public IEnumerable <int> Build(IEnumerable <Vector2> vertices, IReadOnlyCollection <IEnumerable <int> > holeVertices)
{
var sortedVertices = vertices.Select((v, index) => new SortedVertex(index, v))
.OrderBy(v => v.Vertex.x).ThenBy(v => v.Vertex.y).ToList();
if (sortedVertices.Count < 3)
{
throw new ArgumentException($"Minimum vertices count for triangulation is 3, but was {sortedVertices.Count}");
}
var convexHull = new HullEdgesList(sortedVertices.Count);
var graph = new TriangulationGraph();
convexHull.Add(new HullEdge(1, 1));
convexHull.Add(new HullEdge(0, 0));
graph[new Edge(0, 1)].Insert(2);
for (var i = 2; i < sortedVertices.Count; i++)
{
AddVertexToTriangulation(i, sortedVertices, convexHull, graph);
}
return(DelaunayTriangulationConverter.ConvertToTriangulation(graph, sortedVertices, holeVertices));
}
private static int FixTriangulationIteratively(int vertexId, List <SortedVertex> vertices, HullEdgesList convexHull, HullEdge.IterationDirections direction,
Func <Vector2, Vector2, bool> condition, Action <int, int, int> fixTriangulation)
{
var iterationsCount = 0;
const int maxIterationsCount = 100;
var hullVertex = vertexId - 1;
var lastVector = vertices[hullVertex].Vertex - vertices[vertexId].Vertex;
var nextHullVertex = convexHull[hullVertex].Get(direction);
var newVector = vertices[nextHullVertex].Vertex - vertices[vertexId].Vertex;
while (condition(lastVector, newVector) && iterationsCount < maxIterationsCount)
{
fixTriangulation(hullVertex, nextHullVertex, vertexId);
hullVertex = nextHullVertex;
lastVector = newVector;
nextHullVertex = convexHull[hullVertex].Get(direction);
newVector = vertices[nextHullVertex].Vertex - vertices[vertexId].Vertex;
iterationsCount++;
}
convexHull[vertexId].Set(direction, hullVertex);
return(hullVertex);
}
private static void AddVertexToTriangulation(int vertexId, List <SortedVertex> vertices, HullEdgesList convexHull,
TriangulationGraph graph)
{
FixTriangulationIteratively(vertexId, vertices, convexHull, HullEdge.IterationDirections.Right,
(v1, v2) => TriangulationHelper.CrossProduct(v1, v2) > -DelaunayTriangulationValidator.Eps,
(left, right, outer) => FixTriangulation(left, right, outer, vertices, graph));
var hullVertex = FixTriangulationIteratively(vertexId, vertices, convexHull, HullEdge.IterationDirections.Left,
(v1, v2) => TriangulationHelper.CrossProduct(v1, v2) < DelaunayTriangulationValidator.Eps,
(left, right, outer) => FixTriangulation(right, left, outer, vertices, graph));
convexHull[convexHull[vertexId].Right].Set(HullEdge.IterationDirections.Left, vertexId);
convexHull[hullVertex].Set(HullEdge.IterationDirections.Right, vertexId);
}
