public DCEL ComputeVoronoiDiagram(IEnumerable<Site> sites)
{
var state = new State
{
BeachLine = null,
EventQueue = CreateEventQueueWithSiteEvents(sites),
SweepLineY = double.MaxValue,
Faces = new Dictionary<Site, Face>(),
HalfEdges = new List<HalfEdge>(),
Vertexes = new List<Vertex>()
};
DrainEvents(state);
throw new System.NotImplementedException();
}
/// <summary>
/// Processes all events from the event queue, including any
/// discovered circle events.
/// </summary>
private void DrainEvents(State state)
{
while(state.EventQueue.Count > 0)
{
var currentEvent = state.EventQueue.Dequeue();
// The sweep line should always decrease monotonically.
if (currentEvent.YCoordinate > state.SweepLineY)
throw new SanityCheckFailedException(string.Format(
"Retrieved a {0} from the event queue whose y-coordinate ({1}) was greater than the sweep line's y-coordinate ({2}). The sweep line's y coordinate should monotonically decrease as the algorithm progresses.",
currentEvent.GetType().Name,
currentEvent.YCoordinate,
state.SweepLineY));
// Advance the sweep line to the y-coordinate of the current event.
state.SweepLineY = currentEvent.YCoordinate;
// Handle the event based on its type.
if (currentEvent is SiteEvent)
HandleSiteEvent((SiteEvent)currentEvent, state);
else
HandleCircleEvent((CircleEvent)currentEvent, state);
}
}
private void HandleSiteEvent(SiteEvent ev, State state)
{
// If the beach line data structure is empty, initialize
// it with the arc created by the new site into it and return.
if (state.BeachLine == null)
{
state.BeachLine = new ArcNode(ev.Site);
return;
}
// Find the arc split by the new site.
var splitArcNode = Helpers.FindArcSplitByNewSite(ev.Site.Position, state.BeachLine);
// If the arc being split has a circle event, it is a false alarm,
// so delete it from the event queue.
if (splitArcNode.DisappearanceEvent != null)
state.EventQueue.Remove(splitArcNode.DisappearanceEvent.Index);
// The following pieces of the final Voronoi diagram are created
// during a site event:
// - The Face defined by the new site.
// - Both HalfEdges of the edge that will be traced out by the
// two new breakpoints.
var newFace = new Face {UserData = ev.Site.UserData};
var halfEdgeFacingOldSite = new HalfEdge();
var halfEdgeFacingNewSite = new HalfEdge();
state.Faces.Add(ev.Site, newFace);
state.HalfEdges.Add(halfEdgeFacingOldSite);
state.HalfEdges.Add(halfEdgeFacingNewSite);
// Link all the diagram pieces together that can be linked at this time.
halfEdgeFacingOldSite.Interior = state.Faces[splitArcNode.DefiningSite];
halfEdgeFacingNewSite.Interior = newFace;
halfEdgeFacingOldSite.Twin = halfEdgeFacingNewSite;
halfEdgeFacingNewSite.Twin = halfEdgeFacingOldSite;
// During a site event, an existing arc is split into two
// new arcs with an additional arc in the middle. We reflect
// this change in beach line status tree data structure by
// replacing the split arc node with a new subtree with five
// nodes total: two for the two new breakpoints, and three
// for the three new arcs on the beach line.
var leftBP = new BreakpointNode(ev.Site, splitArcNode.DefiningSite, halfEdgeFacingOldSite, true);
var rightBP = new BreakpointNode(ev.Site, splitArcNode.DefiningSite, halfEdgeFacingNewSite, false);
var leftArc = new ArcNode(splitArcNode.DefiningSite);
var middleArc = new ArcNode(ev.Site);
var rightArc = new ArcNode(splitArcNode.DefiningSite);
// Set up new subtree.
leftBP.LeftChild = leftArc;
leftBP.RightChild = rightBP;
rightBP.LeftChild = middleArc;
rightBP.RightChild = rightArc;
rightBP.Parent = leftBP;
leftArc.Parent = leftBP;
middleArc.Parent = rightBP;
rightArc.Parent = rightBP;
// Graft new subtree into existing beach line status tree data structure.
// First check for the special case where the split arc node was the
// root element of the tree (aka the only element).
if (splitArcNode.Parent == null)
{
if (state.BeachLine != splitArcNode)
throw new SanityCheckFailedException(
"The splitArcNode's parent was null, but it was not the root of the beach line status tree data structure.");
state.BeachLine = leftBP;
}
// Otherwise, graft into existing tree. Here is where
// we would perform rebalancing operations on the tree.
else
{
if (splitArcNode.Parent.LeftChild == splitArcNode)
{
splitArcNode.Parent.LeftChild = leftBP;
leftBP.Parent = splitArcNode.Parent;
}
else
{
splitArcNode.Parent.RightChild = leftBP;
leftBP.Parent = splitArcNode.Parent;
}
}
}
private void HandleCircleEvent(CircleEvent ev, State state)
{
}
