Coordinate descent heuristics for the irregular strip packing problem of rasterized shapes

We consider the irregular strip packing problem of rasterized shapes, where a given set of pieces of irregular shapes represented in pixels should be placed into a rectangular container without overlap. The rasterized shapes enable us to check overlap without any exceptional handling due to geometric issues, while they often require much memory and computational effort in high-resolution. We develop an efficient algorithm to check overlap using a pair of scanlines that reduces the complexity of rasterized shapes by merging consecutive pixels in each row and column into strips with unit width, respectively. Based on this, we develop coordinate descent heuristics that repeat a line search in the horizontal and vertical directions alternately. Computational results for test instances show that the proposed algorithm obtains sufficiently dense layouts of rasterized shapes in high-resolution within a reasonable computation time.