Draggable: Don't cache parent offset if the parent position is fixed.…

… Fixes #5009 - Draggable: scroll not working with parent's position fixed

tests/unit/draggable/draggable_core.js

@@ -129,4 +129,34 @@ test( "#6258: not following mouse when scrolled and using overflow-y: scroll", f
 		});
 });
 
+test( "#5009: scroll not working with parent's position fixed", function() {
+	expect( 2 );
+
+	var startValue = 300,
+		element = $( "#draggable1" ).wrap( "<div id='wrapper' />" ).draggable({
+			drag: function() {
+				startValue += 100;
+				$( document ).scrollTop( startValue ).scrollLeft( startValue );
+			},
+			stop: function( event, ui ) {
+				equal( ui.position.left, 10, "left position is correct despite overflow on HTML" );
+				equal( ui.position.top, 10, "top position is correct despite overflow on HTML" );
+				$( document ).scrollTop( 0 ).scrollLeft( 0 );
+			}
+		}),
+		contentToForceScroll = $( "<div>" ).css({
+			height: "20000px",
+			width: "20000px"
+		});
+
+	$( "#qunit-fixture" ).append( contentToForceScroll );
+	$( "#wrapper" ).css( "position", "fixed" );
+
+	element.simulate( "drag", {
+		dx: 10,
+		dy: 10,
+		moves: 3
+	});
+});
+
 })( jQuery );

ui/jquery.ui.draggable.js

@@ -125,8 +125,10 @@ $.widget("ui.draggable", $.ui.mouse, {
 		this._cacheMargins();
 
 		//Store the helper's css position
-		this.cssPosition = this.helper.css("position");
+		this.cssPosition = this.helper.css( "position" );
 		this.scrollParent = this.helper.scrollParent();
+		this.offsetParent = this.helper.offsetParent();
+		this.offsetParentCssPosition = this.offsetParent.css( "position" );
 
 		//The element's absolute position on the page minus margins
 		this.offset = this.positionAbs = this.element.offset();
@@ -184,6 +186,10 @@ $.widget("ui.draggable", $.ui.mouse, {
 	},
 
 	_mouseDrag: function(event, noPropagation) {
+		// reset any necessary cached properties (see #5009)
+		if ( this.offsetParentCssPosition === "fixed" ) {
+			this.offset.parent = this._getParentOffset();
+		}
 
 		//Compute the helpers position
 		this.position = this._generatePosition(event);
@@ -320,7 +326,6 @@ $.widget("ui.draggable", $.ui.mouse, {
 	_getParentOffset: function() {
 
 		//Get the offsetParent and cache its position
-		this.offsetParent = this.helper.offsetParent();
 		var po = this.offsetParent.offset();
 
 		// This is a special case where we need to modify a offset calculated on start, since the following happened: