Developing Multiplayer Games in Godot

What It Covers

Renee Haberman (Bip n Bits) and Chris Raidenor (KAR Games) detail the technical and design challenges of retrofitting online multiplayer into Domekeeper, a Godot-built roguelike tower defense game, covering network architecture decisions, bandwidth optimization, physics synchronization, and the economics of peer-to-peer versus dedicated server infrastructure.

Key Questions Answered

• •Physics determinism constraint: Non-deterministic physics in Godot forces a host-authoritative model where one machine simulates all physics objects and broadcasts results to every client. In Domekeeper, carried resources are physics objects, meaning with 8 players each carrying 4 resources, the host must continuously transmit data for 32 objects simultaneously, creating a hard practical player cap.
• •Bandwidth optimization via bit-packing: Naive resource synchronization sends full data structures per frame. Domekeeper's team reduced each resource packet to two 64-bit integers by encoding position, rotation, and carrier identity at the individual bit level — using 6-bit integers where full integers are unnecessary. This compression made 8-player sessions viable without requiring dedicated server infrastructure.
• •Client-trust model for indie multiplayer: Implementing server-authoritative anti-cheat requires dedicated servers, ballooning costs for premium indie games. Domekeeper deliberately trusts client-reported hit detection, accepting occasional inconsistency. This decision only works because the game uses friends-only lobbies with no public matchmaking, eliminating the adversarial player dynamic that makes server authority necessary.
• •Monster synchronization via seeded RNG: Rather than syncing monster positions every frame, Domekeeper sends a unique ID with each monster spawn, which seeds an identical random number generator on every client. Monster behavior becomes locally deterministic from spawn, requiring only event-based correction packets when clients drift out of sync, dramatically reducing per-frame bandwidth requirements for combat phases.
• •Network state manager per client: Godot's high-level networking requires scene tree objects to exist on all clients before RPCs can target them, surfacing race conditions that naive packet broadcasting hides. Domekeeper implements a per-client network state tracker so systems only transmit packets to clients in the correct loading or spawning state, preventing the ordering bugs that multiplayer introduces into single-player code.