Drawing with Fat Edges

In this paper, we introduce the problem of drawing with “fat” edges. Traditionally, graph drawing algorithms represent vertices as circles and edges as closed curves connecting the vertices. In this paper we consider the problem of drawing graphs with edges of variable thickness. The thickness of an edge is often used as a visualization cue, to indicate importance, or to convey some additional information. We present a model for drawing with fat edges and a corresponding polynomial time algorithm that uses the model. We focus on a restricted class of graphs that occur in VLSI wire routing and show how to extend the algorithm to general planar graphs. We show how to take an arbitrary wire routing and convert it into a homotopic equivalent routing such that the distance between any two wires is maximized. Moreover, the routing uses the minimum length wires. Maximizing the distance between wires is equivalent to finding the drawing in which the edges are drawn as thick as possible. To the best of our knowledge this is the first algorithm that finds the maximal distance between any two wires and allows for wires of variable thickness. The previous best known result for the corresponding decision problem with unit wire thickness is the algorithm of Gao et al., which runs in O(kn log(kn)) time and uses O(kn) space, where n is the number of wires and k is the maximum of the input and output complexities. The running time of our algorithm is O(kn+ n) and the space required is O(k + n). The algorithm generalizes naturally to general planar graphs as well. ⋆ This is a report of ongoing research. The full proofs and new results will be maintained in the full version of the paper, which is available at www.cs.arizona.edu/~alon/papers/fatedges.ps.gz ⋆⋆ Supported by Deutsche Forschungsgemeinschaft, grant AL 253/4-3.