Overview

ECS is a way of writing code that provides high performance by default.

Under the hood coherence is entirely ECS based but we supply the coherence Toolkit which is Mono-based to make it easier to make massive multiplayer games whatever way you want.

If you would like to use the coherence SDK without the toolkit, we would recommend you take some time to learn about ECS and DOTS (Data Orientated Tech Stack) with Unity.

ECS has three principal parts:

Entities — the entities, or things, that populate your game or program.

Components — the data associated with your entities, but organized by the data itself rather than by entity. (This difference in organization is one of the key differences between an object-oriented and a data-oriented design.)

Systems — the logic that transforms the component data from its current state to its next state— for example, a system might update the positions of all moving entities by their velocity times the time interval since the previous frame.

Here are various materials to learn:

• Unity DOTS Overview - https://unity.com/dots

• Unity ECS Documentation - https://docs.unity3d.com/Packages/com.unity.entities@0.14/manual/index.html

• Unity Learn, ECS - https://learn.unity.com/tutorial/entity-component-system

Creating a networked Entity

You want to spawn new stuff into the world. It is very similar to creating a .

You can add any networked components (from your schema or the coherence SDK) onto the requests.

There is one important thing to point out here -- the Translation component that is added to the new entity will correspond to a WorldPosition on the server. There are several types defined by coherence that behave this way, because the server often needs to know more about the purpose of the data than we do in our code (for example how to compress the data, etc.) In our C# code this information isn't very useful, so instead we get the ubiquitous Translation component from Unity:s ECS libraries there.

Destroy a networked Entity

You can only destroy entities that you own. Check if there is a Simulated component attached to the entity.

To destroy it, you just call DestroyEntity as normal:

EntityManager.DestroyEntity(goblinEntity);

It will be ignored if no Simulated component is attached.

Adding graphics and sound

As soon as you put a Simulated component on an entity it will start syncing its data over the network and create entities on the remote clients. You won't sync anything related to the rendering (or sound for that matter) though, so the game won't appear very much in sync. To fix this, you need to add components like RenderMesh, RenderBounds and LocalToWorld to the entity.

It turns out that doing it that way is unnecessarily cumbersome, since you already have methods for creating whatever kind of entities your game cares about. A better approach is to keep using those methods for setting up your entities and replace the networked entities with those ones.

Here are the recommended steps:

1. coherence replicates the networked components (without rendering, but you can see them in the Entity Debugger)

2. The game finds out that it can represent those entities visually (see below)

3. Create the visual representation and inform the server that it should update this new entity instead

Step 1 is already working if you have set up the SDK properly and have a WorldPositionQuery running.

Step 2 is more interesting. In its simplest form you need a system that looks for entities with some specific components, but are lacking RenderMesh or similar components. Here's an example:

Finally in step 3 you can instantiate a new (local) Entity with all the graphics and other things needed for it to look good. You replace the networked entity with this new, good looking one using a utility method named Replace. It tells the coherence SyncSendSystem about this new entity, copies all the components from the networked entity, and finally removes the networked one. Since the new entity has a RenderMesh now, it won't be processed by the ForEach function again and coherence will keep updating it due to it having all the necessary network components!