only set this.controls.userHeight if device has positional tracking (…

…refs #3051)

src/components/look-controls.js

@@ -1,8 +1,11 @@
 var registerComponent = require('../core/component').registerComponent;
 var THREE = require('../lib/three');
+var utils = require('../utils/');
 var DEFAULT_CAMERA_HEIGHT = require('../constants').DEFAULT_CAMERA_HEIGHT;
 var bind = require('../utils/bind');
 
+var checkHasPositionalTracking = utils.device.checkHasPositionalTracking;
+
 // To avoid recalculation at every mouse movement tick
 var GRABBING_CLASS = 'a-grabbing';
 var PI_2 = Math.PI / 2;
@@ -56,9 +59,12 @@ module.exports.Component = registerComponent('look-controls', {
 
   tick: function (t) {
     var data = this.data;
+    var hasPositionalTracking = this.hasPositionalTracking !== undefined ? this.hasPositionalTracking : checkHasPositionalTracking();
     if (!data.enabled) { return; }
     this.controls.standing = data.standing;
-    this.controls.userHeight = this.getUserHeight();
+    if (hasPositionalTracking) {
+      this.controls.userHeight = this.getUserHeight();
+    }
     this.controls.update();
     this.updateOrientation();
     this.updatePosition();