/// <summary>
/// Partitions a complex polygon (with chords and holes) into a group of chordless polygons.
/// </summary>
/// <param name="allIsoPerims">Array of lists of Vector2s, each describing a perimeter of a tile group.</param>
/// <returns>A list of lists of Vector2s, each list describing a chordless polygon.</returns>
// ReSharper disable once ReturnTypeCanBeEnumerable.Local
private static (List <Chord>, List <ChordlessPolygon>) _ComplexToChordlessPolygons(List <Vector2>[] allIsoPerims)
{
HashSet <ConcaveVertex> concaveVertices = ConcaveVertexFinder.GetConcaveVertices(allIsoPerims);
List <Chord> chords = _FindChords(concaveVertices, allIsoPerims);
Dictionary <BipartiteGraphNode, Chord> bipartiteNodeToChords = _ConvertChordsToNodes(chords);
var bipartiteGraph = new BipartiteGraph(bipartiteNodeToChords.Keys);
HashSet <BipartiteGraphNode> maxIndependentSet = bipartiteGraph.GetMaxIndependentSet();
List <PolygonSplittingGraphNode> polygonSplittingNodes = _ConstructPolygonSplittingNodes(allIsoPerims, bipartiteNodeToChords, maxIndependentSet);
var holes = new List <List <Vector2> >();
for (int i = 1; i < allIsoPerims.Length; i++)
{
holes.Add(allIsoPerims[i]);
}
var polygonSplittingGraph = new PolygonSplittingGraph(polygonSplittingNodes, holes);
List <ChordlessPolygon> minCycles = polygonSplittingGraph.GetMinCycles();
return(chords, minCycles);
}
/// <summary>
/// Splits a chordless polygon into rectangles by extending its concave vertices according to the following criteria:
/// 1. If the vertex has a bridge, extend in that direction.
/// 2. If possible to extend in a direction that forms a chord, do NOT do it.
/// 3. If neither of the above, either direction works.
/// This method then builds PolygonSplittingGraphNodes to make a PolygonSplittingGraph and then runs the GetMinCycles
/// func in order to get rectangles.
/// </summary>
/// <param name="chordlessPolygons">A list of chordless polygons.</param>
/// <returns>A list of lists of four vector2s, AKA a list of lists of rectangles.</returns>
public static List <List <Vector2> > DecomposeChordlessPolygonToRectangles(this List <ChordlessPolygon> chordlessPolygons,
List <Chord> chords)
{
if (chordlessPolygons is null)
{
throw new ArgumentNullException(nameof(chordlessPolygons));
}
var rectangles = new List <List <Vector2> >();
foreach (ChordlessPolygon polygon in chordlessPolygons)
{
HashSet <ConcaveVertex> concaveVertices = ConcaveVertexFinder.GetConcaveVertices(polygon);
List <PolyEdge> extensionSegments = _FindVertexExtensions(polygon, concaveVertices, chords);
HashSet <Vector2> extensionVertices = _GetNewVertices(polygon, extensionSegments);
(List <Vector2> newPerim, List <List <Vector2> > newHoles) = _InsertNewVerticesIntoPerims(polygon, extensionVertices);
List <PolygonSplittingGraphNode> nodes = _CreateNewNodes(newPerim, newHoles, extensionSegments);
var polygonSplittingGraph = new PolygonSplittingGraph(nodes, newHoles);
List <ChordlessPolygon> newRectangles = polygonSplittingGraph.GetMinCycles();
rectangles.AddRange(newRectangles.Select(rectangle => rectangle.outerPerim.ToList()));
}
return(rectangles);
}