only calculate tile positions when necessary

src/tiledimage.js

@@ -298,19 +298,25 @@ $.extend($.TiledImage.prototype, $.EventSource.prototype, /** @lends OpenSeadrag
     /**
      * Updates the TiledImage's bounds, animating if needed. Based on the new
      * bounds, updates the levels and tiles to be drawn into the viewport.
+     * @param viewportChanged Whether the viewport changed meaning tiles need to be updated.
      * @returns {Boolean} Whether the TiledImage needs to be drawn.
      */
-    update: function() {
+    update: function(viewportChanged) {
-        var xUpdated = this._xSpring.update();
+        let xUpdated = this._xSpring.update();
-        var yUpdated = this._ySpring.update();
+        let yUpdated = this._ySpring.update();
-        var scaleUpdated = this._scaleSpring.update();
+        let scaleUpdated = this._scaleSpring.update();
-        var degreesUpdated = this._degreesSpring.update();
+        let degreesUpdated = this._degreesSpring.update();
 
+        let updated = (xUpdated || yUpdated || scaleUpdated || degreesUpdated);
+
+        if (updated || viewportChanged || !this._fullyLoaded){
             let fullyLoadedFlag = this._updateLevelsForViewport();
             this._updateTilesInViewport();
             this._setFullyLoaded(fullyLoadedFlag);
+        }
 
-        if (xUpdated || yUpdated || scaleUpdated || degreesUpdated) {
+
+        if (updated) {
             this._updateForScale();
             this._raiseBoundsChange();
             this._needsDraw = true;

src/viewer.js

@@ -3749,7 +3749,7 @@ function updateOnce( viewer ) {
 
 
     var viewportChange = viewer.viewport.update();
-    var animated = viewer.world.update() || viewportChange;
+    var animated = viewer.world.update(viewportChange) || viewportChange;
 
     if (viewportChange) {
         /**

src/world.js

@@ -243,10 +243,10 @@ $.extend( $.World.prototype, $.EventSource.prototype, /** @lends OpenSeadragon.W
     /**
      * Updates (i.e. animates bounds of) all items.
      */
-    update: function() {
+    update: function(viewportChanged) {
         var animated = false;
         for ( var i = 0; i < this._items.length; i++ ) {
-            animated = this._items[i].update() || animated;
+            animated = this._items[i].update(viewportChanged) || animated;
         }
 
         return animated;