arrow.cpp Example File

 /****************************************************************************
 **
 ** Copyright (C) 2015 The Qt Company Ltd.
 ** Contact: http://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** You may use this file under the terms of the BSD license as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of The Qt Company Ltd nor the names of its
 **     contributors may be used to endorse or promote products derived
 **     from this software without specific prior written permission.
 **
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #include <QtGui>

 #include "arrow.h"
 #include <math.h>

 const qreal Pi = 3.14;

 Arrow::Arrow(DiagramItem *startItem, DiagramItem *endItem,
          QGraphicsItem *parent, QGraphicsScene *scene)
     : QGraphicsLineItem(parent, scene)
 {
     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 = ::acos(line().dx() / line().length());
     if (line().dy() >= 0)
         angle = (Pi * 2) - angle;

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