Calculate same-layer crossings

lib/order/cross-count.js

@@ -22,8 +22,34 @@ module.exports = crossCount;
  */
 function crossCount(g, layering) {
   var cc = 0;
-  for (var i = 1; i < layering.length; ++i) {
-    cc += twoLayerCrossCount(g, layering[i-1], layering[i]);
+  for (var i = 0; i < layering.length; ++i) {
+    cc += singleLayerCrossCount(g, layering[i]);
+    if (i > 0) {
+      cc += twoLayerCrossCount(g, layering[i-1], layering[i]);
+    }
+  }
+  return cc;
+}
+
+function singleLayerCrossCount(g, layer) {
+  var cc = 0;
+  if (layer.length) {
+    var layerRank = g.node(layer[0]).rank;
+    var layerIndex = _.zipObject(
+      layer,
+       _.map(layer, function (v, i) { return i; })
+    );
+
+    _.forEach(layer, function(n, i) {
+      _.forEach(g.inEdges(n), function(e) {
+        if (g.node(e.v).rank == layerRank) {
+          var otherPos = layerIndex[e.v];
+          if (Math.abs(otherPos - i) > 1) {
+            cc++;
+          }
+        }
+      });
+    });
   }
   return cc;
 }