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# edge.cpp Example File
graphicsview/elasticnodes/edge.cpp

        /****************************************************************************
        **
        ** Copyright (C) 2006-2006 Trolltech ASA. All rights reserved.
        **
        ** This file is part of the example classes of the Qt Toolkit.
        **
        ** Licensees holding valid Qt Preview licenses may use this file in
        ** accordance with the Qt Preview License Agreement provided with the
        ** Software.
        **
        ** See http://www.trolltech.com/pricing.html or email sales@trolltech.com for
        ** information about Qt Commercial License Agreements.
        **
        ** Contact info@trolltech.com if any conditions of this licensing are
        ** not clear to you.
        **
        ** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
        ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        **
        ****************************************************************************/

        #include <QPainter>

        #include "edge.h"
        #include "node.h"

        #include <cmath>

        static const double Pi = 3.14159265358979323846264338327950288419717;
        static double TwoPi = 2.0 * Pi;

        Edge::Edge(Node *sourceNode, Node *destNode)
            : arrowSize(10)
        {
            setAcceptedMouseButtons(0);
            source = sourceNode;
            dest = destNode;
            source->addEdge(this);
            dest->addEdge(this);
            adjust();
        }

        Edge::~Edge()
        {
        }

        Node *Edge::sourceNode() const
        {
            return source;
        }

        void Edge::setSourceNode(Node *node)
        {
            source = node;
            adjust();
        }

        Node *Edge::destNode() const
        {
            return dest;
        }

        void Edge::setDestNode(Node *node)
        {
            dest = node;
            adjust();
        }

        void Edge::adjust()
        {
            if (!source || !dest)
                return;

            QLineF line(mapFromItem(source, 0, 0), mapFromItem(dest, 0, 0));
            qreal length = line.length();
            QPointF edgeOffset((line.dx() * 10) / length, (line.dy() * 10) / length);

            removeFromIndex();
            sourcePoint = line.p1() + edgeOffset;
            destPoint = line.p2() - edgeOffset;
            addToIndex();
        }

        QRectF Edge::boundingRect() const
        {
            if (!source || !dest)
                return QRectF();

            qreal penWidth = 1;
            qreal extra = (penWidth + arrowSize) / 2.0;

            return QRectF(sourcePoint, QSizeF(destPoint.x() - sourcePoint.x(),
                                              destPoint.y() - sourcePoint.y()))
                .normalized()
                .adjusted(-extra, -extra, extra, extra);
        }

        void Edge::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
        {
            if (!source || !dest)
                return;

            // Draw the line itself
            QLineF line(sourcePoint, destPoint);
            painter->setPen(QPen(Qt::black, 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
            painter->drawLine(line);

            // Draw the arrows if there's enough room
            double angle = ::acos(line.dx() / line.length());
            if (line.dy() >= 0)
                angle = TwoPi - angle;

            QPointF sourceArrowP1 = sourcePoint + QPointF(sin(angle + Pi / 3) * arrowSize,
                                                          cos(angle + Pi / 3) * arrowSize);
            QPointF sourceArrowP2 = sourcePoint + QPointF(sin(angle + Pi - Pi / 3) * arrowSize,
                                                          cos(angle + Pi - Pi / 3) * arrowSize);
            QPointF destArrowP1 = destPoint + QPointF(sin(angle - Pi / 3) * arrowSize,
                                                      cos(angle - Pi / 3) * arrowSize);
            QPointF destArrowP2 = destPoint + QPointF(sin(angle - Pi + Pi / 3) * arrowSize,
                                                      cos(angle - Pi + Pi / 3) * arrowSize);

            painter->setBrush(Qt::black);
            painter->drawPolygon(QPolygonF() << line.p1() << sourceArrowP1 << sourceArrowP2);
            painter->drawPolygon(QPolygonF() << line.p2() << destArrowP1 << destArrowP2);
        }