Only manage the tile queue if it is not empty and improve comment

src/ol/map.js

@@ -574,10 +574,21 @@ ol.Map.prototype.handleMapBrowserEvent = function(mapBrowserEvent) {
  */
 ol.Map.prototype.handlePostRender = function() {
 
-  // Limit the number of tile loads if animating or interacting.
+  var frameState = this.frameState_;
+
+  // Manage the tile queue
+  // Image loads are expensive and a limited resource, so try to use them
+  // efficiently:
+  // * When the view is static we allow a large number of parallel tile loads
+  //   to complete the frame as quickly as possible.
+  // * When animating or interacting, image loads can cause janks, so we reduce
+  //   the maximum number of loads per frame and limit the number of parallel
+  //   tile loads to remain reactive to view changes and to reduce the chance of
+  //   loading tiles that will quickly disappear from view.
+  var tileQueue = this.tileQueue_;
+  if (!tileQueue.isEmpty()) {
     var maxTotalLoading = 16;
     var maxNewLoads = maxTotalLoading;
-  var frameState = this.frameState_;
     if (!goog.isNull(frameState)) {
       var hints = frameState.viewHints;
       if (hints[ol.ViewHint.ANIMATING] || hints[ol.ViewHint.INTERACTING]) {
@@ -585,16 +596,16 @@ ol.Map.prototype.handlePostRender = function() {
         maxNewLoads = 2;
       }
     }
-
+    if (tileQueue.getTilesLoading() < maxTotalLoading) {
-  if (this.tileQueue_.getTilesLoading() < maxTotalLoading) {
+      tileQueue.reprioritize(); // FIXME only call if view has changed
-    this.tileQueue_.reprioritize(); // FIXME only call if view has changed
+      tileQueue.loadMoreTiles(maxTotalLoading, maxNewLoads);
-    this.tileQueue_.loadMoreTiles(maxTotalLoading, maxNewLoads);
+    }
   }
 
   var postRenderFunctions = this.postRenderFunctions_;
   var i;
   for (i = 0; i < postRenderFunctions.length; ++i) {
-    postRenderFunctions[i](this, this.frameState_);
+    postRenderFunctions[i](this, frameState);
   }
   postRenderFunctions.length = 0;
 };