Quicker iteration during development
When developing multiplayer experiences you will need to run multiple instances of your game in order to test properly. You also need to make sure these instances can be restarted quickly, so you can iterate quickly.
coherence does not have a built-in solution for multi-client testing, but there are several options available to you, each with their own benefits and drawbacks.
The easiest method is to simply create a new build each time you want to test anything. You can launch any number of instances of that build, and have an instance running in the Editor as well.
Benefits
Easy to distribute amongst team members.
Well-understood workflow.
Drawbacks
Long iteration time as you need to continuously make builds.
Harder to debug the executables.
ParrelSync is an open-source project which allows you to open multiple Unity Editor instances, all pointing to the same Unity project (using Symbolic links).
Benefits
Short iteration times.
Easy debug because it's possible to inspect GameObjects in multiple instances.
Drawbacks
Requires you to have multiple Unity Editors open.
Caveats
EditorPrefs are not consistently shared between Editors.
All instances of the game must have identical schemas, so you might want to ensure you are using Assets baking mode rather than Source Generator so the netcode is synced across editors automatically. If you do intend to use Source Generator, you need to remember to bake in each open Unity Editor. In that case, it might make sense to enable Bake Automatically On Enter Play Mode in coherence settings. You can change both of these from the coherence Hub > Baking, or in Project Settings > coherence.
First, install the ParrelSync package as described in the Installation Instructions.
Open ParrelSync -> Clones Manager. Create a new clone, and open it.
Continue development in the original Unity Editor. Never edit files in the clone Editors.
When you need to test, ensure the netcode is baked for all editors.
Unity has an experimental package called Multiplayer Play Mode (MPPM) available for 2023.1. As this is currently experimental, we do not officially recommend it - but it does show some promise and should be mentioned. This package allows a single Editor to run several instances of a game.
Benefits
Short iteration times.
No issues with schema incompatibility.
Drawbacks
Experimental.
Now we can build the project and try out network replication locally. This example will show you how to launch a local Replication Server and connect multiple instances of the game to it.
You can run a local Replication Server from:
coherence > Local Replication Server > Run for Rooms / Run for Worlds
As with most features found in the menu, you can find local Replication Server functionality in the coherence Hub as well.
Open the Replication Servers tab and run a Room or a World Replication Server:
Regardless of how you launch it, a new terminal window will open and display the running Replication Server:
Whether you run one for Rooms or for Worlds depends on which setup you plan to use, which in turn requires the correct corresponding Sample UI.
Now it's time to make a standalone build and test network replication.
#protip: Go to Project Settings, Player and change the Fullscreen Mode to Windowed and enable Resizable Window. This will make it much easier to observe standalone builds side-by-side when testing networking.
Open the Build Settings window (File > Build Settings). Click on Add Open Scenes to add the current scene to the build.
Click Build and Run.
Select a folder (e.g. Builds) and click OK.
When the build is done, start another instance of the executable (or run the project in Unity by just hitting Play).
Click Connect in the connection UIs on both clients. Now, try focusing on one and using WASD keys. You will see the box move on the other side as well.
Congratulations! You've made your first coherence replicated experience. But this is only the beginning. Keep exploring the documentation to take advantage of more advanced coherence features.
