Drawing Partial 2-Trees with Few Slopes

The planar slope number of a planar graph G is the minimum integer k such that G admits a planar drawing with vertices as points and edges as straight-line segments with k distinct slopes. Similarly, a plane slope number is defined for a plane graph, where a fixed combinatorial embedding of the graph is given and the output must respect the given embedding. We prove tight bounds (up to a small multiplicative or additive constant) for the plane and the planar slope numbers of partial 2-trees of bounded degree. We also answer a long standing question by Garg and Tamassia (In: van Leeuwen J (eds) Proceedings of the Second Annual European Symposium on Algorithms (ESA), LNCS, vol 855, pp 12-23, Springer, 1994) on the angular resolution of the planar straight-line drawings of series-parallel graphs of bounded degree.