begin refactor to use quadtree

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diff --git a/modules/3rdparty/rhill-voronoi-core.js b/modules/3rdparty/rhill-voronoi-core.js
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+/*!
+Copyright (C) 2010-2013 Raymond Hill: https://github.com/gorhill/Javascript-Voronoi
+MIT License: See https://github.com/gorhill/Javascript-Voronoi/LICENSE.md
+*/
+/*
+Author: Raymond Hill (rhill@raymondhill.net)
+Contributor: Jesse Morgan (morgajel@gmail.com)
+File: rhill-voronoi-core.js
+Version: 0.98
+Date: January 21, 2013
+Description: This is my personal Javascript implementation of
+Steven Fortune's algorithm to compute Voronoi diagrams.
+
+License: See https://github.com/gorhill/Javascript-Voronoi/LICENSE.md
+Credits: See https://github.com/gorhill/Javascript-Voronoi/CREDITS.md
+History: See https://github.com/gorhill/Javascript-Voronoi/CHANGELOG.md
+
+## Usage:
+
+  var sites = [{x:300,y:300}, {x:100,y:100}, {x:200,y:500}, {x:250,y:450}, {x:600,y:150}];
+  // xl, xr means x left, x right
+  // yt, yb means y top, y bottom
+  var bbox = {xl:0, xr:800, yt:0, yb:600};
+  var voronoi = new Voronoi();
+  // pass an object which exhibits xl, xr, yt, yb properties. The bounding
+  // box will be used to connect unbound edges, and to close open cells
+  result = voronoi.compute(sites, bbox);
+  // render, further analyze, etc.
+
+Return value:
+  An object with the following properties:
+
+  result.vertices = an array of unordered, unique Voronoi.Vertex objects making
+    up the Voronoi diagram.
+  result.edges = an array of unordered, unique Voronoi.Edge objects making up
+    the Voronoi diagram.
+  result.cells = an array of Voronoi.Cell object making up the Voronoi diagram.
+    A Cell object might have an empty array of halfedges, meaning no Voronoi
+    cell could be computed for a particular cell.
+  result.execTime = the time it took to compute the Voronoi diagram, in
+    milliseconds.
+
+Voronoi.Vertex object:
+  x: The x position of the vertex.
+  y: The y position of the vertex.
+
+Voronoi.Edge object:
+  lSite: the Voronoi site object at the left of this Voronoi.Edge object.
+  rSite: the Voronoi site object at the right of this Voronoi.Edge object (can
+    be null).
+  va: an object with an 'x' and a 'y' property defining the start point
+    (relative to the Voronoi site on the left) of this Voronoi.Edge object.
+  vb: an object with an 'x' and a 'y' property defining the end point
+    (relative to Voronoi site on the left) of this Voronoi.Edge object.
+
+  For edges which are used to close open cells (using the supplied bounding
+  box), the rSite property will be null.
+
+Voronoi.Cell object:
+  site: the Voronoi site object associated with the Voronoi cell.
+  halfedges: an array of Voronoi.Halfedge objects, ordered counterclockwise,
+    defining the polygon for this Voronoi cell.
+
+Voronoi.Halfedge object:
+  site: the Voronoi site object owning this Voronoi.Halfedge object.
+  edge: a reference to the unique Voronoi.Edge object underlying this
+    Voronoi.Halfedge object.
+  getStartpoint(): a method returning an object with an 'x' and a 'y' property
+    for the start point of this halfedge. Keep in mind halfedges are always
+    countercockwise.
+  getEndpoint(): a method returning an object with an 'x' and a 'y' property
+    for the end point of this halfedge. Keep in mind halfedges are always
+    countercockwise.
+
+TODO: Identify opportunities for performance improvement.
+
+TODO: Let the user close the Voronoi cells, do not do it automatically. Not only let
+      him close the cells, but also allow him to close more than once using a different
+      bounding box for the same Voronoi diagram.
+*/
+
+/*global Math */
+
+// ---------------------------------------------------------------------------
+
+function Voronoi() {
+    this.vertices = null;
+    this.edges = null;
+    this.cells = null;
+    this.toRecycle = null;
+    this.beachsectionJunkyard = [];
+    this.circleEventJunkyard = [];
+    this.vertexJunkyard = [];
+    this.edgeJunkyard = [];
+    this.cellJunkyard = [];
+    }
+
+// ---------------------------------------------------------------------------
+
+Voronoi.prototype.reset = function() {
+    if (!this.beachline) {
+        this.beachline = new this.RBTree();
+        }
+    // Move leftover beachsections to the beachsection junkyard.
+    if (this.beachline.root) {
+        var beachsection = this.beachline.getFirst(this.beachline.root);
+        while (beachsection) {
+            this.beachsectionJunkyard.push(beachsection); // mark for reuse
+            beachsection = beachsection.rbNext;
+            }
+        }
+    this.beachline.root = null;
+    if (!this.circleEvents) {
+        this.circleEvents = new this.RBTree();
+        }
+    this.circleEvents.root = this.firstCircleEvent = null;
+    this.vertices = [];
+    this.edges = [];
+    this.cells = [];
+    };
+
+Voronoi.prototype.sqrt = Math.sqrt;
+Voronoi.prototype.abs = Math.abs;
+Voronoi.prototype.ε = Voronoi.ε = 1e-9;
+Voronoi.prototype.invε = Voronoi.invε = 1.0 / Voronoi.ε;
+Voronoi.prototype.equalWithEpsilon = function(a,b){return this.abs(a-b)<1e-9;};
+Voronoi.prototype.greaterThanWithEpsilon = function(a,b){return a-b>1e-9;};
+Voronoi.prototype.greaterThanOrEqualWithEpsilon = function(a,b){return b-a<1e-9;};
+Voronoi.prototype.lessThanWithEpsilon = function(a,b){return b-a>1e-9;};
+Voronoi.prototype.lessThanOrEqualWithEpsilon = function(a,b){return a-b<1e-9;};
+
+// ---------------------------------------------------------------------------
+// Red-Black tree code (based on C version of "rbtree" by Franck Bui-Huu
+// https://github.com/fbuihuu/libtree/blob/master/rb.c
+
+Voronoi.prototype.RBTree = function() {
+    this.root = null;
+    };
+
+Voronoi.prototype.RBTree.prototype.rbInsertSuccessor = function(node, successor) {
+    var parent;
+    if (node) {
+        // >>> rhill 2011-05-27: Performance: cache previous/next nodes
+        successor.rbPrevious = node;
+        successor.rbNext = node.rbNext;
+        if (node.rbNext) {
+            node.rbNext.rbPrevious = successor;
+            }
+        node.rbNext = successor;
+        // <<<
+        if (node.rbRight) {
+            // in-place expansion of node.rbRight.getFirst();
+            node = node.rbRight;
+            while (node.rbLeft) {node = node.rbLeft;}
+            node.rbLeft = successor;
+            }
+        else {
+            node.rbRight = successor;
+            }
+        parent = node;
+        }
+    // rhill 2011-06-07: if node is null, successor must be inserted
+    // to the left-most part of the tree
+    else if (this.root) {
+        node = this.getFirst(this.root);
+        // >>> Performance: cache previous/next nodes
+        successor.rbPrevious = null;
+        successor.rbNext = node;
+        node.rbPrevious = successor;
+        // <<<
+        node.rbLeft = successor;
+        parent = node;
+        }
+    else {
+        // >>> Performance: cache previous/next nodes
+        successor.rbPrevious = successor.rbNext = null;
+        // <<<
+        this.root = successor;
+        parent = null;
+        }
+    successor.rbLeft = successor.rbRight = null;
+    successor.rbParent = parent;
+    successor.rbRed = true;
+    // Fixup the modified tree by recoloring nodes and performing
+    // rotations (2 at most) hence the red-black tree properties are
+    // preserved.
