Update Sandcastle demo to not trigger infinite loop

Author: lilleyse

Apps/Sandcastle/gallery/Clamp to 3D Model.html

@@ -35,7 +35,8 @@
     shadows : true,
     shouldAnimate : true
 });
-viewer.scene.globe.depthTestAgainstTerrain = true;
+var scene = viewer.scene;
+scene.globe.depthTestAgainstTerrain = true;
 
 var longitude = -2.1480545852753163;
 var latitude = 0.7688240036937101;
@@ -49,8 +50,9 @@
     }
 });
 
+viewer.trackedEntity = entity;
+
 var point = viewer.entities.add({
-    position : new Cesium.CallbackProperty(updatePosition, false),
     point : {
         pixelSize : 10,
         color : Cesium.Color.YELLOW,
@@ -70,12 +72,18 @@
 var objectsToExclude = [point];
 var cartographic = new Cesium.Cartographic();
 
-function updatePosition(time, result) {
+if (scene.sampleHeightSupported) {
+    scene.postRender.addEventListener(updatePosition);
+} else {
+    console.log('This browser does not support sampleHeight.');
+}
+
+function updatePosition(scene, time) {
     var offset = (time.secondsOfDay % duration) / duration;
     cartographic.longitude = longitude - range + offset * range * 2.0;
     cartographic.latitude = latitude;
 
-    var height = viewer.scene.sampleHeight(cartographic, objectsToExclude);
+    var height = scene.sampleHeight(cartographic, objectsToExclude);
 
     if (Cesium.defined(height)) {
         cartographic.height = height;
@@ -86,9 +94,8 @@
         point.label.show = false;
     }
 
-    return Cesium.Cartographic.toCartesian(cartographic, Cesium.Ellipsoid.WGS84, result);
+    point.position = Cesium.Cartographic.toCartesian(cartographic, Cesium.Ellipsoid.WGS84);
 }
-viewer.trackedEntity = entity;
 //Sandcastle_End
     Sandcastle.finishedLoading();
 }