Tileset mixed refinement fix

CHANGES.md

@@ -29,6 +29,7 @@ Change Log
 
 ##### Fixes :wrench:
 * Fixed picking for overlapping translucent primitives. [#7039](https://github.com/AnalyticalGraphicsInc/cesium/pull/7039)
+* Fixed an issue in the 3D Tiles traversal where tilesets would render with mixed level of detail if an external tileset was visible but its root tile was not. [#7099](https://github.com/AnalyticalGraphicsInc/cesium/pull/7099)
 * Fixed an issue in the 3D Tiles traversal where external tilesets would not always traverse to their root tile. [#7035](https://github.com/AnalyticalGraphicsInc/cesium/pull/7035)
 * Fixed an issue in the 3D Tiles traversal where empty tiles would be selected instead of their nearest loaded ancestors. [#7011](https://github.com/AnalyticalGraphicsInc/cesium/pull/7011)
 * Fixed an issue where scaling near zero with an model animation could cause rendering to stop. [#6954](https://github.com/AnalyticalGraphicsInc/cesium/pull/6954)

Source/Scene/Cesium3DTilesetTraversal.js

@@ -316,6 +316,17 @@ define([
             return;
         }
 
+        var hasChildren = tile.children.length > 0;
+        if (tile.hasTilesetContent && hasChildren) {
+            // Use the root tile's visibility instead of this tile's visibility.
+            // The root tile may be culled by the children bounds optimization in which
+            // case this tile should also be culled.
+            var child = tile.children[0];
+            updateTileVisibility(tileset, child, frameState);
+            tile._visible = child._visible;
+            return;
+        }
+
         if (meetsScreenSpaceErrorEarly(tileset, tile, frameState)) {
             tile._visible = false;
             return;
@@ -324,7 +335,6 @@ define([
         // Optimization - if none of the tile's children are visible then this tile isn't visible
         var replace = tile.refine === Cesium3DTileRefine.REPLACE;
         var useOptimization = tile._optimChildrenWithinParent === Cesium3DTileOptimizationHint.USE_OPTIMIZATION;
-        var hasChildren = tile.children.length > 0;
         if (replace && useOptimization && hasChildren) {
             if (!anyChildrenVisible(tileset, tile, frameState)) {
                 ++tileset._statistics.numberOfTilesCulledWithChildrenUnion;

Specs/Scene/Cesium3DTilesetSpec.js

@@ -1216,6 +1216,23 @@ defineSuite([
             });
         });
 
+        it('does not select external tileset whose root has invisible children', function() {
+            return Cesium3DTilesTester.loadTileset(scene, tilesetOfTilesetsUrl).then(function(tileset) {
+                var center = Cartesian3.fromRadians(centerLongitude, centerLatitude, 50.0);
+                scene.camera.lookAt(center, new HeadingPitchRange(0.0, 1.57, 1.0));
+                var root = tileset.root;
+                var externalRoot = root.children[0];
+                externalRoot.refine = Cesium3DTileRefine.REPLACE;
+                scene.renderForSpecs();
+
+                expect(isSelected(tileset, root)).toBe(false);
+                expect(isSelected(tileset, externalRoot)).toBe(false);
+                expect(root._visible).toBe(false);
+                expect(externalRoot._visible).toBe(false);
+                expect(tileset.statistics.numberOfTilesCulledWithChildrenUnion).toBe(1);
+            });
+        });
+
         it('does not select visible tiles not meeting SSE with visible children', function() {
             return Cesium3DTilesTester.loadTileset(scene, tilesetReplacementWithViewerRequestVolumeUrl).then(function(tileset) {
                 var root = tileset.root;