+    var grandpa, uncle;
+    node = successor;
+    while (parent && parent.rbRed) {
+        grandpa = parent.rbParent;
+        if (parent === grandpa.rbLeft) {
+            uncle = grandpa.rbRight;
+            if (uncle && uncle.rbRed) {
+                parent.rbRed = uncle.rbRed = false;
+                grandpa.rbRed = true;
+                node = grandpa;
+                }
+            else {
+                if (node === parent.rbRight) {
+                    this.rbRotateLeft(parent);
+                    node = parent;
+                    parent = node.rbParent;
+                    }
+                parent.rbRed = false;
+                grandpa.rbRed = true;
+                this.rbRotateRight(grandpa);
+                }
+            }
+        else {
+            uncle = grandpa.rbLeft;
+            if (uncle && uncle.rbRed) {
+                parent.rbRed = uncle.rbRed = false;
+                grandpa.rbRed = true;
+                node = grandpa;
+                }
+            else {
+                if (node === parent.rbLeft) {
+                    this.rbRotateRight(parent);
+                    node = parent;
+                    parent = node.rbParent;
+                    }
+                parent.rbRed = false;
+                grandpa.rbRed = true;
+                this.rbRotateLeft(grandpa);
+                }
+            }
+        parent = node.rbParent;
+        }
+    this.root.rbRed = false;
+    };
+
+Voronoi.prototype.RBTree.prototype.rbRemoveNode = function(node) {
+    // >>> rhill 2011-05-27: Performance: cache previous/next nodes
+    if (node.rbNext) {
+        node.rbNext.rbPrevious = node.rbPrevious;
+        }
+    if (node.rbPrevious) {
+        node.rbPrevious.rbNext = node.rbNext;
+        }
+    node.rbNext = node.rbPrevious = null;
+    // <<<
+    var parent = node.rbParent,
+        left = node.rbLeft,
+        right = node.rbRight,
+        next;
+    if (!left) {
+        next = right;
+        }
+    else if (!right) {
+        next = left;
+        }
+    else {
+        next = this.getFirst(right);
+        }
+    if (parent) {
+        if (parent.rbLeft === node) {
+            parent.rbLeft = next;
+            }
+        else {
+            parent.rbRight = next;
+            }
+        }
+    else {
+        this.root = next;
+        }
+    // enforce red-black rules
+    var isRed;
+    if (left && right) {
+        isRed = next.rbRed;
+        next.rbRed = node.rbRed;
+        next.rbLeft = left;
+        left.rbParent = next;
+        if (next !== right) {
+            parent = next.rbParent;
+            next.rbParent = node.rbParent;
+            node = next.rbRight;
+            parent.rbLeft = node;
+            next.rbRight = right;
+            right.rbParent = next;
+            }
+        else {
+            next.rbParent = parent;
+            parent = next;
+            node = next.rbRight;
+            }
+        }
+    else {
+        isRed = node.rbRed;
+        node = next;
+        }
+    // 'node' is now the sole successor's child and 'parent' its
+    // new parent (since the successor can have been moved)
+    if (node) {
+        node.rbParent = parent;
+        }
+    // the 'easy' cases
+    if (isRed) {return;}
+    if (node && node.rbRed) {
+        node.rbRed = false;
+        return;
+        }
+    // the other cases
+    var sibling;
+    do {
+        if (node === this.root) {
+            break;
+            }
+        if (node === parent.rbLeft) {
+            sibling = parent.rbRight;
+            if (sibling.rbRed) {
+                sibling.rbRed = false;
+                parent.rbRed = true;
+                this.rbRotateLeft(parent);
+                sibling = parent.rbRight;
+                }
+            if ((sibling.rbLeft && sibling.rbLeft.rbRed) || (sibling.rbRight && sibling.rbRight.rbRed)) {
+                if (!sibling.rbRight || !sibling.rbRight.rbRed) {
+                    sibling.rbLeft.rbRed = false;
+                    sibling.rbRed = true;
+                    this.rbRotateRight(sibling);
+                    sibling = parent.rbRight;
+                    }
+                sibling.rbRed = parent.rbRed;
+                parent.rbRed = sibling.rbRight.rbRed = false;
+                this.rbRotateLeft(parent);
+                node = this.root;
+                break;
+                }
+            }
+        else {
+            sibling = parent.rbLeft;
+            if (sibling.rbRed) {
+                sibling.rbRed = false;
+                parent.rbRed = true;
+                this.rbRotateRight(parent);
+                sibling = parent.rbLeft;
+                }
+            if ((sibling.rbLeft && sibling.rbLeft.rbRed) || (sibling.rbRight && sibling.rbRight.rbRed)) {
+                if (!sibling.rbLeft || !sibling.rbLeft.rbRed) {
+                    sibling.rbRight.rbRed = false;
+                    sibling.rbRed = true;
+                    this.rbRotateLeft(sibling);
+                    sibling = parent.rbLeft;
+                    }
+                sibling.rbRed = parent.rbRed;
+                parent.rbRed = sibling.rbLeft.rbRed = false;
+                this.rbRotateRight(parent);
+                node = this.root;
+                break;
+                }
+            }
+        sibling.rbRed = true;
+        node = parent;
+        parent = parent.rbParent;
+    } while (!node.rbRed);
+    if (node) {node.rbRed = false;}
+    };
+
+Voronoi.prototype.RBTree.prototype.rbRotateLeft = function(node) {
+    var p = node,
+        q = node.rbRight, // can't be null
+        parent = p.rbParent;
+    if (parent) {
+        if (parent.rbLeft === p) {
+            parent.rbLeft = q;
+            }
+        else {
+            parent.rbRight = q;
+            }
+        }
+    else {
+        this.root = q;
+        }
+    q.rbParent = parent;
+    p.rbParent = q;
+    p.rbRight = q.rbLeft;
+    if (p.rbRight) {
+        p.rbRight.rbParent = p;
+        }
+    q.rbLeft = p;
+    };
+
+Voronoi.prototype.RBTree.prototype.rbRotateRight = function(node) {
+    var p = node,
+        q = node.rbLeft, // can't be null
+        parent = p.rbParent;
+    if (parent) {
+        if (parent.rbLeft === p) {
+            parent.rbLeft = q;
+            }
+        else {
+            parent.rbRight = q;
+            }
+        }
+    else {
+        this.root = q;
+        }
+    q.rbParent = parent;
+    p.rbParent = q;
+    p.rbLeft = q.rbRight;
+    if (p.rbLeft) {
+        p.rbLeft.rbParent = p;
+        }
+    q.rbRight = p;
+    };
+
+Voronoi.prototype.RBTree.prototype.getFirst = function(node) {
+    while (node.rbLeft) {
+        node = node.rbLeft;
+        }
+    return node;
+    };
+
+Voronoi.prototype.RBTree.prototype.getLast = function(node) {
+    while (node.rbRight) {
+        node = node.rbRight;
+        }
+    return node;
+    };
+
+// ---------------------------------------------------------------------------
+// Diagram methods
+
+Voronoi.prototype.Diagram = function(site) {
+    this.site = site;
+    };
+
+// ---------------------------------------------------------------------------
+// Cell methods
+
+Voronoi.prototype.Cell = function(site) {
+    this.site = site;
+    this.halfedges = [];
+    this.closeMe = false;
+    };
+
+Voronoi.prototype.Cell.prototype.init = function(site) {
+    this.site = site;
+    this.halfedges = [];
+    this.closeMe = false;
+    return this;
+    };
+
+Voronoi.prototype.createCell = function(site) {
+    var cell = this.cellJunkyard.pop();
+    if ( cell ) {
+        return cell.init(site);
+        }
+    return new this.Cell(site);
+    };
+
+Voronoi.prototype.Cell.prototype.prepareHalfedges = function() {
+    var halfedges = this.halfedges,
+        iHalfedge = halfedges.length,
+        edge;
+    // get rid of unused halfedges
+    // rhill 2011-05-27: Keep it simple, no point here in trying
+    // to be fancy: dangling edges are a typically a minority.
