synchronization-algorithms_skill

Overview

This skill explains practical synchronization algorithms for responsive multiplayer games, covering client prediction, interpolation, rollback netcode, and lockstep. It summarizes how each technique affects responsiveness, visual smoothness, and determinism, and provides guidance for choosing and tuning approaches by genre and latency budget. The content focuses on concrete implementation patterns and troubleshooting tips for desyncs and visible artifacts.

How this skill works

The skill describes what each technique inspects and does: client prediction runs inputs locally and later reconciles with server state using a prediction buffer; interpolation renders other entities by blending between buffered states to hide jitter; rollback netcode snapshots state and re-simulates frames when opponent inputs differ; lockstep exchanges only inputs and requires deterministic simulation. It highlights when to store snapshots, how to reapply inputs, and how to smooth corrections to avoid visual popping.

When to use it

• Use client prediction for fast-action games (FPS, action) where low input latency is critical.
• Use interpolation for rendering other players and NPCs to smooth network jitter.
• Use rollback netcode for precise, timing-sensitive genres like fighting games.
• Use lockstep for RTS or turn-based games where determinism and minimal bandwidth matter.
• Combine techniques (e.g., prediction + interpolation) for MMOs or racing games with mixed needs.

Best practices

• Keep a circular prediction buffer with tick-indexing and tolerance checks to reconcile safely.
• Render behind real time with a small interpolation buffer (typical 100–200 ms) to trade latency for smoothness.
• When reconciling, reapply stored inputs and smooth corrections (lerp or damping) instead of snapping.
• For rollback, limit max rollback frames (7–8 frames at 60 fps) and optionally add 0–3 frame input delay.
• Ensure determinism for lockstep: fixed-point math, synced RNG seeds, identical execution order, and periodic hash checks.

Example use cases

• Implement a prediction buffer that stores input and predicted state per tick and reconciles on server update.
• Buffer incoming remote player states and interpolate between two most recent states to render smooth motion.
• Snapshot full game state each frame in a fighting game and rollback+resimulate on input mismatch.
• Design an RTS input-exchange loop where clients wait for all player inputs and then execute deterministically.
• Tune interpolation buffer size to reduce rubber-banding without making gameplay feel laggy.