Rework external tiles.json

Source/Scene/Cesium3DTile.js

@@ -23,8 +23,7 @@ define([
         './Empty3DTileContentProvider',
         './PerInstanceColorAppearance',
         './Primitive',
-        './TileBoundingBox',
-        './Tileset3DTileContentProvider'
+        './TileBoundingBox'
     ], function(
         BoxOutlineGeometry,
         Cartesian3,
@@ -49,8 +48,7 @@ define([
         Empty3DTileContentProvider,
         PerInstanceColorAppearance,
         Primitive,
-        TileBoundingBox,
-        Tileset3DTileContentProvider) {
+        TileBoundingBox) {
     "use strict";
 
     /**
@@ -123,13 +121,22 @@ define([
          */
         this.numberOfChildrenWithoutContent = defined(header.children) ? header.children.length : 0;
 
+        this._numberOfUnrefinableChildren = this.numberOfChildrenWithoutContent;
+
         /**
          * DOC_TBA
          *
          * @readonly
          */
         this.hasTilesetContent = false;
 
+        /**
+         * DOC_TBA
+         *
+         * @readonly
+         */
+        this.hasContent = true;
+
         /**
          * DOC_TBA
          *
@@ -147,17 +154,35 @@ define([
 
             if (type === 'json') {
                 this.hasTilesetContent = true;
-                content = new Tileset3DTileContentProvider();
-            } else if (defined(contentFactory)) {
+                this.hasContent = false;
+                this._numberOfUnrefinableChildren = 1;
+            }
+
+            if (defined(contentFactory)) {
                 content = contentFactory(tileset, this, url);
             } else {
                 throw new DeveloperError('Unknown tile content type, ' + type + ', for ' + url);
             }
         } else {
             content = new Empty3DTileContentProvider();
+            this.hasContent = false;
         }
         this._content = content;
 
+        function setRefinable(tile) {
+            var parent = tile.parent;
+            if (defined(parent) && (tile.hasContent || tile.isRefinable())) {
+                // When a tile with content is loaded, its parent can safely refine to it without any gaps in rendering
+                // Since an empty tile doesn't have content of its own, its descendants with content need to be loaded
+                // before the parent is able to refine to it.
+                --parent._numberOfUnrefinableChildren;
+                // If the parent is empty, traverse up the tree to update ancestor tiles.
+                if (!parent.hasContent) {
+                    setRefinable(parent);
+                }
+            }
+        }
+
         var that = this;
 
         // Content enters the READY state
@@ -166,6 +191,8 @@ define([
                 --that.parent.numberOfChildrenWithoutContent;
             }
 
+            setRefinable(that);
+
             that.readyPromise.resolve(that);
         }).otherwise(function(error) {
             that.readyPromise.reject(error);
@@ -237,6 +264,13 @@ define([
         return this._content.state === Cesium3DTileContentState.READY;
     };
 
+    /**
+     * DOC_TBA
+     */
+    Cesium3DTile.prototype.isRefinable = function() {
+        return this._numberOfUnrefinableChildren === 0;
+    };
+
     /**
      * DOC_TBA
      */

Source/Scene/Cesium3DTileContentProviderFactory.js

@@ -4,13 +4,15 @@ define([
         './Composite3DTileContentProvider',
         './Empty3DTileContentProvider',
         './Instanced3DModel3DTileContentProvider',
-        './Points3DTileContentProvider'
+        './Points3DTileContentProvider',
+        './Tileset3DTileContentProvider'
     ], function(
         Batched3DModel3DTileContentProvider,
         Composite3DTileContentProvider,
         Empty3DTileContentProvider,
         Instanced3DModel3DTileContentProvider,
-        Points3DTileContentProvider) {
+        Points3DTileContentProvider,
+        Tileset3DTileContentProvider) {
     "use strict";
 
     /**
@@ -29,6 +31,9 @@ define([
         cmpt : function(tileset, tile, url) {
             // Send in the factory in order to avoid a cyclical dependency
             return new Composite3DTileContentProvider(tileset, tile, url, Cesium3DTileContentProviderFactory);
+        },
+        json : function(tileset, tile, url) {
+            return new Tileset3DTileContentProvider(tileset, tile, url);
         }
     };