Part 4: Designing a Real-Time Game Server

Interpolation for remote players is a smoothing technique that makes movement of other players (not yourself) look fluid on your screen — even if their updates come in at a lower rate (e.g. 20 Hz) or irregularly due to network jitter.

🎮 Why you need it Link to heading

Without interpolation: Link to heading

Remote players would teleport between positions.
Every new packet would cause a visual snap.
Movement would look laggy or jittery.

With interpolation: Link to heading

You buffer past positions, then smoothly animate between them.
Movement appears fluid, even over lossy networks.

🧠 How it works (conceptually) Link to heading

Client stores a short history of snapshots from the server (e.g. last 100–200ms).

Every frame, it finds two snapshots: A and B — before and after the current render time.

It uses linear interpolation to calculate where the player should appear.


Vector2 Interpolate(Vector2 a, Vector2 b, float t) {
      return a * (1.0f - t) + b * t;
  }

a = position at snapshot A
b = position at snapshot B
t = how far between A and B you are (0.0–1.0)

🧭 Timeline diagram Link to heading

|-----|-----|-----|-----|-----| <== snapshots from server (e.g. every 50ms)
       ^           ^
    snapshot A   snapshot B
        ^
  interpolation point (render frame at t = 0.5)

💡 Key trick: Interpolate in the past Link to heading

You render 100–200ms behind real time so you always have two snapshots to interpolate between. This avoids having to extrapolate and guess positions.

✅ Result Link to heading

Movement is buttery smooth.
No snapping or jitter.

Combined with client prediction for local players, gives a very polished feel.

✅ Interpolation for remote players is now added! Link to heading

The client now: Link to heading

Buffers incoming snapshots with timestamps.
Renders 100ms behind real-time using Lerp().
Outputs the interpolated position each frame.

You can tweak INTERPOLATION_DELAY_MS or add velocity interpolation for even smoother motion. Let me know if you want to visualize this or integrate it into a 2D rendering engine like SDL!

I think this is a good stopping point for now. Maybe in the future I can write more about client-side prediction, lag compensation, or other multiplayer techniques.