arrow.h Example File

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  #ifndef ARROW_H
  #define ARROW_H

  #include <QGraphicsLineItem>

  #include "diagramitem.h"

  class QGraphicsPolygonItem;
  class QGraphicsLineItem;
  class QGraphicsScene;
  class QRectF;
  class QGraphicsSceneMouseEvent;
  class QPainterPath;

  class Arrow : public QGraphicsLineItem
  {
  public:
      enum { Type = UserType + 4 };

      Arrow(DiagramItem *startItem, DiagramItem *endItem,
        QGraphicsItem *parent = 0);

      int type() const override { return Type; }
      QRectF boundingRect() const override;
      QPainterPath shape() const override;
      void setColor(const QColor &color) { myColor = color; }
      DiagramItem *startItem() const { return myStartItem; }
      DiagramItem *endItem() const { return myEndItem; }

      void updatePosition();

  protected:
      void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = 0) override;

  private:
      DiagramItem *myStartItem;
      DiagramItem *myEndItem;
      QColor myColor;
      QPolygonF arrowHead;
  };

  #endif // ARROW_H