Question

Im looking to implement an application that is working with and displaying simple graph. One of those is a tree, one is like an automaton.

I decided to use OGDF in addition to Qt, because i need layouting. But Im not quite getting this…do I have to to implement all the drawing/positioning functionality myself (like fetching all the node and edge coordinates from GraphAttributes) or does OGDF provide some nice interface for that? (as nice as GraphAttributes::writeGML())

Answer 1

I couldn’t find any nice interface so I am just fetching the coordinates myself, however, this approach is not perfect since the layout algorithm returns negative coordinates (relative to a graph center point I think, instead of the normal topleft origin). My code looks kinda like this:

int nodeWidth = 30, nodeHeight = 30, siblingDistance = nodeWidth + nodeHeight;

ogdf::TreeLayout treeLayout;
treeLayout.siblingDistance(siblingDistance);
treeLayout.call(GA);

int width = GA.boundingBox().width(), height = GA.boundingBox().height();

ui->graphView->scene()->setSceneRect(QRect(0, 0, width+nodeWidth, height+nodeHeight));
cout << "Scene dimensions: " << GA.boundingBox().width() << " x " << GA.boundingBox().height() << endl;

GA.setAllWidth(nodeWidth);
GA.setAllHeight(nodeHeight);

ogdf::edge e;
forall_edges(e,graph){
    ogdf::node source = e->source(), target = e->target();
    int x1 = GA.x(source), y1 = GA.y(source);
    int x2 = GA.x(target), y2 = GA.y(target);
    QPainterPath p;
    p.moveTo(x1 + nodeWidth/2, y1 + nodeHeight/2);
    p.lineTo(x2 + nodeWidth/2, y2 + nodeHeight/2);
    (void) ui->graphView->scene()->addPath(p, QPen(Qt::darkGray), QBrush(Qt::white));
}

ogdf::node n;
forall_nodes(n, graph) {
    double x = GA.x(n);
    double y = GA.y(n);
    double w = GA.width(n);
    double h = GA.height(n);
    QRectF boundingRect(x, y, w, h);
    cout << x << " : " << y << " : " << endl;
    QRadialGradient radialGradient(boundingRect.center(), boundingRect.width());
    radialGradient.setColorAt(1.0, Qt::lightGray);
    radialGradient.setColorAt(0.7, QColor(230,230,240));
    radialGradient.setColorAt(0.0, Qt::white);
    (void) ui->graphView->scene()->addEllipse(boundingRect, QPen(Qt::black), QBrush(QRadialGradient(radialGradient)));
    QGraphicsTextItem *text = ui->graphView->scene()->addText(QString(GA.labelNode(n).cstr()));
    text->setPos(x, y);
}

// clear the graph after it has been displayed
graph.clear();