition()) {
             setVisible(false);
             return;
         }

         int halfWidth = m_width / 2;
         int halfHeight = m_height / 2;

         int startX = position.x() - halfWidth;
         if (startX < 0)
             startX = 0;
         int endX = position.x() + halfWidth;
         if (endX > (m_srcWidth - 1))
             endX = m_srcWidth - 1;
         int startZ = position.y() - halfHeight;
         if (startZ < 0)
             startZ = 0;
         int endZ = position.y() + halfHeight;
         if (endZ > (m_srcHeight - 1))
             endZ = m_srcHeight - 1;

         const QSurfaceDataArray &srcArray = m_topographicSeries->dataArray();

         QSurfaceDataArray dataArray;
         dataArray.reserve(endZ - startZ);
         for (int i = startZ; i < endZ; ++i) {
             QSurfaceDataRow newRow;
             newRow.reserve(endX - startX);
             QSurfaceDataRow srcRow = srcArray.at(i);
             for (int j = startX; j < endX; ++j) {
                 QVector3D pos = srcRow.at(j).position();
                 pos.setY(pos.y() + m_heightAdjustment);
                 newRow.append(QSurfaceDataItem(pos));
             }
             dataArray.append(newRow);
         }

         dataProxy()->resetArray(dataArray);
         setVisible(true);
     }

##### A Gradient to the Highlight Series

Since the `HighlightSeries` is a QSurface3DSeries, all the decoration methods a series can have are available. In this example, add a gradient to emphasize the elevation. Because the suitable gradient style depends on the range of the Y axis and we change the range when zooming, the gradient color positions need to be adjusted as the range changes. Do this by defining proportional values for the gradient color positions:

     const float darkRedPos = 1.f;
     const float redPos = 0.8f;
     const float yellowPos = 0.6f;
     const float greenPos = 0.4f;
     const float darkGreenPos = 0.2f;

The gradient modification is done in the `handleGradientChange` method, so connect it to react to changes on the Y axis:

     QObject::connect(m_graph->axisY(),
                      &QValue3DAxis::maxChanged,
                      m_highlight,
                      &HighlightSeries::handleGradientChange);

When a change in the Y axis max value happens, calculate the new gradient color positions:

     void HighlightSeries::handleGradientChange(float value)
     {
         float ratio = m_minHeight / value;

         QLinearGradient gr;
         gr.setColorAt(0.f, Qt::black);
         gr.setColorAt(darkGreenPos * ratio, Qt::darkGreen);
         gr.setColorAt(greenPos * ratio, Qt::green);
         gr.setColorAt(yellowPos * ratio, Qt::yellow);
         gr.setColorAt(redPos * ratio, Qt::red);
         gr.setColorAt(darkRedPos * ratio, Qt::darkRed);

         setBaseGradient(gr);
         setColorStyle(QGraphsTheme::ColorStyle::RangeGradient);

         handleZoomChange(ratio);
     }

#### Example Contents

Example project @ code.qt.io