diff -r efd9c589177a -r c0b4a8b5a012 toolkit/javascript/d3/src/layout/force.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/javascript/d3/src/layout/force.js	Thu Apr 10 14:20:23 2014 +0200
@@ -0,0 +1,346 @@
+// A rudimentary force layout using Gauss-Seidel.
+d3.layout.force = function() {
+  var force = {},
+      event = d3.dispatch("tick"),
+      size = [1, 1],
+      drag,
+      alpha,
+      friction = .9,
+      linkDistance = d3_layout_forceLinkDistance,
+      linkStrength = d3_layout_forceLinkStrength,
+      charge = -30,
+      gravity = .1,
+      theta = .8,
+      interval,
+      nodes = [],
+      links = [],
+      distances,
+      strengths,
+      charges;
+
+  function repulse(node) {
+    return function(quad, x1, y1, x2, y2) {
+      if (quad.point !== node) {
+        var dx = quad.cx - node.x,
+            dy = quad.cy - node.y,
+            dn = 1 / Math.sqrt(dx * dx + dy * dy);
+
+        /* Barnes-Hut criterion. */
+        if ((x2 - x1) * dn < theta) {
+          var k = quad.charge * dn * dn;
+          node.px -= dx * k;
+          node.py -= dy * k;
+          return true;
+        }
+
+        if (quad.point && isFinite(dn)) {
+          var k = quad.pointCharge * dn * dn;
+          node.px -= dx * k;
+          node.py -= dy * k;
+        }
+      }
+      return !quad.charge;
+    };
+  }
+
+  function tick() {
+    var n = nodes.length,
+        m = links.length,
+        q,
+        i, // current index
+        o, // current object
+        s, // current source
+        t, // current target
+        l, // current distance
+        k, // current force
+        x, // x-distance
+        y; // y-distance
+
+    // gauss-seidel relaxation for links
+    for (i = 0; i < m; ++i) {
+      o = links[i];
+      s = o.source;
+      t = o.target;
+      x = t.x - s.x;
+      y = t.y - s.y;
+      if (l = (x * x + y * y)) {
+        l = alpha * strengths[i] * ((l = Math.sqrt(l)) - distances[i]) / l;
+        x *= l;
+        y *= l;
+        t.x -= x * (k = s.weight / (t.weight + s.weight));
+        t.y -= y * k;
+        s.x += x * (k = 1 - k);
+        s.y += y * k;
+      }
+    }
+
+    // apply gravity forces
+    if (k = alpha * gravity) {
+      x = size[0] / 2;
+      y = size[1] / 2;
+      i = -1; if (k) while (++i < n) {
+        o = nodes[i];
+        o.x += (x - o.x) * k;
+        o.y += (y - o.y) * k;
+      }
+    }
+
+    // compute quadtree center of mass and apply charge forces
+    if (charge) {
+      d3_layout_forceAccumulate(q = d3.geom.quadtree(nodes), alpha, charges);
+      i = -1; while (++i < n) {
+        if (!(o = nodes[i]).fixed) {
+          q.visit(repulse(o));
+        }
+      }
+    }
+
+    // position verlet integration
+    i = -1; while (++i < n) {
+      o = nodes[i];
+      if (o.fixed) {
+        o.x = o.px;
+        o.y = o.py;
+      } else {
+        o.x -= (o.px - (o.px = o.x)) * friction;
+        o.y -= (o.py - (o.py = o.y)) * friction;
+      }
+    }
+
+    event.tick({type: "tick", alpha: alpha});
+
+    // simulated annealing, basically
+    return (alpha *= .99) < .005;
+  }
+
+  force.on = function(type, listener) {
+    event.on(type, listener);
+    return force;
+  };
+
+  force.nodes = function(x) {
+    if (!arguments.length) return nodes;
+    nodes = x;
+    return force;
+  };
+
+  force.links = function(x) {
+    if (!arguments.length) return links;
+    links = x;
+    return force;
+  };
+
+  force.size = function(x) {
+    if (!arguments.length) return size;
+    size = x;
+    return force;
+  };
+
+  force.linkDistance = function(x) {
+    if (!arguments.length) return linkDistance;
+    linkDistance = d3.functor(x);
+    return force;
+  };
+
+  // For backwards-compatibility.
