Qt官方示例-图表标注

❝本示例演示如何在图表中绘制一个附加元素(标注)。 ❞

标注核心要点：QChart类提供了两种方法来映射场景坐标和系列域(由坐标轴范围定义)。

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QPointF QChart::mapToPosition(const QPointF &value, QAbstractSeries *series)
QPointF QChart::mapToValue(const QPointF &position, QAbstractSeries *series)

核心代码：

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void Callout::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    Q_UNUSED(option)
    Q_UNUSED(widget)
    QPainterPath path;
    path.addRoundedRect(m_rect, 5, 5);

    QPointF anchor = mapFromParent(m_chart->mapToPosition(m_anchor)); // 映射坐标
    if (!m_rect.contains(anchor)) {
        QPointF point1, point2;

        // establish the position of the anchor point in relation to m_rect
        bool above = anchor.y() <= m_rect.top();
        bool aboveCenter = anchor.y() > m_rect.top() && anchor.y() <= m_rect.center().y();
        bool belowCenter = anchor.y() > m_rect.center().y() && anchor.y() <= m_rect.bottom();
        bool below = anchor.y() > m_rect.bottom();

        bool onLeft = anchor.x() <= m_rect.left();
        bool leftOfCenter = anchor.x() > m_rect.left() && anchor.x() <= m_rect.center().x();
        bool rightOfCenter = anchor.x() > m_rect.center().x() && anchor.x() <= m_rect.right();
        bool onRight = anchor.x() > m_rect.right();

        // get the nearest m_rect corner.
        qreal x = (onRight   rightOfCenter) * m_rect.width();
        qreal y = (below   belowCenter) * m_rect.height();
        bool cornerCase = (above && onLeft) || (above && onRight) || (below && onLeft) || (below && onRight);
        bool vertical = qAbs(anchor.x() - x) > qAbs(anchor.y() - y);

        qreal x1 = x   leftOfCenter * 10 - rightOfCenter * 20   cornerCase * !vertical * (onLeft * 10 - onRight * 20);
        qreal y1 = y   aboveCenter * 10 - belowCenter * 20   cornerCase * vertical * (above * 10 - below * 20);;
        point1.setX(x1);
        point1.setY(y1);

        qreal x2 = x   leftOfCenter * 20 - rightOfCenter * 10   cornerCase * !vertical * (onLeft * 20 - onRight * 10);;
        qreal y2 = y   aboveCenter * 20 - belowCenter * 10   cornerCase * vertical * (above * 20 - below * 10);;
        point2.setX(x2);
        point2.setY(y2);

        path.moveTo(point1);
        path.lineTo(anchor);
        path.lineTo(point2);
        path = path.simplified();
    }
    painter->setBrush(QColor(255, 255, 255));
    painter->drawPath(path);
    painter->drawText(m_textRect, m_text);
}

关于更多

在「QtCreator软件」可以找到：

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C:Qt{你的Qt版本}Examples{你的Qt版本}chartscallout

「相关链接」

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https://doc.qt.io/qt-5/qtcharts-callout-example.html

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