Re: graphs (layouting-related)

• To: Manuel Simoni <manuels@xxxxxxxxxxxxxxxxxxxxx>
• Subject: Re: graphs (layouting-related)
• From: Oscar Stiffelman <oscar@xxxxxxxxxxxx>
• Date: Fri, 25 Jan 2002 19:18:26 -0800 (PST)

The approach sounds interesting, but I would definitely not make that part
of the java interface for the graph layout.  You should provide a very
"thin" api for doing the layout, possibly just a single signature of the
form:

public interface ILayoutAlgorithm {
  public void doLayout(IGraph graph, ICoordinates coords) throws
                                                LayoutException;
}

Where the coordinates are pre-allocated to the size of the graph.  Or do
what swing does for performance reasons and make it return a new one only
if the param version is invalid or null.


Then if you want to construct what you describe, you could make a class
that implements ILayoutAlgorithm using a collection of nested layout
algorithms and weights.

But there are so many different kinds of layout algorithms that I would
not assume any more than the above interface.

Notice taht I made the graph an interface as well because there are
definitely very different implementations that will need to be supported
(sparse/dense).

 -- Oscar

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On Fri, 25 Jan 2002, Manuel Simoni wrote:

> Oscar,
>
> > I am not a visad expert, but I recommend not coupling the graph (adjacency
> > matrix or adjacency list) data structure to the existing VisAD data
> > structures, until it comes time for the embedding in R^2 or R^3 (which is
> > the function performed by the layout algorithm).  It will be easier for
> > people to import graph data into whatever you design if you keep the
> > topology encoding and the cartesian embedding conceptually orthogonal to
> > each other.
>
> Yes, that's exactly what I am after. I am especially interested in the
> combination of multiple layout algorithms in one graph, but I do not have
> experience with that yet.
>
> Possibly this could be achieved by defining a strength or weight for each
> layout-algorithm at runtime, so that a higher-weight algorithm overrides the
> lower ones.
>
> This approach is used in the cassowary constraint solver - it also uses the
> metaphor of suggestion: The user (or a layout mechanism ) can *suggest* new
> positions for nodes of the graph, but cannot assume that the changes make it
> thru (for example, if the new position of the node would conflict with a
> constraint or another layout mechanism.)
>
> Manuel
>
>
>

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