Fixup/compensate for chrome zoomed offset bug

src/core.js

@@ -60,7 +60,8 @@ var session = {
 	windowWidth: 0,
 	windowHeight: 0,
 	scrollTop: 0,
-	scrollLeft: 0
+	scrollLeft: 0,
+	chromePatchRefElement: null
 };
 
 /**
@@ -97,6 +98,8 @@ $.fn.powerTip = function(opts, arg) {
 		return $.powerTip[opts].call(targetElements, targetElements, arg);
 	}
 
+	activateChromeZoomedOffsetPatch();
+
 	// extend options
 	options = $.extend({}, $.fn.powerTip.defaults, opts);
 

src/placementcalculator.js

@@ -99,7 +99,7 @@ function PlacementCalculator() {
 	 * @return {Object} An object with the top,left position values.
 	 */
 	function getHtmlPlacement(element, placement) {
-		var objectOffset = element.offset(),
+		var objectOffset = getCompensatedOffset(element),
 			objectWidth = element.outerWidth(),
 			objectHeight = element.outerHeight(),
 			left,
@@ -217,10 +217,10 @@ function PlacementCalculator() {
 			}
 		}
 
-		return {
+		return compensateForZoomBug({
 			top: coords.y + session.scrollTop,
 			left: coords.x + session.scrollLeft
-		};
+		});
 	}
 
 	// expose methods

src/utility.js

@@ -109,7 +109,7 @@ function isMouseOver(element) {
 	// methods do not work with SVG elements
 	// compute width/height because those properties do not exist on the object
 	// returned by getBoundingClientRect() in older versions of IE
-	var elementPosition = element.offset(),
+	var elementPosition = getCompensatedOffset(element),
 		elementBox = element[0].getBoundingClientRect(),
 		elementWidth = elementBox.right - elementBox.left,
 		elementHeight = elementBox.bottom - elementBox.top;
@@ -201,3 +201,55 @@ function countFlags(value) {
 	}
 	return count;
 }
+
+/**
+ * Conditionally make reference for Chrome zoomed offset patch
+ *
+ * Reference https://bugs.chromium.org/p/chromium/issues/detail?id=489206
+ * Suggested patch calls for inserting an absolutely positioned element at 0,0.
+ * However, it appears that document.body serves equally well as a references
+ * and avoid needing to manipulate DOM. Beware offset behavior when body is not
+ * positioned at 0,0.
+ */
+function activateChromeZoomedOffsetPatch() {
+	var style;
+	if (!session.chromePatchRefElement && /Chrome\/[.0-9]*/.test(navigator.userAgent)) {
+		session.chromePatchRefElement = $(document.body);
+		style = {
+			top: 0,
+			left: 0,
+			position: 'absolute',
+			display: 'hidden',
+			height: '1px',
+			margin: 0,
+			width: '1px',
+			zIndex: -1
+		};
+		session.chromePatchRefElement = $('<div/>').css(style).appendTo($(document.body));
+	}
+}
+
+/**
+ * Compensate for the Chrome getBoundingClientRect bug when zoomed.
+ * Reference https://bugs.chromium.org/p/chromium/issues/detail?id=489206
+ * @param {jQuery} element The element that the tooltip should target.
+ * @return {Offsets} The top, left offsets relative to the document.
+ */
+function getCompensatedOffset(element) {
+	return compensateForZoomBug(element.offset());
+}
+
+/**
+ * Compensate for the Chrome measurement bug when zoomed.
+ * @param {object} coords Coordinates to compensate for if zoomed on chrome
+ * @return {Offsets} The top, left offsets relative to the document.
+ */
+function compensateForZoomBug(coords) {
+	if (session.chromePatchRefElement) {
+		var r = session.chromePatchRefElement.offset();
+		coords.top -= r.top;
+		coords.left -= r.left;
+		return coords;
+	}
+	return coords;
+}