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Crowdy Unreal SDK

The Crowdy Unreal SDK is an Unreal Engine plugin that connects your game to the Crowded Kingdoms platform. It gives you a small surface you can drive from C++ or Blueprint: real-time networking for large numbers of players, voice chat, teams, channels, and avatars.

This guide describes SDK 2.24. Open Plugins/CrowdySDK/CrowdySDK.uplugin and check VersionName before you rely on a feature described here.

This guide is written for Unreal Engine 5.8 and a C++ project.

Gameplay can be driven entirely from Blueprint, but the plugin itself compiles as C++, so your project needs a C++ target. See Installation.

The two planes​

Everything the SDK replicates lives on one of two planes, and the whole guide leans on the split.

  1. The view plane (CrowdyState). Fast, client-owned state such as movement, animation, and transient effects. The client that owns an entity writes its state and everyone else sees it. Nothing here is checked by a server.
  2. The elected host is a convention. One client is elected host to coordinate the view plane. It is a helper for shared logic, not a rule enforcer.
  3. The truth plane (your server code). Server-owned gameplay state such as hit points, stats, and inventory, held by your app's code on ck-exec. Clients ask the server for it and ask the server to change it; the server decides. This is the only place a rule is enforced. The SDK reaches it from C++ through Server Logic.
  4. The planes touch in one way. A client asks the server's code for a change and is told the result. No gameplay value ever flows from the view plane into the truth plane as trusted input.

Read The Two Planes before you decide where a new piece of state belongs.

The host is a convention the SDK helps you follow, not a server that enforces rules.

Entities​

Almost everything on the view plane is an entity: an actor with a UCrowdyEntityComponent that has a shared identity (NetID) on every client, one owner, and a remote proxy everywhere else. Events (RPC calls) are aimed at entities, and replicated properties belong to them. Entities, Identity, and Ownership covers the details.

How to read this guide​

Work through it in order the first time.

  1. Start: Installation and the Quickstart.
  2. Concepts: The Two Planes, Entities, Identity, and Ownership, Sessions and Presence, The Host Is a Convention.
  3. Crowdy Studio: sign in and connect your app from inside the editor.
  4. Runtime (view plane): map profiles, entities, RPC events, Crowdy State.
  5. Server Logic (truth plane): server-owned state on ck-exec and the code that changes it, from Blueprint or C++.
  6. Services: voice chat, teams, avatars.
  7. Guides and Reference: best practices, the sample project, packaging, and lookup tables such as console variables.
Do Crowdy Studio first

Nothing on the network works until your project knows which app it belongs to. Sign in and run Config Sync before anything else.

What is next​

Add the plugin with Installation, connect your app in Crowdy Studio, then follow the Quickstart to put your player, one entity, one event, and one replicated property on screen.