Add a faster and more accurate level size calculation to the tree. This (hopefully) fixes the problems with super wide trees in prod.

static/js/graphing.js

@@ -377,6 +377,23 @@ ImageHistoryTree.prototype.expandCollapsed_ = function(imageNode) {
 };
 
 
+/**
+ * Returns the level of the node in the tree. Recursively computes and updates
+ * if necessary.
+ */
+ImageHistoryTree.prototype.calculateLevel_ = function(node) {
+  if (node['level'] != null) {
+    return node['level'];
+  }
+
+  if (node['parent'] == null) {
+    return node['level'] = 0;
+  }
+
+  return node['level'] = (this.calculateLevel_(node['parent']) + 1);
+};
+
+
 /**
  * Builds the root node for the tree.
  */
@@ -392,11 +409,16 @@ ImageHistoryTree.prototype.buildRoot_ = function() {
   var imageByDockerId = {};
   for (var i = 0; i < this.images_.length; ++i) {
     var image = this.images_[i];
+
+    // Skip images that are currently uploading.
+    if (image.uploading) { continue; }
+
     var imageNode = {
       "name": image.id.substr(0, 12),
       "children": [],
       "image": image,
-      "tags": image.tags
+      "tags": image.tags,
+      "level": null
     };
     imageByDockerId[image.id] = imageNode;
   }
@@ -405,6 +427,7 @@ ImageHistoryTree.prototype.buildRoot_ = function() {
   // For each node, attach it to its immediate parent. If there is no immediate parent,
   // then the node is the root.
   var roots = [];
+  var nodeCountsByLevel = {};
   for (var i = 0; i < this.images_.length; ++i) {
     var image = this.images_[i];
 
@@ -420,10 +443,27 @@ ImageHistoryTree.prototype.buildRoot_ = function() {
       imageNode.parent = parent;
       parent.children.push(imageNode);
     } else {
+      imageNode['level'] = 0;
       roots.push(imageNode);
     }
   }
 
+  // Calculate each node's level.
+  for (var i = 0; i < this.images_.length; ++i) {
+    var image = this.images_[i];
+
+    // Skip images that are currently uploading.
+    if (image.uploading) { continue; }
+
+    var imageNode = imageByDockerId[image.id];
+    var level = this.calculateLevel_(imageNode);
+    if (nodeCountsByLevel[level] == null) {
+      nodeCountsByLevel[level] = 1;
+    } else {
+      nodeCountsByLevel[level]++;
+    }
+  }
+
   // If there are multiple root nodes, then there is at least one branch without shared
   // ancestry and we use the virtual node. Otherwise, we use the root node found.
   var root = {
@@ -438,16 +478,12 @@ ImageHistoryTree.prototype.buildRoot_ = function() {
 
   // Determine the maximum number of nodes at a particular level. This is used to size
   // the width of the tree properly.
-  var maxChildCount = roots.length;
-  for (var i = 0; i < this.images_.length; ++i) {
-    var image = this.images_[i];
-
-    // Skip images that are currently uploading.
-    if (image.uploading) { continue; }
-
-    var imageNode = imageByDockerId[image.id];
-    maxChildCount = Math.max(maxChildCount, this.determineMaximumChildCount_(imageNode));
-  }
+  var maxChildCount = 0;
+  var maxChildHeight = 0;
+  Object.keys(nodeCountsByLevel).forEach(function(key){
+    maxChildCount = Math.max(maxChildCount, nodeCountsByLevel[key]);
+    maxChildHeight = Math.max(maxChildHeight, key);
+  });
 
   // Compact the graph so that any single chain of three (or more) images becomes a collapsed
   // section. We only do this if the max width is > 1 (since for a single width tree, no long
@@ -456,22 +492,21 @@ ImageHistoryTree.prototype.buildRoot_ = function() {
     this.collapseNodes_(root);
   }
 
-  // Determine the maximum height of the tree.
-  var maxHeight = this.determineMaximumHeight_(root);
+  // Determine the maximum height of the tree, with collapsed nodes.
+  var maxCollapsedHeight = this.determineMaximumHeight_(root);
 
   // Finally, set the root node and return.
   this.root_ = root;
 
   return {
     'maxWidth': maxChildCount + 1,
-    'maxHeight': maxHeight
+    'maxHeight': maxCollapsedHeight
   };
 };
 
 
 /**
- * Collapses long single chains of nodes (3 or more) into single nodes to make the graph more
- * compact.
+ * Determines the height of the tree at its longest chain.
  */
 ImageHistoryTree.prototype.determineMaximumHeight_ = function(node) {
   var maxHeight = 0;