[gnome-shell] Clean up definition of dragOffsetX, dragOffsetY

[Colin Walters <walters src gnome org>]

commit aa7de264e683216e560b870ff43743aefaaeda54
Author: Colin Walters <walters verbum org>
Date:   Fri Mar 5 15:23:42 2010 -0500

    Clean up definition of dragOffsetX, dragOffsetY
    
    These variables were computed strangely; through cancellation
    they'd end up being negative 1/2 the width/height of the actor,
    so just use that directly.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=607821

 js/ui/dnd.js |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/js/ui/dnd.js b/js/ui/dnd.js
index 9188cad..e3596d3 100644
--- a/js/ui/dnd.js
+++ b/js/ui/dnd.js
@@ -170,8 +170,8 @@ _Draggable.prototype = {
             }
             this._dragOrigParent = undefined;
 
-            this._dragOffsetX = this._dragActor.x - this._dragStartX;
-            this._dragOffsetY = this._dragActor.y - this._dragStartY;
+            this._dragOffsetX = - this._dragActorSource.width / 2;
+            this._dragOffsetY = - this._dragActorSource.height / 2;
         } else {
             this._dragActor = this.actor;
             this._dragActorSource = undefined;
@@ -181,8 +181,8 @@ _Draggable.prototype = {
             this._dragOrigScale = this._dragActor.scale_x;
 
             let [actorStageX, actorStageY] = this.actor.get_transformed_position();
-            this._dragOffsetX = actorStageX - this._dragStartX;
-            this._dragOffsetY = actorStageY - this._dragStartY;
+            this._dragOffsetX = actorStageX - stageX;
+            this._dragOffsetY = actorStageY - stageY;
 
             // Set the actor's scale such that it will keep the same
             // transformed size when it's reparented to the stage