/// <summary>Compares two edges by the x-coordinates of the centers of their target nodes.</summary>
/// <param name="edge1">the first edge</param>
/// <param name="edge2">the second edge</param>
/// <returns>a negative value if the first target node is left of the second target node, a positive value if it's the
/// other way round and <c>0</c> if both target nodes are at the same x-coordinate</returns>
public virtual int Compare(object edge1, object edge2)
{
Node va = ((Edge)edge1).Target;
Node vb = ((Edge)edge2).Target;
LayoutGraph graph = (LayoutGraph)va.Graph;
return((int)((100.0 * (graph.GetCenterX(va) - graph.GetCenterX(vb)))));
}