From c89d6eac95f75f778ffea3411d1d27e99ede4976 Mon Sep 17 00:00:00 2001
From: Andrew Dupont <prototype@andrewdupont.net>
Date: Fri, 6 Nov 2009 10:58:45 -0600
Subject: [PATCH] Fix incorrect offset in Element.viewportOffset on IE < 8.
 (cherry picked from commit 3afb0002cbd31726187338c5119657b76111f80c)

---
 src/dom/layout.js | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/dom/layout.js b/src/dom/layout.js
index d0d4dca..444da63 100644
--- a/src/dom/layout.js
+++ b/src/dom/layout.js
@@ -751,8 +751,13 @@
     Element.addMethods({
       viewportOffset: function(element) {
         element = $(element);
-        var rect = element.getBoundingClientRect();
-        return new Element.Offset(rect.left, rect.top);
+        var rect  = element.getBoundingClientRect(),
+         docEl = document.documentElement;
+        // The HTML element on IE < 8 has a 2px border by default, giving
+        // an incorrect offset. We correct this by subtracting clientTop
+        // and clientLeft.
+        return new Element.Offset(rect.top - docEl.clientTop,
+         rect.left - docEl.clientLeft);
       },
       
       cumulativeOffset: function(element) {