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# node.cpp Example File
graphicsview/elasticnodes/node.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 <QGraphicsScene>
    #include <QGraphicsSceneMouseEvent>
    #include <QPainter>
    #include <QStyleOption>

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

    Node::Node(GraphWidget *graphWidget)
        : graph(graphWidget)
    {
        setFlag(ItemIsMovable);
        setZValue(1);
    }

    void Node::addEdge(Edge *edge)
    {
        edgeList << edge;
        edge->adjust();
    }

    QList<Edge *> Node::edges() const
    {
        return edgeList;
    }

    void Node::calculateForces()
    {
        if (!scene() || scene()->mouseGrabberItem() == this) {
            newPos = pos();
            return;
        }

        // Sum up all forces pushing this item away
        qreal xvel = 0;
        qreal yvel = 0;
        foreach (QGraphicsItem *item, scene()->items()) {
            Node *node = qgraphicsitem_cast<Node *>(item);
            if (!node)
                continue;

            QLineF line(mapFromItem(node, 0, 0), QPointF(0, 0));
            qreal dx = line.dx();
            qreal dy = line.dy();
            double l = 2.0 * (dx * dx + dy * dy);
            if (l > 0) {
                xvel += (dx * 150.0) / l;
                yvel += (dy * 150.0) / l;
            }
        }

        // Now subtract all forces pulling items together
        double weight = (edgeList.size() + 1) * 10;
        foreach (Edge *edge, edgeList) {
            QPointF pos;
            if (edge->sourceNode() == this)
                pos = mapFromItem(edge->destNode(), 0, 0);
            else
                pos = mapFromItem(edge->sourceNode(), 0, 0);
            xvel += pos.x() / weight;
            yvel += pos.y() / weight;
        }

        if (qAbs(xvel) < 0.1 && qAbs(yvel) < 0.1)
            xvel = yvel = 0;

        QRectF sceneRect = scene()->sceneRect();
        newPos = pos() + QPointF(xvel, yvel);
        newPos.setX(qMin(qMax(newPos.x(), sceneRect.left() + 10), sceneRect.right() - 10));
        newPos.setY(qMin(qMax(newPos.y(), sceneRect.top() + 10), sceneRect.bottom() - 10));
    }

    bool Node::advance()
    {
        if (newPos == pos())
            return false;

        setPos(newPos);
        return true;
    }

    QRectF Node::boundingRect() const
    {
        qreal adjust = 2;
        return QRectF(-10 - adjust, -10 - adjust,
                      23 + adjust, 23 + adjust);
    }

    QPainterPath Node::shape() const
    {
        QPainterPath path;
        path.addEllipse(-10, -10, 20, 20);
        return path;
    }

    void Node::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
    {
        painter->setPen(Qt::NoPen);
        painter->setBrush(Qt::darkGray);
        painter->drawEllipse(-7, -7, 20, 20);

        QRadialGradient gradient(-3, -3, 10);
        if (option->state & QStyle::State_Sunken) {
            gradient.setCenter(3, 3);
            gradient.setFocalPoint(3, 3);
            gradient.setColorAt(1, QColor(Qt::yellow).light(120));
            gradient.setColorAt(0, QColor(Qt::darkYellow).light(120));
        } else {
            gradient.setColorAt(0, Qt::yellow);
            gradient.setColorAt(1, Qt::darkYellow);
        }
        painter->setBrush(gradient);
        painter->setPen(QPen(Qt::black, 0));
        painter->drawEllipse(-10, -10, 20, 20);
    }

    QVariant Node::itemChange(GraphicsItemChange change, const QVariant &value)
    {
        switch (change) {
        case ItemPositionChange:
            foreach (Edge *edge, edgeList)
                edge->adjust();
            graph->itemMoved();
            break;
        default:
            break;
        };

        return QGraphicsItem::itemChange(change, value);
    }

    void Node::mousePressEvent(QGraphicsSceneMouseEvent *event)
    {
        update();
        QGraphicsItem::mousePressEvent(event);
    }

    void Node::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
    {
        update();
        QGraphicsItem::mouseReleaseEvent(event);
    }