////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Insert the edge at infinity into the edge list for the vertices at infinity. </summary>
/// <remarks> Darrellp, 2/19/2011. </remarks>
/// <param name="edge"> Edge at infinity being added. </param>
/// <param name="leadingVtxCw"> Vertex on the left of infinite poly as we look out. </param>
/// <param name="trailingVtxCw"> Vertex on the right. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
private static void HookEdgeAtInfinityToVerticesAtInfinity(FortuneEdge edge, FortuneVertex leadingVtxCw,
FortuneVertex trailingVtxCw)
{
// if we've only got one edge at infinity
if (leadingVtxCw.FortuneEdges.Count == 1)
{
// Add this one as a placeholder
//
// This will be overwritten later but we have to insert here so that we can insert ourselves at
// index 2. This is just a placeholder.
leadingVtxCw.FortuneEdges.Add(edge);
}
// Add this edge into it's proper position
leadingVtxCw.FortuneEdges.Add(edge);
// If we have three edges
if (trailingVtxCw.FortuneEdges.Count == 3)
{
// Overwrite the placeholder we placed in another call
//
// Here is where the overwriting referred to above occurs
// This will happen on a later call - not on the current one
trailingVtxCw.FortuneEdges[1] = edge;
}
else
{
// Otherwise just add us in to the trailing vertex's list of edges
trailingVtxCw.FortuneEdges.Add(edge);
}
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Produce a vertex at infinity. </summary>
/// <remarks> Darrellp, 2/19/2011. </remarks>
/// <param name="ptDirection"> Direction for the vertex. </param>
/// <param name="fNormalize"> If true we normalize, else not. </param>
/// <returns> The vertex at infinity. </returns>
////////////////////////////////////////////////////////////////////////////////////////////////////
internal static FortuneVertex InfiniteVertex(Vector ptDirection, bool fNormalize = true)
{
var vtx = new FortuneVertex(ptDirection);
vtx.SetInfinite(fNormalize);
return(vtx);
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Add a vertex in the proper place according to _fStartVertexSet. </summary>
/// <remarks> Darrellp, 2/19/2011. </remarks>
/// <param name="vtx"> Vertex to add. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
internal void AddVertex(FortuneVertex vtx)
{
// If we've already set the start vertex
if (_fStartVertexSet)
{
// This is the end vertex
VtxEnd = vtx;
}
else
{
// Make this the start vertex and set the start vertex flag
_fStartVertexSet = true;
VtxStart = vtx;
}
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Splits a doubly infinite edge. </summary>
/// <remarks> Darrellp, 2/18/2011. </remarks>
/// <param name="edge"> Edge we need to split. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
private static void SplitDoublyInfiniteEdge(FortuneEdge edge)
{
// Initialize
var pt1 = edge.Poly1.VoronoiPoint;
var pt2 = edge.Poly2.VoronoiPoint;
var dx = pt2.X - pt1.X;
var dy = pt2.Y - pt1.Y;
var ptMid = new Vector((pt1.X + pt2.X) / 2, (pt1.Y + pt2.Y) / 2);
// Infinite vertices have directions in them rather than locations
var vtx1 = FortuneVertex.InfiniteVertex(new Vector(-dy, dx));
var vtx2 = FortuneVertex.InfiniteVertex(new Vector(dy, -dx));
// Create the new edge an link it in
edge.VtxStart = new FortuneVertex(ptMid);
edge.VtxEnd = vtx1;
var edgeNew = new FortuneEdge {
VtxStart = edge.VtxStart, VtxEnd = vtx2
};
edgeNew.SetPolys(edge.Poly1, edge.Poly2);
edge.Poly1.AddEdge(edgeNew);
edge.Poly2.AddEdge(edgeNew);
((FortuneVertex)edge.VtxStart).Add(edge);
((FortuneVertex)edge.VtxStart).Add(edgeNew);
vtx1.Add(edge);
vtx2.Add(edgeNew);
edge.FSplit = edgeNew.FSplit = true;
// If the edge "leans right"
//
// We have to be very picky about how we set up the left and right
// polygons for our new rays.
