arrow.cpp Example File

graphicsview/diagramscene/arrow.cpp
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 #include "arrow.h"

 #include <qmath.h>
 #include <QPen>
 #include <QPainter>

 Arrow::Arrow(DiagramItem *startItem, DiagramItem *endItem, QGraphicsItem *parent)
     : QGraphicsLineItem(parent)
 {
     myStartItem = startItem;
     myEndItem = endItem;
     setFlag(QGraphicsItem::ItemIsSelectable, true);
     myColor = Qt::black;
     setPen(QPen(myColor, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
 }

 QRectF Arrow::boundingRect() const
 {
     qreal extra = (pen().width() + 20) / 2.0;

     return QRectF(line().p1(), QSizeF(line().p2().x() - line().p1().x(),
                                       line().p2().y() - line().p1().y()))
         .normalized()
         .adjusted(-extra, -extra, extra, extra);
 }

 QPainterPath Arrow::shape() const
 {
     QPainterPath path = QGraphicsLineItem::shape();
     path.addPolygon(arrowHead);
     return path;
 }

 void Arrow::updatePosition()
 {
     QLineF line(mapFromItem(myStartItem, 0, 0), mapFromItem(myEndItem, 0, 0));
     setLine(line);
 }

 void Arrow::paint(QPainter *painter, const QStyleOptionGraphicsItem *,
           QWidget *)
 {
     if (myStartItem->collidesWithItem(myEndItem))
         return;

     QPen myPen = pen();
     myPen.setColor(myColor);
     qreal arrowSize = 20;
     painter->setPen(myPen);
     painter->setBrush(myColor);

     QLineF centerLine(myStartItem->pos(), myEndItem->pos());
     QPolygonF endPolygon = myEndItem->polygon();
     QPointF p1 = endPolygon.first() + myEndItem->pos();
     QPointF p2;
     QPointF intersectPoint;
     QLineF polyLine;
     for (int i = 1; i < endPolygon.count(); ++i) {
         p2 = endPolygon.at(i) + myEndItem->pos();
         polyLine = QLineF(p1, p2);
         QLineF::IntersectType intersectType =
             polyLine.intersect(centerLine, &intersectPoint);
         if (intersectType == QLineF::BoundedIntersection)
             break;
         p1 = p2;
     }

     setLine(QLineF(intersectPoint, myStartItem->pos()));

     double angle = std::atan2(-line().dy(), line().dx());

     QPointF arrowP1 = line().p1() + QPointF(sin(angle + M_PI / 3) * arrowSize,
                                     cos(angle + M_PI / 3) * arrowSize);
     QPointF arrowP2 = line().p1() + QPointF(sin(angle + M_PI - M_PI / 3) * arrowSize,
                                     cos(angle + M_PI - M_PI / 3) * arrowSize);

     arrowHead.clear();
     arrowHead << line().p1() << arrowP1 << arrowP2;
     painter->drawLine(line());
     painter->drawPolygon(arrowHead);
     if (isSelected()) {
         painter->setPen(QPen(myColor, 1, Qt::DashLine));
         QLineF myLine = line();
         myLine.translate(0, 4.0);
         painter->drawLine(myLine);
         myLine.translate(0,-8.0);
         painter->drawLine(myLine);
     }
 }