callout.cpp Example File

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  ** Copyright (C) 2016 The Qt Company Ltd.
  ** Contact: https://www.qt.io/licensing/
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  ** This file is part of the Qt Charts module of the Qt Toolkit.
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  #include "callout.h"
  #include <QtGui/QPainter>
  #include <QtGui/QFontMetrics>
  #include <QtWidgets/QGraphicsSceneMouseEvent>
  #include <QtGui/QMouseEvent>
  #include <QtCharts/QChart>

  Callout::Callout(QChart *chart):
      QGraphicsItem(chart),
      m_chart(chart)
  {
  }

  QRectF Callout::boundingRect() const
  {
      QPointF anchor = mapFromParent(m_chart->mapToPosition(m_anchor));
      QRectF rect;
      rect.setLeft(qMin(m_rect.left(), anchor.x()));
      rect.setRight(qMax(m_rect.right(), anchor.x()));
      rect.setTop(qMin(m_rect.top(), anchor.y()));
      rect.setBottom(qMax(m_rect.bottom(), anchor.y()));
      return rect;
  }

  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));
      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);
  }

  void Callout::mousePressEvent(QGraphicsSceneMouseEvent *event)
  {
      event->setAccepted(true);
  }

  void Callout::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
  {
      if (event->buttons() & Qt::LeftButton){
          setPos(mapToParent(event->pos() - event->buttonDownPos(Qt::LeftButton)));
          event->setAccepted(true);
      } else {
          event->setAccepted(false);
      }
  }

  void Callout::setText(const QString &text)
  {
      m_text = text;
      QFontMetrics metrics(m_font);
      m_textRect = metrics.boundingRect(QRect(0, 0, 150, 150), Qt::AlignLeft, m_text);
      m_textRect.translate(5, 5);
      prepareGeometryChange();
      m_rect = m_textRect.adjusted(-5, -5, 5, 5);
  }

  void Callout::setAnchor(QPointF point)
  {
      m_anchor = point;
  }

  void Callout::updateGeometry()
  {
      prepareGeometryChange();
      setPos(m_chart->mapToPosition(m_anchor) + QPoint(10, -50));
  }