Graph Drawings with One Bend and Few Slopes

Abstract

We consider drawings of graphs in the plane in which edges are represented by polygonal paths with at most one bend and the number of different slopes used by all segments of these paths is small. We prove that \(\lceil \frac{\varDelta }{2}\rceil \) edge slopes suffice for outerplanar drawings of outerplanar graphs with maximum degree \(\varDelta \geqslant 3\). This matches the obvious lower bound. We also show that \(\lceil \frac{\varDelta }{2}\rceil +1\) edge slopes suffice for drawings of general graphs, improving on the previous bound of \(\varDelta +1\). Furthermore, we improve previous upper bounds on the number of slopes needed for planar drawings of planar and bipartite planar graphs.