Hey Ervin, great questions—building a 2D multiplayer/singleplayer game in Unity is a fun project, let's tackle each of your points clearly:

To get your game off the ground, you'll need these foundational pieces in place:

• Solid Unity Basics: You should be comfortable with core Unity workflows—scene building, C# scripting (Unity’s primary language), 2D rendering pipelines, and UI systems. Even multiplayer games rely on a working singleplayer core first.
• Network Programming Fundamentals: Understand TCP vs. UDP differences, core client-server concepts like connection handshakes, data synchronization models (state sync vs. frame sync), and basic networking terms (IP addresses, ports). Without this, writing network logic will feel like shooting in the dark.
• Stable Unity LTS Version: Stick to a Long-Term Support release like 2021 LTS or 2022 LTS. These versions have mature networking APIs and fewer bugs compared to beta builds—critical for avoiding unexpected mid-development issues.
• Proper Development Environment: Ensure your machine has a stable internet connection (for multiplayer testing), and if testing local LAN play, make sure all devices are on the same network. A lightweight text editor for log checking can also complement Unity’s built-in Console.
• Clear Requirements Outline: Define your core gameplay first—Is it turn-based or real-time? Will singleplayer mode reuse multiplayer server logic, or be entirely local? These decisions shape your architecture, so don’t skip this step.

Unity’s server-client model centers on authoritative vs. non-authoritative endpoints, where either a Host (acting as both server and client) or dedicated Server holds the "source of truth" for game state. Here’s a breakdown:

• Host Startup: When launching as a Host, Unity spins up two instances: a local client (for the host player’s input and rendering) and a server that listens on a specified port for incoming Client connections. The local client communicates directly with the local server.
• Client Connection Flow: A Client initiates a connection by sending a request to the Host/Server’s IP and port. After server validation, a connection is established. From there, all Client inputs (movement, button presses) are sent to the server, which processes them and broadcasts updated game state (player positions, health, etc.) to all connected Clients.
• Data Synchronization Methods: Unity supports two primary sync approaches:
  • State Sync: The server periodically sends key game object states (position, health, etc.) to Clients, which update their local objects accordingly. Ideal for turn-based games or those with low real-time demands.
  • Frame Sync: All Clients send inputs to the server, which calculates the game state for each frame and syncs the result to every Client. Works best for fast-paced, competitive games where consistency is critical.
• Built-in Networking Tools: Unity’s current go-to is Netcode for GameObjects (Netcode), which wraps low-level TCP/UDP communication. It provides components like NetworkObject and NetworkBehaviour to mark objects/properties for synchronization, saving you from writing socket code from scratch.

Absolutely—you can skip all Unity or third-party networking packages and use C#’s built-in System.Net.Sockets namespace directly. Just be prepared to handle all low-level details yourself:

• TCP Implementation Steps:
  • Server: Create a TcpListener to listen on a port, use AcceptTcpClient() to accept incoming connections, and use NetworkStream to send/receive data.
  • Client: Create a TcpClient to connect to the server’s IP/port, then use NetworkStream to send input data and receive synchronized state from the server.
  • Critical Note: Run network operations on separate threads to avoid blocking Unity’s main thread (which causes game freezes). You’ll also need to handle data serialization/deserialization manually—converting game state (like player positions) to byte arrays for transmission, then parsing them back on the other end.
• UDP Implementation Steps:
  • Server: Use UdpClient to bind to a port, Receive() to get packets from Clients, and Send() to broadcast data to specific Clients.
  • Client: Create a UdpClient to send input data to the server and receive responses.
  • Caveat: UDP is connectionless, so you’ll need to build your own mechanisms for handling packet loss, out-of-order delivery, and duplicates (like adding sequence numbers or retransmission logic). It’s great for real-time games where speed matters more than perfect reliability.
• Key Challenges to Solve:
  • Thread Safety: Unity’s API can only be called from the main thread. Queue data received from network threads and process it in Update() or FixedUpdate() to avoid errors.
  • Cheat Prevention: The server must validate all Client inputs (e.g., checking if a player’s movement speed exceeds the allowed limit) to prevent cheating.
  • Smooth Synchronization: Implement interpolation or extrapolation on the Client side to avoid jitter when receiving state updates from the server.

While manual implementation is a great learning experience, using Unity’s official Netcode will save you tons of time and help you avoid common networking pitfalls—especially if you’re looking to ship your game quickly.

内容的提问来源于stack exchange，提问作者Ervin Dobri