Ticket #4377: 4377-offsetparent.patch

Index: /Users/sgonzale/Documents/workspace/jQuery UI/ui/ui.selectable.js
===================================================================
--- /Users/sgonzale/Documents/workspace/jQuery UI/ui/ui.selectable.js	(revision 2470)
+++ /Users/sgonzale/Documents/workspace/jQuery UI/ui/ui.selectable.js	(working copy)
@@ -71,7 +71,11 @@
 		if (this.options.disabled)
 			return;
 
-		var options = this.options;
+		var options = this.options,
+			appendTo = $(options.appendTo),
+			parentOffset = appendTo.css('position') == 'static'
+				? appendTo.offsetParent().offset()
+				: appendTo.offset();
 
 		this.selectees = $(options.filter, this.element[0]);
 
@@ -77,7 +81,7 @@
 
 		this._trigger("start", event);
 
-		$(options.appendTo).append(this.helper);
+		appendTo.append(this.helper);
 		// position helper (lasso)
 		this.helper.css({
 			"z-index": 100,
@@ -82,8 +86,8 @@
 		this.helper.css({
 			"z-index": 100,
 			"position": "absolute",
-			"left": event.clientX,
-			"top": event.clientY,
+			"left": event.clientX-parentOffset.left,
+			"top": event.clientY-parentOffset.top,
 			"width": 0,
 			"height": 0
 		});
@@ -133,10 +137,20 @@
 
 		var options = this.options;
 
-		var x1 = this.opos[0], y1 = this.opos[1], x2 = event.pageX, y2 = event.pageY;
+		var x1 = this.opos[0], y1 = this.opos[1], x2 = event.pageX, y2 = event.pageY,
+			appendTo = $(options.appendTo),
+			parentOffset = appendTo.css('position') == 'static'
+				? appendTo.offsetParent().offset()
+				: appendTo.offset();
+
 		if (x1 > x2) { var tmp = x2; x2 = x1; x1 = tmp; }
 		if (y1 > y2) { var tmp = y2; y2 = y1; y1 = tmp; }
-		this.helper.css({left: x1, top: y1, width: x2-x1, height: y2-y1});
+		this.helper.css({
+			left: x1-parentOffset.left,
+			top: y1-parentOffset.top,
+			width: x2-x1,
+			height: y2-y1
+		});
 
 		this.selectees.each(function() {
 			var selectee = $.data(this, "selectable-item");