Advanced Networking: Prediction & Authority (Blueprint)

What/Why: Build responsive multiplayer with client-side prediction, lag compensation, and authoritative server validation for AAA-quality networking.

Prereqs

• Understanding of Has Authority vs Is Locally Controlled
• Network profiling tools: stat net, Network Emulation settings

Steps

1. Client-Side Prediction Pattern

• Input Component: store inputs locally, send to server via RPC with timestamp
• Movement Component: apply movement immediately on owning client
• Server validates and corrects; clients reconcile on authority mismatch
• Use Smooth Client Position for visual correction without snapping

2. Lag Compensation for Hit Registration

• Server stores player positions per tick in circular buffer (last 1 second)
• On hit RPC from client: rewind server state to client's perceived time
• Validate hit against rewound positions, apply damage if valid
• Use GetWorld()->GetTimeSeconds() and client RTT for rewind calculation

3. Authoritative Server Validation

• Server RPCs: validate all gameplay actions (jump height, ability cooldowns, item usage)
• Client optimization: show immediate feedback, roll back on server rejection
• Use Gameplay Tags for validation: server checks CanUseAbility tags before execution

4. Network Compression Patterns

• Quantize movement vectors: FVector_NetQuantize10 for positions, FVector_NetQuantizeNormal for directions
• Pack boolean flags into bit fields using UPROPERTY(Meta = (Bitmask))
• Use RepNotifyCondition = REPNOTIFY_OnChanged to avoid redundant updates

5. Large-Scale Optimization

• Network Culling: override IsNetRelevantFor() based on distance and line of sight
• Update Frequency scaling: reduce NetUpdateFrequency for distant/occluded actors
• Batch small updates: collect per-tick changes, send as single RPC every 0.1s

6. Seamless World Travel

• Persistent player data via GameInstanceSubsystem
• Server transition: save player state, load new level, restore state
• Client loading screens: use OpenLevel with seamless travel options

Data

• DA_NetworkSettings: RTT thresholds, update frequencies, culling distances
• Client input buffer size and reconciliation tolerance settings

Networking

• Critical: all gameplay-affecting actions must be server-authoritative
• Optimization: predictive UI updates with server correction fallback

Performance

• Target: <100ms perceived input delay with 50ms+ RTT
• Server tick budget: 5-10ms for 20-tick dedicated server
• Memory: limit position history to 1-2 seconds (20-40 entries at 20Hz)

Testing

• Network Emulation: test with 100ms RTT, 5% packet loss
• Stress test: 50+ players with prediction and reconciliation active
• Edge cases: validate hit registration accuracy under high latency

Suggested prompts

• "UE 5.6 Blueprints only. Implement client-side movement prediction with server reconciliation using smooth correction."
• "Show lag compensation for hit registration: client sends hit RPC, server rewinds state and validates."
• "Create network culling system that reduces update frequency for distant players dynamically."
• "Provide authoritative validation pattern for abilities with client prediction and rollback."

Prompts for this example

• "Write Blueprint RPC nodes for client input submission with timestamp and server validation with correction."
• "Show position buffer management for lag compensation: store, rewind, validate hit against historical positions."