// ReSharper disable once CompareOfFloatsByEqualityOperator
if (dx == 0 || dx * dy > 0) // dy == 0 case needs to fall through...
{
// Set up left and right polygons one way
edge.PolyRight = edgeNew.PolyLeft = edge.Poly1;
edge.PolyLeft = edgeNew.PolyRight = edge.Poly2;
}
else
{
// Set left and right polygons the other way
edge.PolyLeft = edgeNew.PolyRight = edge.Poly1;
edge.PolyRight = edgeNew.PolyLeft = edge.Poly2;
}
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Turn a null endpoint of the ray into an infinite vertex. </summary>
/// <remarks> Darrellp, 2/18/2011. </remarks>
/// <param name="edge"> Edge with the null vertex. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
private static void ProcessRay(FortuneEdge edge)
{
// If it's the start vertex that's null
if (edge.VtxStart == null)
{
// Swap the vertices
//
// This is what justifies the assertion in WeEdge.FLeftOf() (see the code).
edge.VtxStart = edge.VtxEnd;
edge.VtxEnd = null;
}
// Replace the null vertex with an infinite vertex
var pt1 = edge.Poly1.VoronoiPoint;
var pt2 = edge.Poly2.VoronoiPoint;
var ptMid = new Vector((pt1.X + pt2.X) / 2, (pt1.Y + pt2.Y) / 2);
// Point the ray in the proper direction
//
// We have to be careful to get this ray pointed in the proper orientation. At
// this point we just have a vertex and points which are the original voronoi
// points which created these infinite polys. That's enough to figure out the
// absolute direction the voronoi points but not enough to determine which "orientation"
// it points along. To do this, we find the third polygon at the "base" of this ray
// and point the ray "away" from it.
var polyThird = ((FortuneVertex)edge.VtxStart).PolyThird(edge);
var fThirdOnLeft = FLeft(pt1, pt2, polyThird.VoronoiPoint);
var dx = pt2.X - pt1.X;
var dy = pt2.Y - pt1.Y;
var ptProposedDirection = new Vector(dy, -dx);
var ptInProposedDirection = new Vector(ptMid.X + dy, ptMid.Y - dx);
var fProposedOnLeft = FLeft(pt1, pt2, ptInProposedDirection);
// Do we need to reverse orientation?
if (fProposedOnLeft == fThirdOnLeft)
{
// Do it
ptProposedDirection.X = -ptProposedDirection.X;
ptProposedDirection.Y = -ptProposedDirection.Y;
}
// Create the new infinite vertex and add it to our edge
edge.VtxEnd = FortuneVertex.InfiniteVertex(ptProposedDirection);
((FortuneVertex)edge.VtxEnd).FortuneEdges.Add(edge);
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary>
/// Get the next edge in both the cw and ccw directions from this edge at the given 3 valent
/// vertex.
/// </summary>
/// <remarks>
/// This is the simplest and most common case. It's called before the winged edge stuff is set up
/// so we have to search manually. The edges have been sorted in clockwise order however.
/// Darrellp, 2/19/2011.
/// </remarks>
/// <param name="vtx"> vertex to use. </param>
/// <param name="edgeCW"> [out] returned cw edge. </param>
/// <param name="edgeCCW"> [out] returned ccw edge. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
private void GetSuccessorEdgesFrom3ValentVertex(
FortuneVertex vtx,
out FortuneEdge edgeCW,
out FortuneEdge edgeCCW)
{
// Locals
int iEdge;
// Figure out which of the edges is ours
for (iEdge = 0; iEdge < 3; iEdge++)
{
// If the current edge is us
if (ReferenceEquals(vtx.FortuneEdges[iEdge], this))
{
break;
}
}
// The next two edges, in order, are the onew we're looking for
edgeCW = vtx.FortuneEdges[(iEdge + 1) % 3];
edgeCCW = vtx.FortuneEdges[(iEdge + 2) % 3];
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary>
/// Get the next edge in both the cw and ccw directions from this edge at the given vertex.
