Account for getBoundingClientRect returning read-only elements.

examples/js/controls/TrackballControls.js

@@ -85,11 +85,13 @@ THREE.TrackballControls = function ( object, domElement ) {
 
 		} else {
 
-			this.screen = this.domElement.getBoundingClientRect();
+			var box = this.domElement.getBoundingClientRect();
 			// adjustments come from similar code in the jquery offset() function
-			var d = this.domElement.ownerDocument.documentElement
-			this.screen.left += window.pageXOffset - d.clientLeft
-			this.screen.top += window.pageYOffset - d.clientTop
+			var d = this.domElement.ownerDocument.documentElement;
+			this.screen.left = box.left + window.pageXOffset - d.clientLeft;
+			this.screen.top = box.top + window.pageYOffset - d.clientTop;
+			this.screen.width = box.width;
+			this.screen.height = box.height;
 
 		}