+    while (iHalfedge--) {
+        edge = halfedges[iHalfedge].edge;
+        if (!edge.vb || !edge.va) {
+            halfedges.splice(iHalfedge,1);
+            }
+        }
+
+    // rhill 2011-05-26: I tried to use a binary search at insertion
+    // time to keep the array sorted on-the-fly (in Cell.addHalfedge()).
+    // There was no real benefits in doing so, performance on
+    // Firefox 3.6 was improved marginally, while performance on
+    // Opera 11 was penalized marginally.
+    halfedges.sort(function(a,b){return b.angle-a.angle;});
+    return halfedges.length;
+    };
+
+// Return a list of the neighbor Ids
+Voronoi.prototype.Cell.prototype.getNeighborIds = function() {
+    var neighbors = [],
+        iHalfedge = this.halfedges.length,
+        edge;
+    while (iHalfedge--){
+        edge = this.halfedges[iHalfedge].edge;
+        if (edge.lSite !== null && edge.lSite.voronoiId != this.site.voronoiId) {
+            neighbors.push(edge.lSite.voronoiId);
+            }
+        else if (edge.rSite !== null && edge.rSite.voronoiId != this.site.voronoiId){
+            neighbors.push(edge.rSite.voronoiId);
+            }
+        }
+    return neighbors;
+    };
+
+// Compute bounding box
+//
+Voronoi.prototype.Cell.prototype.getBbox = function() {
+    var halfedges = this.halfedges,
+        iHalfedge = halfedges.length,
+        xmin = Infinity,
+        ymin = Infinity,
+        xmax = -Infinity,
+        ymax = -Infinity,
+        v, vx, vy;
+    while (iHalfedge--) {
+        v = halfedges[iHalfedge].getStartpoint();
+        vx = v.x;
+        vy = v.y;
+        if (vx < xmin) {xmin = vx;}
+        if (vy < ymin) {ymin = vy;}
+        if (vx > xmax) {xmax = vx;}
+        if (vy > ymax) {ymax = vy;}
+        // we dont need to take into account end point,
+        // since each end point matches a start point
+        }
+    return {
+        x: xmin,
+        y: ymin,
+        width: xmax-xmin,
+        height: ymax-ymin
+        };
+    };
+
+// Return whether a point is inside, on, or outside the cell:
+//   -1: point is outside the perimeter of the cell
+//    0: point is on the perimeter of the cell
+//    1: point is inside the perimeter of the cell
+//
+Voronoi.prototype.Cell.prototype.pointIntersection = function(x, y) {
+    // Check if point in polygon. Since all polygons of a Voronoi
+    // diagram are convex, then:
+    // http://paulbourke.net/geometry/polygonmesh/
+    // Solution 3 (2D):
+    //   "If the polygon is convex then one can consider the polygon
+    //   "as a 'path' from the first vertex. A point is on the interior
+    //   "of this polygons if it is always on the same side of all the
+    //   "line segments making up the path. ...
+    //   "(y - y0) (x1 - x0) - (x - x0) (y1 - y0)
+    //   "if it is less than 0 then P is to the right of the line segment,
+    //   "if greater than 0 it is to the left, if equal to 0 then it lies
+    //   "on the line segment"
+    var halfedges = this.halfedges,
+        iHalfedge = halfedges.length,
+        halfedge,
+        p0, p1, r;
+    while (iHalfedge--) {
+        halfedge = halfedges[iHalfedge];
+        p0 = halfedge.getStartpoint();
+        p1 = halfedge.getEndpoint();
+        r = (y-p0.y)*(p1.x-p0.x)-(x-p0.x)*(p1.y-p0.y);
+        if (!r) {
+            return 0;
+            }
+        if (r > 0) {
+            return -1;
+            }
+        }
+    return 1;
+    };
+
+// ---------------------------------------------------------------------------
+// Edge methods
+//
+
+Voronoi.prototype.Vertex = function(x, y) {
+    this.x = x;
+    this.y = y;
+    };
+
+Voronoi.prototype.Edge = function(lSite, rSite) {
+    this.lSite = lSite;
+    this.rSite = rSite;
+    this.va = this.vb = null;
+    };
+
+Voronoi.prototype.Halfedge = function(edge, lSite, rSite) {
+    this.site = lSite;
+    this.edge = edge;
+    // 'angle' is a value to be used for properly sorting the
+    // halfsegments counterclockwise. By convention, we will
+    // use the angle of the line defined by the 'site to the left'
+    // to the 'site to the right'.
+    // However, border edges have no 'site to the right': thus we
+    // use the angle of line perpendicular to the halfsegment (the
+    // edge should have both end points defined in such case.)
+    if (rSite) {
+        this.angle = Math.atan2(rSite.y-lSite.y, rSite.x-lSite.x);
+        }
+    else {
+        var va = edge.va,
+            vb = edge.vb;
+        // rhill 2011-05-31: used to call getStartpoint()/getEndpoint(),
+        // but for performance purpose, these are expanded in place here.
+        this.angle = edge.lSite === lSite ?
+            Math.atan2(vb.x-va.x, va.y-vb.y) :
+            Math.atan2(va.x-vb.x, vb.y-va.y);
+        }
+    };
+
+Voronoi.prototype.createHalfedge = function(edge, lSite, rSite) {
+    return new this.Halfedge(edge, lSite, rSite);
+    };
+
+Voronoi.prototype.Halfedge.prototype.getStartpoint = function() {
+    return this.edge.lSite === this.site ? this.edge.va : this.edge.vb;
+    };
+
+Voronoi.prototype.Halfedge.prototype.getEndpoint = function() {
+    return this.edge.lSite === this.site ? this.edge.vb : this.edge.va;
+    };
+
+
+
+// this create and add a vertex to the internal collection
+
+Voronoi.prototype.createVertex = function(x, y) {
+    var v = this.vertexJunkyard.pop();
+    if ( !v ) {
+        v = new this.Vertex(x, y);
+        }
+    else {
+        v.x = x;
+        v.y = y;
+        }
+    this.vertices.push(v);
+    return v;
+    };
+
+// this create and add an edge to internal collection, and also create
+// two halfedges which are added to each site's counterclockwise array
+// of halfedges.
