This operation evaluates selected Streamable Cells for a given LOD Group by examining the number of child objects on each Asset Chunk (if using Multi-Chunking) creating/destroying/rebalancing Asset Chunks (again, if using Multi-Chunking), and determining if Cells should be disabled and their Assets destroyed (if the Asset Chunks of the Cells are non existent or empty and the Auto Disable and/or Auto Destroy setting are enabled).
This operation can be performed manually using the E* button or can be performed automatically as a result of another advanced operation being performed.
When performing a manual Evaluation Operation, all Asset Chunks for all selected Cells will be loaded into the Editor. This can result in major issues if too many Asset Chunks are loaded, and can even crash the Editor. As such, you should be cautious about selecting too many Cells, especially if the LOD you are evaluating is using Multi-Chunking.
When the operation is performed automatically as a result of another operation, the selected Cells will only come into play if that other operation makes use of them; otherwise, all Cells affected by the operation will be evaluated, regardless of whether they were selected.
The Evaluation Operation loads all Asset Chunks for a specific LOD belonging to a Cell and counts the number of child objects on those Asset Chunks (if Asset Chunks from a different LOD are currently loaded, they will be unloaded). If the LOD uses multi-chunking, it then rebalances the Cell to ensure that each Asset Chunk on the Cell has close to an equal number of child objects without exceeding a dev-set value (the Max Children/Chunk value set for the LOD on the World Designer Tool).
As a result of this rebalancing, it's possible that the World Designer tool determines that some Asset Chunks are no longer needed, or that new Asset Chunks are required. For the former, it has the Asset Manager in use by the LOD destroy the Asset Chunks; for the latter, the Asset Creator assigned to the LOD is called on.
If using a very large Streamable Grid (with a large number of Cells), you may be restricted to using a pre-set number of Asset Chunks per Cell when using Multi-Chunking. In these cases, Asset Chunks are not created or destroyed. Instead, the number of children on each Asset Chunk are rebalanced to be roughly equal, and no limit is placed on the maximum number of children per Asset Chunk.
When the Evaluation Operation determines that no children exists across all Asset Chunks, all but the first Asset Chunk are destroyed. This ensures that the Cell still has a valid Asset Chunk for the current LOD, in instances where the Cell remains Enabled.
When this option is enabled for the World Grouping, and the Evaluation Operation leaves behind a single Asset Chunk with no children, an additional check is performed. This check examines all Asset Chunks belonging to the Cell across all LODs (including the LOD that the Evaluation Operation was performed for), and if they are all Empty, it automatically disables the Cell on the Streamable Grid.
By default, all Asset Manager's implement logic that says an Empty Asset Chunk is one with 0 children and no Components other than the standard Transform component. You can change this behavior by overriding the IsAssetChunkEmpty method in a custom Asset Manager, and in fact, you must do this if working with non-game object Asset Chunks, as the default logic assumes the Asset Chunks are game objects.
When this option along with Auto Disable are enabled for the World Grouping, and the Evaluation Operation has determined that a Cell can be disabled, the World Designer Tool will automatically have the Asset Manager for each LOD destroy all Asset Chunks belonging to the Cell, across all LODs.
Disabling this option is not recommended, as it can result in Asset Chunks being left behind in the Project for Disabled Cells. When dealing with large Streamable Grids with many Asset Chunks, finding these left behind Asset Chunks can be difficult if done at a later time.