Position: Added a check for fraction support in element positions. Fixes #7255 - Position: Revisit solution for off-by-1 errors.

Author: kborchers

tests/unit/position/position_core.js

@@ -406,22 +406,22 @@ test("collision: flip, with margin", function() {
 	}, { top: 0, left: 0 }, "right bottom");
 });
 
-//test('bug #5280: consistent results (avoid fractional values)', function() {
-//	var wrapper = $('#bug-5280'),
-//		elem = wrapper.children(),
-//		offset1 = elem.position({
-//			my: 'center',
-//			at: 'center',
-//			of: wrapper,
-//			collision: 'none'
-//		}).offset(),
-//		offset2 = elem.position({
-//			my: 'center',
-//			at: 'center',
-//			of: wrapper,
-//			collision: 'none'
-//		}).offset();
-//	same(offset1, offset2);
-//});
+test('bug #5280: consistent results (avoid fractional values)', function() {
+	var wrapper = $('#bug-5280'),
+		elem = wrapper.children(),
+		offset1 = elem.position({
+			my: 'center',
+			at: 'center',
+			of: wrapper,
+			collision: 'none'
+		}).offset(),
+		offset2 = elem.position({
+			my: 'center',
+			at: 'center',
+			of: wrapper,
+			collision: 'none'
+		}).offset();
+	same(offset1, offset2);
+});
 
 })(jQuery);

ui/jquery.ui.position.js

@@ -14,6 +14,7 @@ $.ui = $.ui || {};
 var horizontalPositions = /left|center|right/,
 	verticalPositions = /top|center|bottom/,
 	center = "center",
+	support = {},
 	_position = $.fn.position,
 	_offset = $.fn.offset;
 
@@ -121,9 +122,11 @@ $.fn.position = function( options ) {
 			position.top -= elemHeight / 2;
 		}
 
-		// prevent fractions (see #5280)
-		position.left = Math.round( position.left );
-		position.top = Math.round( position.top );
+		// prevent fractions if jQuery version doesn't support them (see #5280)
+		if ( !support.fractions ) {
+			position.left = Math.round( position.left );
+			position.top = Math.round( position.top );
+		}
 
 		collisionPosition = {
 			left: position.left - marginLeft,
@@ -249,4 +252,47 @@ if ( !$.offset.setOffset ) {
 	};
 }
 
+// fraction support test (older versions of jQuery don't support fractions)
+(function () {
+	var body = document.getElementsByTagName( "body" )[ 0 ], 
+		div = document.createElement( "div" ),
+		testElement, testElementParent, testElementStyle, offset, offsetTotal;
+
+	//Create a "fake body" for testing based on method used in jQuery.support
+	testElement = document.createElement( body ? "div" : "body" );
+	testElementStyle = {
+		visibility: "hidden",
+		width: 0,
+		height: 0,
+		border: 0,
+		margin: 0,
+		background: "none"
+	};
+	if ( body ) {
+		jQuery.extend( testElementStyle, {
+			position: "absolute",
+			left: "-1000px",
+			top: "-1000px"
+		});
+	}
+	for ( var i in testElementStyle ) {
+		testElement.style[ i ] = testElementStyle[ i ];
+	}
+	testElement.appendChild( div );
+	testElementParent = body || document.documentElement;
+	testElementParent.insertBefore( testElement, testElementParent.firstChild );
+
+	div.style.cssText = "position: absolute; left: 10.7432222px; top: 10.432325px; height: 30px; width: 201px;";
+
+	offset = $( div ).offset( function( _, offset ) {
+		return offset;
+	}).offset();
+
+	testElement.innerHTML = "";
+	testElementParent.removeChild( testElement );
+
+	offsetTotal = offset.top + offset.left + ( body ? 2000 : 0 );
+	support.fractions = offsetTotal > 21 && offsetTotal < 22;
+})();
+
 }( jQuery ));