Performance Issue when Google Photorealistic 3D Tiles are added first

[AnDuong249]

What happened?

I've noticed a performance issue in the viewer that depends on the loading order of 3D tilesets. When the Google Photorealistic 3D Tiles are added to the viewer.primitives collection before another tileset is added, the result is a significant drop in framerate while navigating (zooming in and out). However, if the Google Photorealistic 3D Tiles are added after the other tileset, the viewer's performance is not impacted and navigation remains smooth.

Reproduction steps

1. Open Sandcastle
2. Set viewer.scene.debugShowFramesPerSecond = true;
3. Navigate around by zooming in/out (this should be the simplest option)
4. Notice that the frame drops and small freezes in the viewer
5. Modify the sandcastle to add the buildingTileset first before the Google Photorealistic 3D Tiles
6. Notice how the performance is fine without significant frame drops when zooming in and out

Sandcastle example

https://sandcastle.cesium.com/?id=google-photorealistic-3d-tiles-with-building-insert

Environment

Browser: Google Chrome v143.0.7499.41
CesiumJS Version: 1.136.0
Operating System: MacOS Tahoe 26.1

[lukemckinstry]

Thanks @AnDuong249 for this observation. I notice the performance improvement you describe.