,
Susanna Caroppo
,
Giordano Da Lozzo
,
Marco D'Elia
,
Giuseppe Di Battista
,
Fabrizio Frati
,
Fabrizio Grosso
,
Maurizio Patrignani
Creative Commons Attribution 4.0 International license
The Partial Drawing Extensibility problem, for short PDE, takes as input a triple ⟨ G,H,Γ_H⟩, where G is a planar graph, H is a subgraph of G, and Γ_H is a straight-line planar drawing of H, and asks whether Γ_H can be extended to a straight-line planar drawing of G. Patrignani [Int. J. Found. Comput. Sci. (2006)] proved that the PDE problem is NP-hard, exploiting instances in which H is highly disconnected. In this paper, we study the PDE problem under the requirement that the initial partial drawing Γ_H is biconnected. We show that PDE remains NP-hard even for instances in which H is a biconnected graph with faces of bounded size, G is subcubic, and the part of G that is not in H consists of length-2 paths. The complexity of PDE remains however open when H is connected (or even biconnected) if G has a fixed embedding. In this setting both a polynomial-time algorithm or an NP-hardness proof seem to be elusive targets. As a step towards tackling this problem, we study instances of PDE in which H is biconnected, G has a fixed embedding, and the rest of the graph consists of p length-2 paths, and present an O(p² n)-time algorithm, a result in sharp contrast with the NP-hardness of the variable embedding setting. Moreover, with an approach based on the Existential Theory of the Reals, we show that, if H is biconnected, the problem is FPT parameterized by the vertex cover number of G, both in a fixed and in a variable embedding setting.
@InProceedings{andreola_et_al:LIPIcs.GD.2026.4,
author = {Andreola, Giordano and Caroppo, Susanna and Da Lozzo, Giordano and D'Elia, Marco and Di Battista, Giuseppe and Frati, Fabrizio and Grosso, Fabrizio and Patrignani, Maurizio},
title = {{Extending Biconnected Straight-Line Planar Drawings}},
booktitle = {34th International Symposium on Graph Drawing and Network Visualization (GD 2026)},
pages = {4:1--4:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-452-9},
ISSN = {1868-8969},
year = {2026},
volume = {396},
editor = {L\"{o}ffler, Maarten and Miksch, Silvia},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.GD.2026.4},
URN = {urn:nbn:de:0030-drops-278995},
doi = {10.4230/LIPIcs.GD.2026.4},
annote = {Keywords: Planar Graphs, Straight-line Drawings, Extension Problems, FPT, Fixed Embedding}
}