node.cpp Example File

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

  #include <QGraphicsScene>
  #include <QGraphicsSceneMouseEvent>
  #include <QPainter>
  #include <QStyleOption>

  Node::Node(GraphWidget *graphWidget)
      : graph(graphWidget)
  {
      setFlag(ItemIsMovable);
      setFlag(ItemSendsGeometryChanges);
      setCacheMode(DeviceCoordinateCache);
      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;

          QPointF vec = mapToItem(node, 0, 0);
          qreal dx = vec.x();
          qreal dy = vec.y();
          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 vec;
          if (edge->sourceNode() == this)
              vec = mapToItem(edge->destNode(), 0, 0);
          else
              vec = mapToItem(edge->sourceNode(), 0, 0);
          xvel -= vec.x() / weight;
          yvel -= vec.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 ItemPositionHasChanged:
          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);
  }