Avoid auto-scaling artefacts in Safari on retina displays

(resulting in “traces” when dragging items)

history.txt

@@ -2382,3 +2382,7 @@ ______
 ------
 * Threads, Objects: Experimental “ForEach” primitive (hidden in dev mode)
 * GUI: Another attempt at pointing the project dialog to the cloud if signed in
+
+141205
+------
+* Morphic: Avoid auto-scaling artefacts in Safari on retina displays (resulting in “traces” when dragging items)

morphic.js

@@ -1041,7 +1041,7 @@
 /*global window, HTMLCanvasElement, getMinimumFontHeight, FileReader, Audio,
 FileList, getBlurredShadowSupport*/
 
-var morphicVersion = '2014-December-03';
+var morphicVersion = '2014-December-05';
 var modules = {}; // keep track of additional loaded modules
 var useBlurredShadows = getBlurredShadowSupport(); // check for Chrome-bug
 
@@ -1931,7 +1931,9 @@ Rectangle.prototype.round = function () {
 
 Rectangle.prototype.spread = function () {
     // round me by applying floor() to my origin and ceil() to my corner
-    return this.origin.floor().corner(this.corner.ceil());
+    // expand by 1 to be on the safe side, this eliminates rounding
+    // artefacts caused by Safari's auto-scaling on retina displays
+    return this.origin.floor().corner(this.corner.ceil()).expandBy(1);
 };
 
 Rectangle.prototype.amountToTranslateWithin = function (aRect) {