+
+Voronoi.prototype.createEdge = function(lSite, rSite, va, vb) {
+    var edge = this.edgeJunkyard.pop();
+    if ( !edge ) {
+        edge = new this.Edge(lSite, rSite);
+        }
+    else {
+        edge.lSite = lSite;
+        edge.rSite = rSite;
+        edge.va = edge.vb = null;
+        }
+
+    this.edges.push(edge);
+    if (va) {
+        this.setEdgeStartpoint(edge, lSite, rSite, va);
+        }
+    if (vb) {
+        this.setEdgeEndpoint(edge, lSite, rSite, vb);
+        }
+    this.cells[lSite.voronoiId].halfedges.push(this.createHalfedge(edge, lSite, rSite));
+    this.cells[rSite.voronoiId].halfedges.push(this.createHalfedge(edge, rSite, lSite));
+    return edge;
+    };
+
+Voronoi.prototype.createBorderEdge = function(lSite, va, vb) {
+    var edge = this.edgeJunkyard.pop();
+    if ( !edge ) {
+        edge = new this.Edge(lSite, null);
+        }
+    else {
+        edge.lSite = lSite;
+        edge.rSite = null;
+        }
+    edge.va = va;
+    edge.vb = vb;
+    this.edges.push(edge);
+    return edge;
+    };
+
+Voronoi.prototype.setEdgeStartpoint = function(edge, lSite, rSite, vertex) {
+    if (!edge.va && !edge.vb) {
+        edge.va = vertex;
+        edge.lSite = lSite;
+        edge.rSite = rSite;
+        }
+    else if (edge.lSite === rSite) {
+        edge.vb = vertex;
+        }
+    else {
+        edge.va = vertex;
+        }
+    };
+
+Voronoi.prototype.setEdgeEndpoint = function(edge, lSite, rSite, vertex) {
+    this.setEdgeStartpoint(edge, rSite, lSite, vertex);
+    };
+
+// ---------------------------------------------------------------------------
+// Beachline methods
+
+// rhill 2011-06-07: For some reasons, performance suffers significantly
+// when instanciating a literal object instead of an empty ctor
+Voronoi.prototype.Beachsection = function() {
+    };
+
+// rhill 2011-06-02: A lot of Beachsection instanciations
+// occur during the computation of the Voronoi diagram,
+// somewhere between the number of sites and twice the
+// number of sites, while the number of Beachsections on the
+// beachline at any given time is comparatively low. For this
+// reason, we reuse already created Beachsections, in order
+// to avoid new memory allocation. This resulted in a measurable
+// performance gain.
+
+Voronoi.prototype.createBeachsection = function(site) {
+    var beachsection = this.beachsectionJunkyard.pop();
+    if (!beachsection) {
+        beachsection = new this.Beachsection();
+        }
+    beachsection.site = site;
+    return beachsection;
+    };
+
+// calculate the left break point of a particular beach section,
+// given a particular sweep line
+Voronoi.prototype.leftBreakPoint = function(arc, directrix) {
+    // http://en.wikipedia.org/wiki/Parabola
+    // http://en.wikipedia.org/wiki/Quadratic_equation
+    // h1 = x1,
+    // k1 = (y1+directrix)/2,
+    // h2 = x2,
+    // k2 = (y2+directrix)/2,
+    // p1 = k1-directrix,
+    // a1 = 1/(4*p1),
+    // b1 = -h1/(2*p1),
+    // c1 = h1*h1/(4*p1)+k1,
+    // p2 = k2-directrix,
+    // a2 = 1/(4*p2),
+    // b2 = -h2/(2*p2),
+    // c2 = h2*h2/(4*p2)+k2,
+    // x = (-(b2-b1) + Math.sqrt((b2-b1)*(b2-b1) - 4*(a2-a1)*(c2-c1))) / (2*(a2-a1))
+    // When x1 become the x-origin:
+    // h1 = 0,
+    // k1 = (y1+directrix)/2,
+    // h2 = x2-x1,
+    // k2 = (y2+directrix)/2,
+    // p1 = k1-directrix,
+    // a1 = 1/(4*p1),
+    // b1 = 0,
+    // c1 = k1,
+    // p2 = k2-directrix,
+    // a2 = 1/(4*p2),
+    // b2 = -h2/(2*p2),
+    // c2 = h2*h2/(4*p2)+k2,
+    // x = (-b2 + Math.sqrt(b2*b2 - 4*(a2-a1)*(c2-k1))) / (2*(a2-a1)) + x1
+
+    // change code below at your own risk: care has been taken to
+    // reduce errors due to computers' finite arithmetic precision.
+    // Maybe can still be improved, will see if any more of this
+    // kind of errors pop up again.
+    var site = arc.site,
+        rfocx = site.x,
+        rfocy = site.y,
+        pby2 = rfocy-directrix;
+    // parabola in degenerate case where focus is on directrix
+    if (!pby2) {
+        return rfocx;
+        }
+    var lArc = arc.rbPrevious;
+    if (!lArc) {
+        return -Infinity;
+        }
+    site = lArc.site;
+    var lfocx = site.x,
+        lfocy = site.y,
+        plby2 = lfocy-directrix;
+    // parabola in degenerate case where focus is on directrix
+    if (!plby2) {
+        return lfocx;
+        }
+    var hl = lfocx-rfocx,
+        aby2 = 1/pby2-1/plby2,
+        b = hl/plby2;
+    if (aby2) {
+        return (-b+this.sqrt(b*b-2*aby2*(hl*hl/(-2*plby2)-lfocy+plby2/2+rfocy-pby2/2)))/aby2+rfocx;
+        }
+    // both parabolas have same distance to directrix, thus break point is midway
+    return (rfocx+lfocx)/2;
+    };
+
+// calculate the right break point of a particular beach section,
+// given a particular directrix
+Voronoi.prototype.rightBreakPoint = function(arc, directrix) {
+    var rArc = arc.rbNext;
+    if (rArc) {
+        return this.leftBreakPoint(rArc, directrix);
+        }
+    var site = arc.site;
+    return site.y === directrix ? site.x : Infinity;
+    };
+
+Voronoi.prototype.detachBeachsection = function(beachsection) {
+    this.detachCircleEvent(beachsection); // detach potentially attached circle event
+    this.beachline.rbRemoveNode(beachsection); // remove from RB-tree
+    this.beachsectionJunkyard.push(beachsection); // mark for reuse
+    };
+
+Voronoi.prototype.removeBeachsection = function(beachsection) {
+    var circle = beachsection.circleEvent,
+        x = circle.x,
+        y = circle.ycenter,
+        vertex = this.createVertex(x, y),
+        previous = beachsection.rbPrevious,
+        next = beachsection.rbNext,
+        disappearingTransitions = [beachsection],
+        abs_fn = Math.abs;
+
+    // remove collapsed beachsection from beachline
+    this.detachBeachsection(beachsection);
+
+    // there could be more than one empty arc at the deletion point, this
+    // happens when more than two edges are linked by the same vertex,
+    // so we will collect all those edges by looking up both sides of
+    // the deletion point.
+    // by the way, there is *always* a predecessor/successor to any collapsed
+    // beach section, it's just impossible to have a collapsing first/last
+    // beach sections on the beachline, since they obviously are unconstrained
+    // on their left/right side.
+
+    // look left
+    var lArc = previous;
+    while (lArc.circleEvent && abs_fn(x-lArc.circleEvent.x)<1e-9 && abs_fn(y-lArc.circleEvent.ycenter)<1e-9) {
+        previous = lArc.rbPrevious;
+        disappearingTransitions.unshift(lArc);
+        this.detachBeachsection(lArc); // mark for reuse
+        lArc = previous;
+        }
+    // even though it is not disappearing, I will also add the beach section
+    // immediately to the left of the left-most collapsed beach section, for
+    // convenience, since we need to refer to it later as this beach section
+    // is the 'left' site of an edge for which a start point is set.
+    disappearingTransitions.unshift(lArc);
+    this.detachCircleEvent(lArc);
+
+    // look right
+    var rArc = next;
+    while (rArc.circleEvent && abs_fn(x-rArc.circleEvent.x)<1e-9 && abs_fn(y-rArc.circleEvent.ycenter)<1e-9) {
+        next = rArc.rbNext;
+        disappearingTransitions.push(rArc);
+        this.detachBeachsection(rArc); // mark for reuse
+        rArc = next;
+        }
+    // we also have to add the beach section immediately to the right of the
+    // right-most collapsed beach section, since there is also a disappearing
+    // transition representing an edge's start point on its left.
+    disappearingTransitions.push(rArc);
+    this.detachCircleEvent(rArc);
+
+    // walk through all the disappearing transitions between beach sections and
+    // set the start point of their (implied) edge.
