edge.cpp Example File

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

  #include <math.h>

  #include <QPainter>

  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();
  }

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

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

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

      QLineF line(mapFromItem(source, 0, 0), mapFromItem(dest, 0, 0));
      qreal length = line.length();

      prepareGeometryChange();

      if (length > qreal(20.)) {
          QPointF edgeOffset((line.dx() * 10) / length, (line.dy() * 10) / length);
          sourcePoint = line.p1() + edgeOffset;
          destPoint = line.p2() - edgeOffset;
      } else {
          sourcePoint = destPoint = line.p1();
      }
  }

  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;

      QLineF line(sourcePoint, destPoint);
      if (qFuzzyCompare(line.length(), qreal(0.)))
          return;

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

      // Draw the arrows
      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);
  }