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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 <math.h>

    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);
    }