/// </summary>
/// <remarks>
/// This routine is called before they've been set up as winged edges so we have to search them
/// out ourselves. The edges have been ordered in CW order, however.
/// Darrellp, 2/19/2011.
/// </remarks>
/// <param name="vtx"> vertex to use. </param>
/// <param name="edgeCW"> [out] returned cw edge. </param>
/// <param name="edgeCCW"> [out] returned ccw edge. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
private void GetSuccessorEdgesFromVertex(
FortuneVertex vtx,
out FortuneEdge edgeCW,
out FortuneEdge edgeCCW)
{
// Are we free of zero length edges?
if (vtx.FortuneEdges.Count == 3)
{
// Do the extremely simple, extremely common 3 valent case
GetSuccessorEdgesFrom3ValentVertex(vtx, out edgeCW, out edgeCCW);
}
else
{
// Locals
int iEdge;
int cEdges;
// If we're looking at our start vertex
if (vtx == VtxStart)
{
// Find our place in the list of edges for start vertex
iEdge = EdgeIndex(true);
cEdges = ((FortuneVertex)VtxStart).CtEdges;
}
else
{
// Find our place in the list of edges for end vertex
iEdge = EdgeIndex(false);
cEdges = ((FortuneVertex)VtxEnd).CtEdges;
}
// Get our immediate neighbors on the edge list
edgeCW = vtx.FortuneEdges[(iEdge + 1) % cEdges];
edgeCCW = vtx.FortuneEdges[(iEdge + cEdges - 1) % cEdges];
}
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary>
/// Remove a parabola node from the beachline since it's being squeezed out and insert a vertex
/// into the voronoi diagram.
/// </summary>
/// <remarks>
/// This happens when a circle event occurs. It's a rather delicate operation. From the point of
/// view of the voronoi diagram, we have two edges from above coming together into the newly
/// created vertex and a new edge created which descends below it. This is really where the meat
/// of actually creating the voronoi diagram occurs. One of the important details which seems to
/// be left totally out of the book is the importance of keeping accurate left and right sibling
/// pointers on the leaf nodes. Since each leaf node represents a parabola in the beachline,
/// these pointers represent the set of parabolas from the left to the right of the beachline.
/// In a case like this where a parabola is being squeezed out, it's left and right siblings will
/// not butt up against each other forming a new edge and we need to be able to locate both these
/// nodes in order to make everything come out right.
/// This is very persnickety code.
/// </remarks>
/// <param name="cevt"> Circle event which caused this. </param>
/// <param name="lfnEliminated"> Leaf node for the parabola being eliminated. </param>
/// <param name="voronoiVertex"> The new vertex to be inserted into the voronoi diagram. </param>
/// <param name="evq"> Event queue. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
internal void RemoveNodeAndInsertVertex(CircleEvent cevt, LeafNode lfnEliminated, Vector voronoiVertex,
EventQueue evq)
{
// Initialize
var yScanLine = cevt.Pt.Y;
// Determine whether we're the left or right child of our parent
var fLeftChildEliminated = lfnEliminated.IsLeftChild;
var innParent = lfnEliminated.NdParent;
// Retrieve sibling nodes
var lfnLeft = lfnEliminated.LeftAdjacentLeaf;
var lfnRight = lfnEliminated.RightAdjacentLeaf;
var lfnNearSibling = fLeftChildEliminated ? lfnRight : lfnLeft;
// Remove from the queue any circle events which involve the eliminated node or its siblings
RemoveAssociatedCircleEvents(lfnEliminated, evq);
// remove the leaf from the tree and rearrange the nodes around it
RemoveLeaf(lfnEliminated);
// Locate the internal node which represents the breakpoint between our near and far sibling
var innFarSiblingEdge = lfnNearSibling.InnFindSiblingEdge(fLeftChildEliminated);
// Get the edges being developed on each side of us
//
// The meeting of these edges is what causes the creation of our vertex in the voronoi diagram
var edgeNearSibling = innParent.Edge;
var edgeFarSibling = innFarSiblingEdge.Edge;
// Create a new fortune vertex to insert into the diagram
var vertex = new FortuneVertex {
Pt = voronoiVertex
};
// Give both edges from above their brand new vertex - hooray!