+    var nArcs = disappearingTransitions.length,
+        iArc;
+    for (iArc=1; iArc<nArcs; iArc++) {
+        rArc = disappearingTransitions[iArc];
+        lArc = disappearingTransitions[iArc-1];
+        this.setEdgeStartpoint(rArc.edge, lArc.site, rArc.site, vertex);
+        }
+
+    // create a new edge as we have now a new transition between
+    // two beach sections which were previously not adjacent.
+    // since this edge appears as a new vertex is defined, the vertex
+    // actually define an end point of the edge (relative to the site
+    // on the left)
+    lArc = disappearingTransitions[0];
+    rArc = disappearingTransitions[nArcs-1];
+    rArc.edge = this.createEdge(lArc.site, rArc.site, undefined, vertex);
+
+    // create circle events if any for beach sections left in the beachline
+    // adjacent to collapsed sections
+    this.attachCircleEvent(lArc);
+    this.attachCircleEvent(rArc);
+    };
+
+Voronoi.prototype.addBeachsection = function(site) {
+    var x = site.x,
+        directrix = site.y;
+
+    // find the left and right beach sections which will surround the newly
+    // created beach section.
+    // rhill 2011-06-01: This loop is one of the most often executed,
+    // hence we expand in-place the comparison-against-epsilon calls.
+    var lArc, rArc,
+        dxl, dxr,
+        node = this.beachline.root;
+
+    while (node) {
+        dxl = this.leftBreakPoint(node,directrix)-x;
+        // x lessThanWithEpsilon xl => falls somewhere before the left edge of the beachsection
+        if (dxl > 1e-9) {
+            // this case should never happen
+            // if (!node.rbLeft) {
+            //    rArc = node.rbLeft;
+            //    break;
+            //    }
+            node = node.rbLeft;
+            }
+        else {
+            dxr = x-this.rightBreakPoint(node,directrix);
+            // x greaterThanWithEpsilon xr => falls somewhere after the right edge of the beachsection
+            if (dxr > 1e-9) {
+                if (!node.rbRight) {
+                    lArc = node;
+                    break;
+                    }
+                node = node.rbRight;
+                }
+            else {
+                // x equalWithEpsilon xl => falls exactly on the left edge of the beachsection
+                if (dxl > -1e-9) {
+                    lArc = node.rbPrevious;
+                    rArc = node;
+                    }
+                // x equalWithEpsilon xr => falls exactly on the right edge of the beachsection
+                else if (dxr > -1e-9) {
+                    lArc = node;
+                    rArc = node.rbNext;
+                    }
+                // falls exactly somewhere in the middle of the beachsection
+                else {
+                    lArc = rArc = node;
+                    }
+                break;
+                }
+            }
+        }
+    // at this point, keep in mind that lArc and/or rArc could be
+    // undefined or null.
+
+    // create a new beach section object for the site and add it to RB-tree
+    var newArc = this.createBeachsection(site);
+    this.beachline.rbInsertSuccessor(lArc, newArc);
+
+    // cases:
+    //
+
+    // [null,null]
+    // least likely case: new beach section is the first beach section on the
+    // beachline.
+    // This case means:
+    //   no new transition appears
+    //   no collapsing beach section
+    //   new beachsection become root of the RB-tree
+    if (!lArc && !rArc) {
+        return;
+        }
+
+    // [lArc,rArc] where lArc == rArc
+    // most likely case: new beach section split an existing beach
+    // section.
+    // This case means:
+    //   one new transition appears
+    //   the left and right beach section might be collapsing as a result
+    //   two new nodes added to the RB-tree
+    if (lArc === rArc) {
+        // invalidate circle event of split beach section
+        this.detachCircleEvent(lArc);
+
+        // split the beach section into two separate beach sections
+        rArc = this.createBeachsection(lArc.site);
+        this.beachline.rbInsertSuccessor(newArc, rArc);
+
+        // since we have a new transition between two beach sections,
+        // a new edge is born
+        newArc.edge = rArc.edge = this.createEdge(lArc.site, newArc.site);
+
+        // check whether the left and right beach sections are collapsing
+        // and if so create circle events, to be notified when the point of
+        // collapse is reached.
+        this.attachCircleEvent(lArc);
+        this.attachCircleEvent(rArc);
+        return;
+        }
+
+    // [lArc,null]
+    // even less likely case: new beach section is the *last* beach section
+    // on the beachline -- this can happen *only* if *all* the previous beach
+    // sections currently on the beachline share the same y value as
+    // the new beach section.
+    // This case means:
+    //   one new transition appears
+    //   no collapsing beach section as a result
+    //   new beach section become right-most node of the RB-tree
+    if (lArc && !rArc) {
+        newArc.edge = this.createEdge(lArc.site,newArc.site);
+        return;
+        }
+
+    // [null,rArc]
+    // impossible case: because sites are strictly processed from top to bottom,
+    // and left to right, which guarantees that there will always be a beach section
+    // on the left -- except of course when there are no beach section at all on
+    // the beach line, which case was handled above.
+    // rhill 2011-06-02: No point testing in non-debug version
+    //if (!lArc && rArc) {
+    //    throw "Voronoi.addBeachsection(): What is this I don't even";
+    //    }
+
+    // [lArc,rArc] where lArc != rArc
+    // somewhat less likely case: new beach section falls *exactly* in between two
+    // existing beach sections
+    // This case means:
+    //   one transition disappears
+    //   two new transitions appear
+    //   the left and right beach section might be collapsing as a result
+    //   only one new node added to the RB-tree
+    if (lArc !== rArc) {
+        // invalidate circle events of left and right sites
+        this.detachCircleEvent(lArc);
+        this.detachCircleEvent(rArc);
+
+        // an existing transition disappears, meaning a vertex is defined at
+        // the disappearance point.
+        // since the disappearance is caused by the new beachsection, the
+        // vertex is at the center of the circumscribed circle of the left,
+        // new and right beachsections.
+        // http://mathforum.org/library/drmath/view/55002.html
+        // Except that I bring the origin at A to simplify
+        // calculation
+        var lSite = lArc.site,
+            ax = lSite.x,
+            ay = lSite.y,
+            bx=site.x-ax,
+            by=site.y-ay,
+            rSite = rArc.site,
+            cx=rSite.x-ax,
+            cy=rSite.y-ay,
+            d=2*(bx*cy-by*cx),
+            hb=bx*bx+by*by,
+            hc=cx*cx+cy*cy,
+            vertex = this.createVertex((cy*hb-by*hc)/d+ax, (bx*hc-cx*hb)/d+ay);
+
+        // one transition disappear
+        this.setEdgeStartpoint(rArc.edge, lSite, rSite, vertex);
+
+        // two new transitions appear at the new vertex location
+        newArc.edge = this.createEdge(lSite, site, undefined, vertex);
+        rArc.edge = this.createEdge(site, rSite, undefined, vertex);
+
+        // check whether the left and right beach sections are collapsing
+        // and if so create circle events, to handle the point of collapse.
+        this.attachCircleEvent(lArc);
+        this.attachCircleEvent(rArc);
+        return;
+        }
+    };
+
+// ---------------------------------------------------------------------------
+// Circle event methods
+
+// rhill 2011-06-07: For some reasons, performance suffers significantly
+// when instanciating a literal object instead of an empty ctor
+Voronoi.prototype.CircleEvent = function() {
+    // rhill 2013-10-12: it helps to state exactly what we are at ctor time.
+    this.arc = null;
+    this.rbLeft = null;
+    this.rbNext = null;
+    this.rbParent = null;
+    this.rbPrevious = null;
+    this.rbRed = false;
+    this.rbRight = null;
+    this.site = null;
+    this.x = this.y = this.ycenter = 0;
+    };
+
+Voronoi.prototype.attachCircleEvent = function(arc) {
+    var lArc = arc.rbPrevious,
+        rArc = arc.rbNext;
+    if (!lArc || !rArc) {return;} // does that ever happen?