+  force.distance = force.linkDistance;
+
+  force.linkStrength = function(x) {
+    if (!arguments.length) return linkStrength;
+    linkStrength = d3.functor(x);
+    return force;
+  };
+
+  force.friction = function(x) {
+    if (!arguments.length) return friction;
+    friction = x;
+    return force;
+  };
+
+  force.charge = function(x) {
+    if (!arguments.length) return charge;
+    charge = typeof x === "function" ? x : +x;
+    return force;
+  };
+
+  force.gravity = function(x) {
+    if (!arguments.length) return gravity;
+    gravity = x;
+    return force;
+  };
+
+  force.theta = function(x) {
+    if (!arguments.length) return theta;
+    theta = x;
+    return force;
+  };
+
+  force.start = function() {
+    var i,
+        j,
+        n = nodes.length,
+        m = links.length,
+        w = size[0],
+        h = size[1],
+        neighbors,
+        o;
+
+    for (i = 0; i < n; ++i) {
+      (o = nodes[i]).index = i;
+      o.weight = 0;
+    }
+
+    distances = [];
+    strengths = [];
+    for (i = 0; i < m; ++i) {
+      o = links[i];
+      if (typeof o.source == "number") o.source = nodes[o.source];
+      if (typeof o.target == "number") o.target = nodes[o.target];
+      distances[i] = linkDistance.call(this, o, i);
+      strengths[i] = linkStrength.call(this, o, i);
+      ++o.source.weight;
+      ++o.target.weight;
+    }
+
+    for (i = 0; i < n; ++i) {
+      o = nodes[i];
+      if (isNaN(o.x)) o.x = position("x", w);
+      if (isNaN(o.y)) o.y = position("y", h);
+      if (isNaN(o.px)) o.px = o.x;
+      if (isNaN(o.py)) o.py = o.y;
+    }
+
+    charges = [];
+    if (typeof charge === "function") {
+      for (i = 0; i < n; ++i) {
+        charges[i] = +charge.call(this, nodes[i], i);
+      }
+    } else {
+      for (i = 0; i < n; ++i) {
+        charges[i] = charge;
+      }
+    }
+
+    // initialize node position based on first neighbor
+    function position(dimension, size) {
+      var neighbors = neighbor(i),
+          j = -1,
+          m = neighbors.length,
+          x;
+      while (++j < m) if (!isNaN(x = neighbors[j][dimension])) return x;
+      return Math.random() * size;
+    }
+
+    // initialize neighbors lazily
+    function neighbor() {
+      if (!neighbors) {
+        neighbors = [];
+        for (j = 0; j < n; ++j) {
+          neighbors[j] = [];
+        }
+        for (j = 0; j < m; ++j) {
+          var o = links[j];
+          neighbors[o.source.index].push(o.target);
+          neighbors[o.target.index].push(o.source);
+        }
+      }
+      return neighbors[i];
+    }
+
+    return force.resume();
+  };
+
+  force.resume = function() {
+    alpha = .1;
+    d3.timer(tick);
+    return force;
+  };
+
+  force.stop = function() {
+    alpha = 0;
+    return force;
+  };
+
+  // use `node.call(force.drag)` to make nodes draggable
+  force.drag = function() {
+    if (!drag) drag = d3.behavior.drag()
+        .on("dragstart", dragstart)
+        .on("drag", d3_layout_forceDrag)
+        .on("dragend", d3_layout_forceDragEnd);
+
+    this.on("mouseover.force", d3_layout_forceDragOver)
+        .on("mouseout.force", d3_layout_forceDragOut)
+        .call(drag);
+  };
+
+  function dragstart(d) {
+    d3_layout_forceDragOver(d3_layout_forceDragNode = d);
+    d3_layout_forceDragForce = force;
+  }
+
+  return force;
+};
+
+var d3_layout_forceDragForce,
+    d3_layout_forceDragNode;
+
+function d3_layout_forceDragOver(d) {
+  d.fixed |= 2;
+}
+
+function d3_layout_forceDragOut(d) {
+  if (d !== d3_layout_forceDragNode) d.fixed &= 1;
+}
+
+function d3_layout_forceDragEnd() {
+  d3_layout_forceDrag();
+  d3_layout_forceDragNode.fixed &= 1;
+  d3_layout_forceDragForce = d3_layout_forceDragNode = null;
+}
+
+function d3_layout_forceDrag() {
+  d3_layout_forceDragNode.px += d3.event.dx;
+  d3_layout_forceDragNode.py += d3.event.dy;
+  d3_layout_forceDragForce.resume(); // restart annealing
+}
+
+function d3_layout_forceAccumulate(quad, alpha, charges) {
+  var cx = 0,
+      cy = 0;
+  quad.charge = 0;
+  if (!quad.leaf) {
+    var nodes = quad.nodes,
+        n = nodes.length,
+        i = -1,
+        c;
+    while (++i < n) {
+      c = nodes[i];
+      if (c == null) continue;
+      d3_layout_forceAccumulate(c, alpha, charges);
+      quad.charge += c.charge;
+      cx += c.charge * c.cx;
+      cy += c.charge * c.cy;
+    }
+  }
+  if (quad.point) {
+    // jitter internal nodes that are coincident
+    if (!quad.leaf) {
+      quad.point.x += Math.random() - .5;
+      quad.point.y += Math.random() - .5;
+    }
+    var k = alpha * charges[quad.point.index];
+    quad.charge += quad.pointCharge = k;
+    cx += k * quad.point.x;
+    cy += k * quad.point.y;
+  }
+  quad.cx = cx / quad.charge;
+  quad.cy = cy / quad.charge;
+}
+
+function d3_layout_forceLinkDistance(link) {
+  return 20;
+}
+
+function d3_layout_forceLinkStrength(link) {
+  return 1;
+}