coherence has several key features that makes big worlds viable. Read more about:
Creating massive multiplayer worlds
Unity has a well-known limitation of offering high precision positioning only within a few kilometers from the center of the world. A common technique to get around this limitation is to move the whole world underneath the player. This is called world origin shifting. Here's how you can use it with coherence.
To represent the absolute position of Game Objects on the Replication Server, we use the 64-bit floating-point format. This format allows for sub-1mm precision out to distances of 5 billion kilometers. To keep the implementation simple, floating origin position and any Game Object's absolute position is limited to the 32-bit float range, but because of the Floating Origin, it will have precision of a 64-bit float when networked with other Clients.
Here is a simple example how the floating origin could be used. We will create a script that is attached to the player Prefab and is active only on the Client with authority.
Calling the CoherenceBridge.TranslateFloatingOrigin will shift all CoherenceSync objects by the translated vector, but you have to shift other non-networked objects by yourself. We will create another script which takes care of this.
When your floating origin changes, the CoherenceBridge.OnFloatingOriginShifted event is invoked. It contains arguments such as the last floating origin, the new one, and the delta between them. We use the delta to shift back all non-networked game objects ourselves. Since the floating origin is Vector3 of doubles we need to use ToUnityVector3 method to convert it to Vector3 of floats.
To control what happens to your entities when you change your floating origin, you can use CoherenceSync's floatingOriginMode and floatingOriginParentedMode fields. Both are accessible from the inspector under Advanced Settings.
Available options for both fields are:
MoveWithFloatingOrigin - when you change your floating origin, the Entity is moved with it, so its relative position is the same and absolute position is shifted.
DontMoveWithFloatingOrigin - when you change your floating origin, the Entity is left behind, so its absolute position is the same and relative position is shifted.
Floating Origin Mode dictates what happens to the Entity when it is a Root Object in the scene hierarchy, and Floating Origin Parented Mode dictates what happens to it when its parented under another non-synced Game Object.
coherence allows us to use multiple Simulators to split up a large game world with many entities between them. This is called spatial load balancing.
You can see load balancing in action in this video: