Calculate same-layer crossings

lib/order/cross-count.js

@@ -22,12 +22,37 @@ 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 layerRank = g.node(layer[0]).rank;
+
+  var layerIndex = _.zipObject(
+    layer,
+     _.map(layer, function (v, i) { return i; })
+  );
+
+  var cc = 0;
+  _.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;
+}
+
 function twoLayerCrossCount(g, northLayer, southLayer) {
   // Sort all of the edges between the north and south layers by their position
   // in the north layer and then the south. Map these edges to the position of