+    var lSite = lArc.site,
+        cSite = arc.site,
+        rSite = rArc.site;
+
+    // If site of left beachsection is same as site of
+    // right beachsection, there can't be convergence
+    if (lSite===rSite) {return;}
+
+    // Find the circumscribed circle for the three sites associated
+    // with the beachsection triplet.
+    // rhill 2011-05-26: It is more efficient to calculate in-place
+    // rather than getting the resulting circumscribed circle from an
+    // object returned by calling Voronoi.circumcircle()
+    // http://mathforum.org/library/drmath/view/55002.html
+    // Except that I bring the origin at cSite to simplify calculations.
+    // The bottom-most part of the circumcircle is our Fortune 'circle
+    // event', and its center is a vertex potentially part of the final
+    // Voronoi diagram.
+    var bx = cSite.x,
+        by = cSite.y,
+        ax = lSite.x-bx,
+        ay = lSite.y-by,
+        cx = rSite.x-bx,
+        cy = rSite.y-by;
+
+    // If points l->c->r are clockwise, then center beach section does not
+    // collapse, hence it can't end up as a vertex (we reuse 'd' here, which
+    // sign is reverse of the orientation, hence we reverse the test.
+    // http://en.wikipedia.org/wiki/Curve_orientation#Orientation_of_a_simple_polygon
+    // rhill 2011-05-21: Nasty finite precision error which caused circumcircle() to
+    // return infinites: 1e-12 seems to fix the problem.
+    var d = 2*(ax*cy-ay*cx);
+    if (d >= -2e-12){return;}
+
+    var ha = ax*ax+ay*ay,
+        hc = cx*cx+cy*cy,
+        x = (cy*ha-ay*hc)/d,
+        y = (ax*hc-cx*ha)/d,
+        ycenter = y+by;
+
+    // Important: ybottom should always be under or at sweep, so no need
+    // to waste CPU cycles by checking
+
+    // recycle circle event object if possible
+    var circleEvent = this.circleEventJunkyard.pop();
+    if (!circleEvent) {
+        circleEvent = new this.CircleEvent();
+        }
+    circleEvent.arc = arc;
+    circleEvent.site = cSite;
+    circleEvent.x = x+bx;
+    circleEvent.y = ycenter+this.sqrt(x*x+y*y); // y bottom
+    circleEvent.ycenter = ycenter;
+    arc.circleEvent = circleEvent;
+
+    // find insertion point in RB-tree: circle events are ordered from
+    // smallest to largest
+    var predecessor = null,
+        node = this.circleEvents.root;
+    while (node) {
+        if (circleEvent.y < node.y || (circleEvent.y === node.y && circleEvent.x <= node.x)) {
+            if (node.rbLeft) {
+                node = node.rbLeft;
+                }
+            else {
+                predecessor = node.rbPrevious;
+                break;
+                }
+            }
+        else {
+            if (node.rbRight) {
+                node = node.rbRight;
+                }
+            else {
+                predecessor = node;
+                break;
+                }
+            }
+        }
+    this.circleEvents.rbInsertSuccessor(predecessor, circleEvent);
+    if (!predecessor) {
+        this.firstCircleEvent = circleEvent;
+        }
+    };
+
+Voronoi.prototype.detachCircleEvent = function(arc) {
+    var circleEvent = arc.circleEvent;
+    if (circleEvent) {
+        if (!circleEvent.rbPrevious) {
+            this.firstCircleEvent = circleEvent.rbNext;
+            }
+        this.circleEvents.rbRemoveNode(circleEvent); // remove from RB-tree
+        this.circleEventJunkyard.push(circleEvent);
+        arc.circleEvent = null;
+        }
+    };
+
+// ---------------------------------------------------------------------------
+// Diagram completion methods
+
+// connect dangling edges (not if a cursory test tells us
+// it is not going to be visible.
+// return value:
+//   false: the dangling endpoint couldn't be connected
+//   true: the dangling endpoint could be connected
+Voronoi.prototype.connectEdge = function(edge, bbox) {
+    // skip if end point already connected
+    var vb = edge.vb;
+    if (!!vb) {return true;}
+
+    // make local copy for performance purpose
+    var va = edge.va,
+        xl = bbox.xl,
+        xr = bbox.xr,
+        yt = bbox.yt,
+        yb = bbox.yb,
+        lSite = edge.lSite,
+        rSite = edge.rSite,
+        lx = lSite.x,
+        ly = lSite.y,
+        rx = rSite.x,
+        ry = rSite.y,
+        fx = (lx+rx)/2,
+        fy = (ly+ry)/2,
+        fm, fb;
+
+    // if we reach here, this means cells which use this edge will need
+    // to be closed, whether because the edge was removed, or because it
+    // was connected to the bounding box.
+    this.cells[lSite.voronoiId].closeMe = true;
+    this.cells[rSite.voronoiId].closeMe = true;
+
+    // get the line equation of the bisector if line is not vertical
+    if (ry !== ly) {
+        fm = (lx-rx)/(ry-ly);
+        fb = fy-fm*fx;
+        }
+
+    // remember, direction of line (relative to left site):
+    // upward: left.x < right.x
+    // downward: left.x > right.x
+    // horizontal: left.x == right.x
+    // upward: left.x < right.x
+    // rightward: left.y < right.y
+    // leftward: left.y > right.y
+    // vertical: left.y == right.y
+
+    // depending on the direction, find the best side of the
+    // bounding box to use to determine a reasonable start point
+
+    // rhill 2013-12-02:
+    // While at it, since we have the values which define the line,
+    // clip the end of va if it is outside the bbox.
+    // https://github.com/gorhill/Javascript-Voronoi/issues/15
+    // TODO: Do all the clipping here rather than rely on Liang-Barsky
+    // which does not do well sometimes due to loss of arithmetic
+    // precision. The code here doesn't degrade if one of the vertex is
+    // at a huge distance.
+
+    // special case: vertical line
+    if (fm === undefined) {
+        // doesn't intersect with viewport
+        if (fx < xl || fx >= xr) {return false;}
+        // downward
+        if (lx > rx) {
+            if (!va || va.y < yt) {
+                va = this.createVertex(fx, yt);
+                }
+            else if (va.y >= yb) {
+                return false;
+                }
+            vb = this.createVertex(fx, yb);
+            }
+        // upward
+        else {
+            if (!va || va.y > yb) {
+                va = this.createVertex(fx, yb);
+                }
+            else if (va.y < yt) {
+                return false;
+                }
+            vb = this.createVertex(fx, yt);
+            }
+        }
+    // closer to vertical than horizontal, connect start point to the
+    // top or bottom side of the bounding box
+    else if (fm < -1 || fm > 1) {
+        // downward
+        if (lx > rx) {
+            if (!va || va.y < yt) {
+                va = this.createVertex((yt-fb)/fm, yt);
+                }
+            else if (va.y >= yb) {
+                return false;
+                }
+            vb = this.createVertex((yb-fb)/fm, yb);
+            }
+        // upward
+        else {
+            if (!va || va.y > yb) {
+                va = this.createVertex((yb-fb)/fm, yb);
+                }
+            else if (va.y < yt) {
+                return false;
+                }
+            vb = this.createVertex((yt-fb)/fm, yt);
+            }
+        }
+    // closer to horizontal than vertical, connect start point to the
+    // left or right side of the bounding box
+    else {
+        // rightward
+        if (ly < ry) {
+            if (!va || va.x < xl) {
+                va = this.createVertex(xl, fm*xl+fb);
+                }
+            else if (va.x >= xr) {
+                return false;
+                }
+            vb = this.createVertex(xr, fm*xr+fb);
+            }
+        // leftward
+        else {
+            if (!va || va.x > xr) {
+                va = this.createVertex(xr, fm*xr+fb);
+                }
+            else if (va.x < xl) {
+                return false;
+                }
+            vb = this.createVertex(xl, fm*xl+fb);
+            }
+        }
+    edge.va = va;
+    edge.vb = vb;
+
+    return true;
+    };
+
+// line-clipping code taken from:
+//   Liang-Barsky function by Daniel White
+//   http://www.skytopia.com/project/articles/compsci/clipping.html
+// Thanks!
