The way Clients get information about the world is through LiveQueries. They are a tool to specify what part of the world a Client is interested in at each given moment: in other words, they define an area of interest. That way, the Replication Server won’t send information about everything that is going on in the Game World everywhere, at all times.
Instead, they will just get information about what’s within a certain area, kind of like moving a torch to look around in a dark cave.
Using LiveQueries is compulsory! Without at least one LiveQuery in the scene, no entities will be updated.
A LiveQuery is a cube that defines the area of interest in a particular part of the World. It is defined by its position and its extent (half the side of the cube). There can be multiple LiveQueries in a single scene.
A classic approach is to put a LiveQuery on the camera and set the extent to correspond to the far clipping plane or visibility distance.
Moving the GameObject containing the LiveQuery will also notify the Replication Server that the query for that particular Game Client has moved.
In addition to the LiveQuery, coherence also supports defining interest with tags. This is useful when you have some special objects that should always be visible regardless of their position.
To add a TagQuery, simply add it to a GameObject like any regular component.
All networked GameObjects with matching tags will now be visible to the Client. This coherence tag is not related to the Unity concept of Tags, and can be a string of any value. It can be configured in the Advanced Settings section of the CoherenceSync component.
Object tags and the tag requested by a TagQuery can be updated at any time while the application is running, either from the Unity Inspector or by setting CoherenceSync.coherenceTag and CoherenceTagQuery.coherenceTag with code.
Currently, only one single tag per GameObject and TagQuery is supported.
To include objects with different tags, you can create multiple TagQuery objects for each tag.
In the future, we plan to integrate TagQueries with LiveQueries allowing combined query restrictions, e.g., only show objects with tag "red" within an extent of 50.
Queries can also be used for cheat prevention, see Server authoritative setup for more information.
