// From Eric Jordan's convex decomposition library
/// <summary>
/// Trace the edge of a non-simple polygon and return a simple polygon.
///
/// Method:
/// Start at vertex with minimum y (pick maximum x one if there are two).
/// We aim our "lastDir" vector at (1.0, 0)
/// We look at the two rays going off from our start vertex, and follow whichever
/// has the smallest angle (in -Pi . Pi) wrt lastDir ("rightest" turn)
/// Loop until we hit starting vertex:
/// We add our current vertex to the list.
/// We check the seg from current vertex to next vertex for intersections
/// - if no intersections, follow to next vertex and continue
/// - if intersections, pick one with minimum distance
/// - if more than one, pick one with "rightest" next point (two possibilities for each)
/// </summary>
/// <param name="verts">The vertices.</param>
public Vertices TraceEdge(Vertices verts)
{
PolyNode[] nodes = new PolyNode[verts.Count * verts.Count];
//overkill, but sufficient (order of mag. is right)
int nNodes = 0;
//Add base nodes (raw outline)
for (int i = 0; i < verts.Count; ++i)
{
Vector2 pos = new Vector2(verts[i].X, verts[i].Y);
nodes[i].Position = pos;
++nNodes;
int iplus = (i == verts.Count - 1) ? 0 : i + 1;
int iminus = (i == 0) ? verts.Count - 1 : i - 1;
nodes[i].AddConnection(nodes[iplus]);
nodes[i].AddConnection(nodes[iminus]);
}
//Process intersection nodes - horribly inefficient
bool dirty = true;
int counter = 0;
while (dirty)
{
dirty = false;
for (int i = 0; i < nNodes; ++i)
{
for (int j = 0; j < nodes[i].NConnected; ++j)
{
for (int k = 0; k < nNodes; ++k)
{
if (k == i || nodes[k] == nodes[i].Connected[j])
{
continue;
}
for (int l = 0; l < nodes[k].NConnected; ++l)
{
if (nodes[k].Connected[l] == nodes[i].Connected[j] ||
nodes[k].Connected[l] == nodes[i])
{
continue;
}
//Check intersection
Vector2 intersectPt;
bool crosses = LineTools.LineIntersect(nodes[i].Position, nodes[i].Connected[j].Position,
nodes[k].Position, nodes[k].Connected[l].Position,
out intersectPt);
if (crosses)
{
dirty = true;
//Destroy and re-hook connections at crossing point
PolyNode connj = nodes[i].Connected[j];
PolyNode connl = nodes[k].Connected[l];
nodes[i].Connected[j].RemoveConnection(nodes[i]);
nodes[i].RemoveConnection(connj);
nodes[k].Connected[l].RemoveConnection(nodes[k]);
nodes[k].RemoveConnection(connl);
nodes[nNodes] = new PolyNode(intersectPt);
nodes[nNodes].AddConnection(nodes[i]);
nodes[i].AddConnection(nodes[nNodes]);
nodes[nNodes].AddConnection(nodes[k]);
nodes[k].AddConnection(nodes[nNodes]);
nodes[nNodes].AddConnection(connj);
connj.AddConnection(nodes[nNodes]);
nodes[nNodes].AddConnection(connl);
connl.AddConnection(nodes[nNodes]);
++nNodes;
goto SkipOut;
}
}
}
}
}
SkipOut:
++counter;
}
//Collapse duplicate points
bool foundDupe = true;
int nActive = nNodes;
while (foundDupe)
{
foundDupe = false;
for (int i = 0; i < nNodes; ++i)
{
if (nodes[i].NConnected == 0)
{
continue;
}
for (int j = i + 1; j < nNodes; ++j)
{
if (nodes[j].NConnected == 0)
{
continue;
}
Vector2 diff = nodes[i].Position - nodes[j].Position;
if (diff.LengthSquared <= Settings.Epsilon * Settings.Epsilon)
{
if (nActive <= 3)
{
return(new Vertices());
}
//printf("Found dupe, %d left\n",nActive);
--nActive;
foundDupe = true;
PolyNode inode = nodes[i];
PolyNode jnode = nodes[j];
//Move all of j's connections to i, and orphan j
int njConn = jnode.NConnected;
for (int k = 0; k < njConn; ++k)
{
PolyNode knode = jnode.Connected[k];
Debug.Assert(knode != jnode);
if (knode != inode)
{
inode.AddConnection(knode);
knode.AddConnection(inode);
}
knode.RemoveConnection(jnode);
}
jnode.NConnected = 0;
}
}
}
}
//Now walk the edge of the list
//Find node with minimum y value (max x if equal)
float minY = float.MaxValue;
float maxX = -float.MaxValue;
int minYIndex = -1;
for (int i = 0; i < nNodes; ++i)
{
if (nodes[i].Position.Y < minY && nodes[i].NConnected > 1)
{
minY = nodes[i].Position.Y;
minYIndex = i;
maxX = nodes[i].Position.X;
}
else if (nodes[i].Position.Y == minY && nodes[i].Position.X > maxX && nodes[i].NConnected > 1)
{
minYIndex = i;
maxX = nodes[i].Position.X;
}
}
Vector2 origDir = new Vector2(1.0f, 0.0f);
Vector2[] resultVecs = new Vector2[4 * nNodes];
// nodes may be visited more than once, unfortunately - change to growable array!
int nResultVecs = 0;
PolyNode currentNode = nodes[minYIndex];
PolyNode startNode = currentNode;
Debug.Assert(currentNode.NConnected > 0);
PolyNode nextNode = currentNode.GetRightestConnection(origDir);
if (nextNode == null)
{
Vertices vertices = new Vertices(nResultVecs);
for (int i = 0; i < nResultVecs; ++i)
{
vertices.Add(resultVecs[i]);
}
return(vertices);
}
// Borked, clean up our mess and return
resultVecs[0] = startNode.Position;
++nResultVecs;
while (nextNode != startNode)
{
if (nResultVecs > 4 * nNodes)
{
Debug.Assert(false);
}
resultVecs[nResultVecs++] = nextNode.Position;
PolyNode oldNode = currentNode;
currentNode = nextNode;
nextNode = currentNode.GetRightestConnection(oldNode);
if (nextNode == null)
{
Vertices vertices = new Vertices(nResultVecs);
for (int i = 0; i < nResultVecs; ++i)
{
vertices.Add(resultVecs[i]);
}
return(vertices);
}
// There was a problem, so jump out of the loop and use whatever garbage we've generated so far
}
return(new Vertices());
}