c++ - QChartView 和 QScatterSeries 覆盖了 QPointF 的标签

Question

我有一个 QChartView，它显示一些 2D 点，每个点代表一个特定项目 我想用项目名称标记每个点，而不是用它的 x、y 坐标作为默认行为

有什么方法可以实现覆盖创建或渲染标签的功能？

Answer 1

为什么在不更改 Qt 源代码的情况下很难实现这一点

1. QXYSeries::setPointLabelsFormat对你帮助不大。它确实允许您更改标签的格式，但它唯一可变的部分是点的坐标。

2. 所有的绘图都是在Qt类的私有(private)部分完成的。这是整个故事:

标签绘制在 private part 中QXYSeries (painter->drawText(position, pointLabel);):

void QXYSeriesPrivate::drawSeriesPointLabels(QPainter *painter, const QVector<QPointF> &points,
                                             const int offset)
{
    if (points.size() == 0)
        return;
    static const QString xPointTag(QLatin1String("@xPoint"));
    static const QString yPointTag(QLatin1String("@yPoint"));
    const int labelOffset = offset + 2;
    painter->setFont(m_pointLabelsFont);
    painter->setPen(QPen(m_pointLabelsColor));
    QFontMetrics fm(painter->font());
    // m_points is used for the label here as it has the series point information
    // points variable passed is used for positioning because it has the coordinates
    const int pointCount = qMin(points.size(), m_points.size());
    for (int i(0); i < pointCount; i++) {
        QString pointLabel = m_pointLabelsFormat;
        pointLabel.replace(xPointTag, presenter()->numberToString(m_points.at(i).x()));
        pointLabel.replace(yPointTag, presenter()->numberToString(m_points.at(i).y()));
        // Position text in relation to the point
        int pointLabelWidth = fm.width(pointLabel);
        QPointF position(points.at(i));
        position.setX(position.x() - pointLabelWidth / 2);
        position.setY(position.y() - labelOffset);
        painter->drawText(position, pointLabel);
    }
}

drawSeriesPointLabels 从 paint method 调用ScatterChartItem(该类未包含在官方文档中):

void ScatterChartItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    Q_UNUSED(option)
    Q_UNUSED(widget)
    if (m_series->useOpenGL())
        return;
    QRectF clipRect = QRectF(QPointF(0, 0), domain()->size());
    painter->save();
    painter->setClipRect(clipRect);
    if (m_pointLabelsVisible) {
        if (m_pointLabelsClipping)
            painter->setClipping(true);
        else
            painter->setClipping(false);
        m_series->d_func()->drawSeriesPointLabels(painter, m_points,
                                                  m_series->markerSize() / 2
                                                  + m_series->pen().width());
    }
    painter->restore();
}

ScatterChartItem 又是在 private part 中创建的QScatterSeries 并且不能用自定义类替换:

void QScatterSeriesPrivate::initializeGraphics(QGraphicsItem* parent)
{
    Q_Q(QScatterSeries);
    ScatterChartItem *scatter = new ScatterChartItem(q,parent);
    m_item.reset(scatter);
    QAbstractSeriesPrivate::initializeGraphics(parent);
}

你可能想尝试什么

1. 用setPointLabelsVisible(false);隐藏原来的标签，之后标签会单独绘制。

2. 子类 QChartView 并重新实现 paintEvent，首先调用 QChartView::paintEvent 然后调用自定义函数(比如说 drawCustomLabels)，它是 QXYSeriesPrivate::drawSeriesPointLabels 的修改版本。通过调用 drawCustomLabels 传递:

   • 本地画家在 MyChartView 的视口(viewport)上作画，
   • QXYSeries::points 返回的点，
   • 所需的偏移量。

下面是 drawCustomLabels 的示例:

void MyChartView::drawCustomLabels(QPainter *painter, const QVector<QPointF> &points, const int offset)
{
    if (points.count() == 0)
        return;

    QFontMetrics fm(painter->font());
    const int labelOffset = offset + 2;

    painter->setFont(m_pointLabelsFont); // Use QXYSeries::pointLabelsFont() to access m_pointLabelsFont
    painter->setPen(QPen(m_pointLabelsColor)); // Use QXYSeries::pointLabelsColor() to access m_pointLabelsColor

    for (int n(0); n < points.count(); n++) {
        QString pointLabel = "..."; // Set the desired label for the n-th point of the series
        // Position text in relation to the point
        int pointLabelWidth = fm.width(pointLabel);
        QPointF position(points.at(n));
        position.setX(position.x() - pointLabelWidth / 2);
        position.setY(position.y() - labelOffset);
        painter->drawText(position, pointLabel);
    }
}