edgeFarSibling.AddVertex(vertex);
edgeNearSibling.AddVertex(vertex);
// Is this a zero length edge?
//
// Some of our incoming edges are zero length due to cocircular points,
// so keep track of it in the polys which border them. This will be used
// later in Fortune.BuildWingedEdge() to determine when to try and remove
// zero length edges.
if (cevt.FZeroLength)
{
// Mark the poly as having a zero length edge.
//
// We can't eliminate it here because most of our winged edge machinery
// needs to assume three edges entering every vertex. We'll take care of
// it later in post-processing. This flag is the signal to do that.
SetZeroLengthFlagOnPolys(edgeNearSibling, edgeFarSibling);
}
// RQS- Add edges to the vertex in proper clockwise direction
if (fLeftChildEliminated)
{
vertex.Add(edgeFarSibling);
vertex.Add(edgeNearSibling);
}
else
{
vertex.Add(edgeNearSibling);
vertex.Add(edgeFarSibling);
}
// -RQS
// Create the new edge which emerges below this vertex
var edge = new FortuneEdge();
edge.AddVertex(vertex);
vertex.Add(edge);
// Add the edge to our siblings
//
// Since lfnEliminated is being removed, it's siblings now butt against each other forming
// the new edge so save that edge on the internal node and add it to the poly for the
// generator represented by the near sibling. This means that polygon edges get added in
// a fairly random order. They'll be sorted in postprocessing.
// Add it to our winged edge polygon
lfnNearSibling.Poly.AddEdge(edge);
// Also add it to our beachline sibling
innFarSiblingEdge.Edge = edge;
// Fix up the siblings and the edges/polygons they border
//
// The inner node which used to represent one of the incoming edges now takes on responsibility
// for the newly created edge so it no longer borders the polygon represented by the eliminated
// leaf node, but rather borders the polygon represented by its sibling on the other side.
// Also, that polygon receives a new edge.
// If we eliminated the left child from a parent
if (fLeftChildEliminated)
{
// Reset the data on the inner node representing our far sibling
innFarSiblingEdge.PolyRight = lfnNearSibling.Poly;
innFarSiblingEdge.PolyLeft.AddEdge(edge);
// If this event represented a zero length edge
if (cevt.FZeroLength)
{
// Keep track of it in the fortune polygon
innFarSiblingEdge.PolyLeft.FZeroLengthEdge = true;
}
}
else
{
// Reset the data on the inner node representing our far sibling
innFarSiblingEdge.PolyLeft = lfnNearSibling.Poly;
innFarSiblingEdge.PolyRight.AddEdge(edge);
// If this event represented a zero length edge
if (cevt.FZeroLength)
{
// Keep track of it in the fortune polygon
innFarSiblingEdge.PolyRight.FZeroLengthEdge = true;
}
}
// Set the polygons which border the new edge
edge.SetPolys(innFarSiblingEdge.PolyRight, innFarSiblingEdge.PolyLeft);
// Create new circle events for our siblings
//
// Now that we're squeezed out, our former left and right siblings become immediate siblings
// so we need to set new circle events to represent when they get squeezed out by their
// newly acquired siblings
CreateCircleEventFromTriple(lfnLeft.LeftAdjacentLeaf, lfnLeft, lfnRight, yScanLine, evq);
CreateCircleEventFromTriple(lfnLeft, lfnRight, lfnRight.RightAdjacentLeaf, yScanLine, evq);
}
