From 869bda649597a5b57f83862e3d93f84d98c62f5f Mon Sep 17 00:00:00 2001
From: Sean Lip <sll@google.com>
Date: Thu, 21 Jul 2016 17:12:10 -0700
Subject: [PATCH] Autoscroll to the current node when the active desc changes.

---
 accessible/tree.service.js | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/accessible/tree.service.js b/accessible/tree.service.js
index b2430aee8..077d062a7 100644
--- a/accessible/tree.service.js
+++ b/accessible/tree.service.js
@@ -144,6 +144,16 @@ blocklyApp.TreeService = ng.core
       this.unmarkActiveDesc_(this.getActiveDescId(treeId));
       this.markActiveDesc_(newActiveDescId);
       this.activeDescendantIds_[treeId] = newActiveDescId;
+
+      // Scroll the new active desc into view, if needed. This has no effect
+      // for blind users, but is helpful for sighted onlookers.
+      var activeDescNode = document.getElementById(newActiveDescId);
+      var documentNode = document.body || document.documentElement;
+      if (activeDescNode.offsetTop < documentNode.scrollTop ||
+          activeDescNode.offsetTop >
+              documentNode.scrollTop + window.innerHeight) {
+        window.scrollTo(0, activeDescNode.offsetTop);
+      }
     },
     getTreeIdForBlock: function(blockId) {
       // Walk up the DOM until we get to the root node of the tree.