////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Adds a circle event. </summary>
/// <remarks> Darrellp, 2/21/2011. </remarks>
/// <param name="cevt"> The event to add. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
internal void AddCircleEvent(CircleEvent cevt)
{
// Add to the priority queue
Add(cevt);
// We also have to add them to our linked list of circle events
CircleEvents.AddFirst(cevt);
// Keeping track of their LinkedListNode allows us to delete them efficiently later
cevt.LinkedListNode = CircleEvents.First;
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Remove the circle event which snuffs this node's parabola from the event queue. </summary>
/// <remarks> Darrellp, 2/18/2011. </remarks>
/// <param name="evq"> Event queue. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
internal void DeleteAssociatedCircleEvent(EventQueue evq)
{
// If we've got a circle event
if (_cevt != null)
{
// Delete it
evq.Delete(_cevt);
if (_cevt.LinkedListNode != null)
{
evq.CircleEvents.Remove(_cevt.LinkedListNode);
}
_cevt = null;
}
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Creates a circle event. </summary>
/// <remarks>Circle events are created at the circumcenters of three sites - the sites for poly1/2/3.</remarks>
/// <param name="poly1"> The first polygon. </param>
/// <param name="poly2"> The second polygon. </param>
/// <param name="poly3"> The third polygon. </param>
/// <param name="yScanLine"> The y coordinate scan line. </param>
/// <returns> A new circle event. </returns>
////////////////////////////////////////////////////////////////////////////////////////////////////
internal static CircleEvent CreateCircleEvent(FortunePoly poly1, FortunePoly poly2, FortunePoly poly3,
double yScanLine)
{
// Locals
CircleEvent cevtRet = null;
// Determine a circumcenter for the sites of poly1/2/3.
if (Geometry2D.FFindCircumcenter(poly1.VoronoiPoint, poly2.VoronoiPoint, poly3.VoronoiPoint, out var ptCenter))
{
// Determine y coordinate for the side of the circle
// The event will fire when the scan line hits that y position
var radius = Geometry2D.Distance(poly1.VoronoiPoint, ptCenter);
ptCenter.Y -= radius;
// If the circumcenter is above the scan line we've already passed it by, so don't put it in the queue
if (ptCenter.Y <= yScanLine)
{
cevtRet = new CircleEvent(ptCenter, radius);
}
}
return(cevtRet);
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <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);
}
/// <summary>
/// Remove events from the queue and handle them one at a time.
/// </summary>
private void ProcessEvents()
{
// Create an impossible fictional "previous event"
FortuneEvent evtPrev = new CircleEvent(new Vector(Single.MaxValue, Single.MaxValue), 0);
// While there are events in the queue
while (QevEvents.Count > 0)
{
// Get the next event
//
// Events are pulled off in top to bottom, left to right, site event before
// circle event order. This ensures that events/sites at identical locations
// will be pulled off one after the other which allows us to cull them.
var evt = QevEvents.Pop();
// If we've got a pair of identically placed events
if (FCloseEnough(evt.Pt, evtPrev.Pt))
{
// Locals
var tpPrev = evtPrev.GetType();
var tpCur = evt.GetType();
// If the previous event was a site event
if (tpPrev == typeof(SiteEvent))
{
// And the current one is also
if (tpCur == typeof(SiteEvent))
{
// Skip identical site events.
//
// This handles cases where the same point is in the input data two or more times.
continue;
}
}
// Else if it's a circle event
else if (tpCur == typeof(CircleEvent))
{
// Locals
var cevt = evt as CircleEvent;
var cevtPrev = evtPrev as CircleEvent;
// If we have identically placed circle events
//
// Identically placed circle events still have to be processed but we handle the
// case specially. The implication of identically placed circle events is that
// we had four or more cocircular points which implies that the polygons
// for those points come together to a point. Since we only allow for vertices
// of order three during voronoi processing, we create "zero length" edges for the
// polygons which meet at that common point. These will be removed later in postprocessing.
//
// ReSharper disable PossibleNullReferenceException
if (FCloseEnough(cevt.VoronoiVertex, cevtPrev.VoronoiVertex))
{
// We're going to create a zero length edge.
cevt.FZeroLength = true;
}
// ReSharper restore PossibleNullReferenceException
}
}
// Handle the event
evt.Handle(this);
evtPrev = evt;
}
}
////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary> Set the circle event which snuff's this node's parabola. </summary>
/// <remarks> Darrellp, 2/18/2011. </remarks>
/// <param name="cevt"> The cevt. </param>
////////////////////////////////////////////////////////////////////////////////////////////////////
internal void SetCircleEvent(CircleEvent cevt)
{
_cevt = cevt;
}
