arrow.h

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#ifndef ARROW_H
#define ARROW_H

#include <QGraphicsLineItem>

#include "diagramitem.h"

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

//! [0]
// The Arrow class is a graphics item that connects two DiagramItems. It draws an arrow head to one of the items. To achieve this the item needs to paint itself and also re implement methods used by the graphics scene to check for collisions and selections. The class inherits QGraphicsLine item, and draws the arrowhead and moves with the items it connects.
// The item's color can be set with setColor().
// boundingRect() and shape() are reimplemented from QGraphicsLineItem and are used by the scene to check for collisions and selections.
// Calling updatePosition() causes the arrow to recalculate its position and arrow head angle. paint() is reimplemented so that we can paint an arrow rather than just a line between items.
// myStartItem and myEndItem are the diagram items that the arrow connects. The arrow is drawn with its head to the end item. arrowHead is a polygon with three vertices's we use to draw the arrow head.
class Arrow : public QGraphicsLineItem
{
public:
    enum { Type = UserType + 4 };

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

    int type() const Q_DECL_OVERRIDE { return Type; }
    QRectF boundingRect() const Q_DECL_OVERRIDE;
    QPainterPath shape() const Q_DECL_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) Q_DECL_OVERRIDE;

private:
    DiagramItem *myStartItem;
    DiagramItem *myEndItem;
    QColor myColor;
    QPolygonF arrowHead;
};
//! [0]

#endif // ARROW_H