+// A bit modified to minimize code paths
+Voronoi.prototype.clipEdge = function(edge, bbox) {
+    var ax = edge.va.x,
+        ay = edge.va.y,
+        bx = edge.vb.x,
+        by = edge.vb.y,
+        t0 = 0,
+        t1 = 1,
+        dx = bx-ax,
+        dy = by-ay;
+    // left
+    var q = ax-bbox.xl;
+    if (dx===0 && q<0) {return false;}
+    var r = -q/dx;
+    if (dx<0) {
+        if (r<t0) {return false;}
+        if (r<t1) {t1=r;}
+        }
+    else if (dx>0) {
+        if (r>t1) {return false;}
+        if (r>t0) {t0=r;}
+        }
+    // right
+    q = bbox.xr-ax;
+    if (dx===0 && q<0) {return false;}
+    r = q/dx;
+    if (dx<0) {
+        if (r>t1) {return false;}
+        if (r>t0) {t0=r;}
+        }
+    else if (dx>0) {
+        if (r<t0) {return false;}
+        if (r<t1) {t1=r;}
+        }
+    // top
+    q = ay-bbox.yt;
+    if (dy===0 && q<0) {return false;}
+    r = -q/dy;
+    if (dy<0) {
+        if (r<t0) {return false;}
+        if (r<t1) {t1=r;}
+        }
+    else if (dy>0) {
+        if (r>t1) {return false;}
+        if (r>t0) {t0=r;}
+        }
+    // bottom        
+    q = bbox.yb-ay;
+    if (dy===0 && q<0) {return false;}
+    r = q/dy;
+    if (dy<0) {
+        if (r>t1) {return false;}
+        if (r>t0) {t0=r;}
+        }
+    else if (dy>0) {
+        if (r<t0) {return false;}
+        if (r<t1) {t1=r;}
+        }
+
+    // if we reach this point, Voronoi edge is within bbox
+
+    // if t0 > 0, va needs to change
+    // rhill 2011-06-03: we need to create a new vertex rather
+    // than modifying the existing one, since the existing
+    // one is likely shared with at least another edge
+    if (t0 > 0) {
+        edge.va = this.createVertex(ax+t0*dx, ay+t0*dy);
+        }
+
+    // if t1 < 1, vb needs to change
+    // rhill 2011-06-03: we need to create a new vertex rather
+    // than modifying the existing one, since the existing
+    // one is likely shared with at least another edge
+    if (t1 < 1) {
+        edge.vb = this.createVertex(ax+t1*dx, ay+t1*dy);
+        }
+
+    // va and/or vb were clipped, thus we will need to close
+    // cells which use this edge.
+    if ( t0 > 0 || t1 < 1 ) {
+        this.cells[edge.lSite.voronoiId].closeMe = true;
+        this.cells[edge.rSite.voronoiId].closeMe = true;
+    }
+
+    return true;
+    };
+
+// Connect/cut edges at bounding box
+Voronoi.prototype.clipEdges = function(bbox) {
+    // connect all dangling edges to bounding box
+    // or get rid of them if it can't be done
+    var edges = this.edges,
+        iEdge = edges.length,
+        edge,
+        abs_fn = Math.abs;
+
+    // iterate backward so we can splice safely
+    while (iEdge--) {
+        edge = edges[iEdge];
+        // edge is removed if:
+        //   it is wholly outside the bounding box
+        //   it is looking more like a point than a line
+        if (!this.connectEdge(edge, bbox) ||
+            !this.clipEdge(edge, bbox) ||
+            (abs_fn(edge.va.x-edge.vb.x)<1e-9 && abs_fn(edge.va.y-edge.vb.y)<1e-9)) {
+            edge.va = edge.vb = null;
+            edges.splice(iEdge,1);
+            }
+        }
+    };
+
+// Close the cells.
+// The cells are bound by the supplied bounding box.
+// Each cell refers to its associated site, and a list
+// of halfedges ordered counterclockwise.
+Voronoi.prototype.closeCells = function(bbox) {
+    var xl = bbox.xl,
+        xr = bbox.xr,
+        yt = bbox.yt,
+        yb = bbox.yb,
+        cells = this.cells,
+        iCell = cells.length,
+        cell,
+        iLeft,
+        halfedges, nHalfedges,
+        edge,
+        va, vb, vz,
+        lastBorderSegment,
+        abs_fn = Math.abs;
+
+    while (iCell--) {
+        cell = cells[iCell];
+        // prune, order halfedges counterclockwise, then add missing ones
+        // required to close cells
+        if (!cell.prepareHalfedges()) {
+            continue;
+            }
+        if (!cell.closeMe) {
+            continue;
+            }
+        // find first 'unclosed' point.
+        // an 'unclosed' point will be the end point of a halfedge which
+        // does not match the start point of the following halfedge
+        halfedges = cell.halfedges;
+        nHalfedges = halfedges.length;
+        // special case: only one site, in which case, the viewport is the cell
+        // ...
+
+        // all other cases
+        iLeft = 0;
+        while (iLeft < nHalfedges) {
+            va = halfedges[iLeft].getEndpoint();
+            vz = halfedges[(iLeft+1) % nHalfedges].getStartpoint();
+            // if end point is not equal to start point, we need to add the missing
+            // halfedge(s) up to vz
+            if (abs_fn(va.x-vz.x)>=1e-9 || abs_fn(va.y-vz.y)>=1e-9) {
+
+                // rhill 2013-12-02:
+                // "Holes" in the halfedges are not necessarily always adjacent.
