Don't clobber mouse offset properties if we don't adjust them

Fixes jquery#165

Author: dmethvin

jquery.mousewheel.js

@@ -99,9 +99,7 @@
             delta      = 0,
             deltaX     = 0,
             deltaY     = 0,
-            absDelta   = 0,
-            offsetX    = 0,
-            offsetY    = 0;
+            absDelta   = 0;
         event = $.event.fix( orgEvent );
         event.type = "mousewheel";
 
@@ -191,16 +189,14 @@
         // Normalise offsetX and offsetY properties
         if ( special.settings.normalizeOffset && this.getBoundingClientRect ) {
             var boundingRect = this.getBoundingClientRect();
-            offsetX = event.clientX - boundingRect.left;
-            offsetY = event.clientY - boundingRect.top;
+            event.offsetX = event.clientX - boundingRect.left;
+            event.offsetY = event.clientY - boundingRect.top;
         }
 
         // Add information to the event object
         event.deltaX = deltaX;
         event.deltaY = deltaY;
         event.deltaFactor = lowestDelta;
-        event.offsetX = offsetX;
-        event.offsetY = offsetY;
 
         // Go ahead and set deltaMode to 0 since we converted to pixels
         // Although this is a little odd since we overwrite the deltaX/Y

jquery.mousewheel.min.js

@@ -59,3 +59,29 @@ QUnit.test( "natively triggered events", function( assert ) {
 
     markup.remove();
 } );
+
+QUnit.test( "mouse event properties are passed through", function( assert ) {
+	assert.expect( 4 );
+
+    var markup = jQuery( "<p>wheelme</p>" ).appendTo( "body" );
+
+    markup.on( "mousewheel", function( e ) {
+        var org = e.originalEvent;
+        assert.equal( org.clientX, 342, "original event has clientX: " + org.clientX );
+        assert.equal( org.clientY, 301, "original event has clientY: " + org.clientY );
+        assert.ok( e.offsetX < org.clientX, "got plausible offsetX in the event: " + e.offsetX );
+        assert.ok( e.offsetY < org.clientY, "got plausible offsetY in the event: " + e.offsetY );
+    } );
+
+    // Not sure why this property is manipulating offsetX/Y but the behavior cannot
+    // change in a minor version so it will stay since it's set to true right now.
+    // For testing we just want to ensure that the properties get through.
+    var event1 = makeWheelEvent( 0, 2.2 );
+    event1.offsetX = 1;
+    event1.offsetY = 2;
+    event1.clientX = 342;
+    event1.clientY = 301;
+    markup[ 0 ].dispatchEvent( event1 );
+
+    markup.remove();
+} );