public Edge(SimplifiedEdge e, int rightPoly)
{
P0 = e.P0;
P1 = e.P1;
IsBidirectional = false;
RightPoly = rightPoly;
}
// Note: allows output to have consecutive colinear edges in a partition
public DTMesh ExecuteToMesh(DTMesh input)
{
List <int> clearedPolys = new List <int>();
Dictionary <SimplifiedEdge, Edge> realEdges = new Dictionary <SimplifiedEdge, Edge>();
List <int>[] tempPartitions = new List <int> [input.Partitions.Count];
int[] polyRemapper = new int[input.Partitions.Count];
// Local function that gets the remapped polygon index for the given original index
int getRemappedIndex(int i)
{
Stack <int> collapseStack = new Stack <int>();
while (i != polyRemapper[i])
{
collapseStack.Push(i);
i = polyRemapper[i];
}
// Lazily collapse remapping chains (entries that remap multiple times should remap only once)
while (collapseStack.Count > 0)
{
polyRemapper[collapseStack.Pop()] = i;
}
return(i);
}
// Determine internal edges and map them to their connected polygons
for (int polyIndex = 0; polyIndex < input.Partitions.Count; polyIndex++)
{
List <int> poly = input.Partitions[polyIndex];
tempPartitions[polyIndex] = new List <int>(poly);
polyRemapper[polyIndex] = polyIndex;
// Add all the initial partitions (triangles if the input was a triangulation)
for (int vertexIndex = 0; vertexIndex < poly.Count; vertexIndex++)
{
int v = poly[vertexIndex];
int vNext = poly.GetCircular(vertexIndex + 1);
SimplifiedEdge e = new SimplifiedEdge(v, vNext);
if (!realEdges.ContainsKey(e))
{
// If this is the first time visiting this edge, make a new entry and add the right polygon
realEdges[e] = new Edge(e, polyIndex);
}
else
{
// If we have already visited this edge, add the left polygon and make the edge bidirectional
realEdges[e].IsBidirectional = true;
realEdges[e].LeftPoly = polyIndex;
}
}
}
// Iterate internal edges and check if they can be removed without creating concave partitions
foreach (var internalEdgePair in realEdges.Where(edgePair => edgePair.Value.IsBidirectional))
{
SimplifiedEdge simpleEdge = internalEdgePair.Key;
Edge realEdge = internalEdgePair.Value;
// Find the index within the right polygon where the shared edge ends (P1)
int rightPolyIndex = getRemappedIndex(realEdge.RightPoly);
List <int> rightPoly = tempPartitions[rightPolyIndex];
int rightPolyStart = -1;
for (int i = 0; i < rightPoly.Count; i++)
{
int p = rightPoly[i];
if (p == simpleEdge.P1)
{
rightPolyStart = i;
break;
}
}
// Find the index within the left polygon where the shared edge ends (P0)
int leftPolyIndex = getRemappedIndex(realEdge.LeftPoly);
List <int> leftPoly = tempPartitions[leftPolyIndex];
int leftPolyStart = -1;
for (int i = 0; i < leftPoly.Count; i++)
{
int p = leftPoly[i];
if (p == simpleEdge.P0)
{
leftPolyStart = i;
break;
}
}
// Determine if the angle at the edge's P0 would become reflex if this edge were removed
Vector2 rightPolyLastEdge = input.Vertices[rightPoly.GetCircular(rightPolyStart - 1)] - input.Vertices[rightPoly.GetCircular(rightPolyStart - 2)];
Vector2 leftPolyFirstEdge = input.Vertices[leftPoly.GetCircular(leftPolyStart + 1)] - input.Vertices[leftPoly.GetCircular(leftPolyStart)];
bool p0Reflex = Vector3.Cross(rightPolyLastEdge, leftPolyFirstEdge).z > 0;
// Determine if the angle at the edge's P1 would become reflex if this edge were removed
Vector2 leftPolyLastEdge = input.Vertices[leftPoly.GetCircular(leftPolyStart - 1)] - input.Vertices[leftPoly.GetCircular(leftPolyStart - 2)];
Vector2 rightPolyFirstEdge = input.Vertices[rightPoly.GetCircular(rightPolyStart + 1)] - input.Vertices[rightPoly.GetCircular(rightPolyStart)];
bool p1Reflex = Vector3.Cross(leftPolyLastEdge, rightPolyFirstEdge).z > 0;
if (!p0Reflex && !p1Reflex)
{
// Remove the edge and merge the two polygons since the result will be convex
// Add points from rightPoly in CW order from the removed edge's P1 to P0, including P1 but not P0
List <int> newPoly = rightPoly.GetRange(rightPolyStart, rightPoly.Count - rightPolyStart);
newPoly.AddRange(rightPoly.GetRange(0, rightPolyStart));
newPoly.RemoveAt(newPoly.Count - 1);
// Add points from left in CW order from the removed edge's P0 to P1, including P0 but not P1
newPoly.AddRange(leftPoly.GetRange(leftPolyStart, leftPoly.Count - leftPolyStart));
newPoly.AddRange(leftPoly.GetRange(0, leftPolyStart));
newPoly.RemoveAt(newPoly.Count - 1);
// Modify the right polygon
rightPoly.Clear();
rightPoly.AddRange(newPoly);
// Clear the left polygon
leftPoly.Clear();
clearedPolys.Add(leftPolyIndex);
// Remap the left polygon index to match the right
polyRemapper[leftPolyIndex] = rightPolyIndex;
}
}
// Return a new mesh that copies the vertices of the original, but uses the merged partitions
// (ignores the left partitions that we cleared)
return(new DTMesh(new List <Vector2>(input.Vertices),
tempPartitions.Where(partition => partition.Count > 0).ToList()));
}