+                // https://github.com/gorhill/Javascript-Voronoi/issues/16
+
+                // find entry point:
+                switch (true) {
+
+                    // walk downward along left side
+                    case this.equalWithEpsilon(va.x,xl) && this.lessThanWithEpsilon(va.y,yb):
+                        lastBorderSegment = this.equalWithEpsilon(vz.x,xl);
+                        vb = this.createVertex(xl, lastBorderSegment ? vz.y : yb);
+                        edge = this.createBorderEdge(cell.site, va, vb);
+                        iLeft++;
+                        halfedges.splice(iLeft, 0, this.createHalfedge(edge, cell.site, null));
+                        nHalfedges++;
+                        if ( lastBorderSegment ) { break; }
+                        va = vb;
+                        // fall through
+
+                    // walk rightward along bottom side
+                    case this.equalWithEpsilon(va.y,yb) && this.lessThanWithEpsilon(va.x,xr):
+                        lastBorderSegment = this.equalWithEpsilon(vz.y,yb);
+                        vb = this.createVertex(lastBorderSegment ? vz.x : xr, yb);
+                        edge = this.createBorderEdge(cell.site, va, vb);
+                        iLeft++;
+                        halfedges.splice(iLeft, 0, this.createHalfedge(edge, cell.site, null));
+                        nHalfedges++;
+                        if ( lastBorderSegment ) { break; }
+                        va = vb;
+                        // fall through
+
+                    // walk upward along right side
+                    case this.equalWithEpsilon(va.x,xr) && this.greaterThanWithEpsilon(va.y,yt):
+                        lastBorderSegment = this.equalWithEpsilon(vz.x,xr);
+                        vb = this.createVertex(xr, lastBorderSegment ? vz.y : yt);
+                        edge = this.createBorderEdge(cell.site, va, vb);
+                        iLeft++;
+                        halfedges.splice(iLeft, 0, this.createHalfedge(edge, cell.site, null));
+                        nHalfedges++;
+                        if ( lastBorderSegment ) { break; }
+                        va = vb;
+                        // fall through
+
+                    // walk leftward along top side
+                    case this.equalWithEpsilon(va.y,yt) && this.greaterThanWithEpsilon(va.x,xl):
+                        lastBorderSegment = this.equalWithEpsilon(vz.y,yt);
+                        vb = this.createVertex(lastBorderSegment ? vz.x : xl, yt);
+                        edge = this.createBorderEdge(cell.site, va, vb);
+                        iLeft++;
+                        halfedges.splice(iLeft, 0, this.createHalfedge(edge, cell.site, null));
+                        nHalfedges++;
+                        if ( lastBorderSegment ) { break; }
+                        va = vb;
+                        // fall through
+
+                        // walk downward along left side
+                        lastBorderSegment = this.equalWithEpsilon(vz.x,xl);
+                        vb = this.createVertex(xl, lastBorderSegment ? vz.y : yb);
+                        edge = this.createBorderEdge(cell.site, va, vb);
+                        iLeft++;
+                        halfedges.splice(iLeft, 0, this.createHalfedge(edge, cell.site, null));
+                        nHalfedges++;
+                        if ( lastBorderSegment ) { break; }
+                        va = vb;
+                        // fall through
+
+                        // walk rightward along bottom side
+                        lastBorderSegment = this.equalWithEpsilon(vz.y,yb);
+                        vb = this.createVertex(lastBorderSegment ? vz.x : xr, yb);
+                        edge = this.createBorderEdge(cell.site, va, vb);
+                        iLeft++;
+                        halfedges.splice(iLeft, 0, this.createHalfedge(edge, cell.site, null));
+                        nHalfedges++;
+                        if ( lastBorderSegment ) { break; }
+                        va = vb;
+                        // fall through
+
+                        // walk upward along right side
+                        lastBorderSegment = this.equalWithEpsilon(vz.x,xr);
+                        vb = this.createVertex(xr, lastBorderSegment ? vz.y : yt);
+                        edge = this.createBorderEdge(cell.site, va, vb);
+                        iLeft++;
+                        halfedges.splice(iLeft, 0, this.createHalfedge(edge, cell.site, null));
+                        nHalfedges++;
+                        if ( lastBorderSegment ) { break; }
+                        // fall through
+
+                    default:
+                        throw "Voronoi.closeCells() > this makes no sense!";
+                    }
+                }
+            iLeft++;
+            }
+        cell.closeMe = false;
+        }
+    };
+
+// ---------------------------------------------------------------------------
+// Debugging helper
+/*
+Voronoi.prototype.dumpBeachline = function(y) {
+    console.log('Voronoi.dumpBeachline(%f) > Beachsections, from left to right:', y);
+    if ( !this.beachline ) {
+        console.log('  None');
+        }
+    else {
+        var bs = this.beachline.getFirst(this.beachline.root);
+        while ( bs ) {
+            console.log('  site %d: xl: %f, xr: %f', bs.site.voronoiId, this.leftBreakPoint(bs, y), this.rightBreakPoint(bs, y));
+            bs = bs.rbNext;
+            }
+        }
+    };
+*/
+
+// ---------------------------------------------------------------------------
+// Helper: Quantize sites
+
+// rhill 2013-10-12:
+// This is to solve https://github.com/gorhill/Javascript-Voronoi/issues/15
+// Since not all users will end up using the kind of coord values which would
+// cause the issue to arise, I chose to let the user decide whether or not
+// he should sanitize his coord values through this helper. This way, for
+// those users who uses coord values which are known to be fine, no overhead is
+// added.
+
+Voronoi.prototype.quantizeSites = function(sites) {
+    var ε = this.ε,
+        n = sites.length,
+        site;
+    while ( n-- ) {
+        site = sites[n];
+        site.x = Math.floor(site.x / ε) * ε;
+        site.y = Math.floor(site.y / ε) * ε;
+        }
+    };
+
+// ---------------------------------------------------------------------------
+// Helper: Recycle diagram: all vertex, edge and cell objects are
+// "surrendered" to the Voronoi object for reuse.
+// TODO: rhill-voronoi-core v2: more performance to be gained
+// when I change the semantic of what is returned.
+
+Voronoi.prototype.recycle = function(diagram) {
+    if ( diagram ) {
+        if ( diagram instanceof this.Diagram ) {
+            this.toRecycle = diagram;
+            }
+        else {
+            throw 'Voronoi.recycleDiagram() > Need a Diagram object.';
+            }
+        }
+    };
+
+// ---------------------------------------------------------------------------
+// Top-level Fortune loop
+
+// rhill 2011-05-19:
+//   Voronoi sites are kept client-side now, to allow
+//   user to freely modify content. At compute time,
+//   *references* to sites are copied locally.
+
+Voronoi.prototype.compute = function(sites, bbox) {
+    // to measure execution time
+    var startTime = new Date();
+
+    // init internal state
+    this.reset();
+
+    // any diagram data available for recycling?
+    // I do that here so that this is included in execution time
+    if ( this.toRecycle ) {
+        this.vertexJunkyard = this.vertexJunkyard.concat(this.toRecycle.vertices);
+        this.edgeJunkyard = this.edgeJunkyard.concat(this.toRecycle.edges);
+        this.cellJunkyard = this.cellJunkyard.concat(this.toRecycle.cells);
+        this.toRecycle = null;
+        }
+
+    // Initialize site event queue
+    var siteEvents = sites.slice(0);
+    siteEvents.sort(function(a,b){
+        var r = b.y - a.y;
+        if (r) {return r;}
+        return b.x - a.x;
+        });
+
+    // process queue
+    var site = siteEvents.pop(),
+        siteid = 0,
+        xsitex, // to avoid duplicate sites
+        xsitey,
+        cells = this.cells,
+        circle;
+
+    // main loop
+    for (;;) {
+        // we need to figure whether we handle a site or circle event
+        // for this we find out if there is a site event and it is
+        // 'earlier' than the circle event
+        circle = this.firstCircleEvent;
+
+        // add beach section
+        if (site && (!circle || site.y < circle.y || (site.y === circle.y && site.x < circle.x))) {
+            // only if site is not a duplicate
+            if (site.x !== xsitex || site.y !== xsitey) {
+                // first create cell for new site
+                cells[siteid] = this.createCell(site);
+                site.voronoiId = siteid++;
+                // then create a beachsection for that site
+                this.addBeachsection(site);
+                // remember last site coords to detect duplicate
+                xsitey = site.y;
+                xsitex = site.x;
+                }
+            site = siteEvents.pop();
+            }
+
+        // remove beach section
+        else if (circle) {
+            this.removeBeachsection(circle.arc);
+            }
+
+        // all done, quit
+        else {
+            break;
+            }
+        }
+
+    // wrapping-up:
+    //   connect dangling edges to bounding box
+    //   cut edges as per bounding box
+    //   discard edges completely outside bounding box
+    //   discard edges which are point-like
+    this.clipEdges(bbox);
+
+    //   add missing edges in order to close opened cells
+    this.closeCells(bbox);
+
+    // to measure execution time
+    var stopTime = new Date();
+
+    // prepare return values
+    var diagram = new this.Diagram();
+    diagram.cells = this.cells;
+    diagram.edges = this.edges;
+    diagram.vertices = this.vertices;
+    diagram.execTime = stopTime.getTime()-startTime.getTime();
+
+    // clean up
+    this.reset();
+
+    return diagram;
+    };
+
+/******************************************************************************/
+
+// stuff below here was modified by sanine
+export default Voronoi;