Client/Server Interpolation of Movement

Unity Engine
1

Hello.

I have an authoritative server that manages multiple clients. Naturally, I would like to add movement/physics interpolation to the game (specifically right now for the players own movements).

Does anyone know of any good resources or packages from the Asset Store that make this easier? I’ve read Source Multiplayer Networking - Valve Developer Community but that’s as far as I’ve gotten so far. I would like to avoid as much work as possible since this has probably been developed thousands of times over and is not something I’m looking forward to handling myself unless it’s necessary.

Any advice?

Thanks.

2

This script helped me, add it to your network object’s inspector and then drag it to networkview’s observed property. Should work

using UnityEngine;
using System.Collections;

public class NetworkRigidbody : MonoBehaviour {
	
	public double m_InterpolationBackTime = 0.1;
	public double m_ExtrapolationLimit = 0.5;
	
	internal struct  State
	{
		internal double timestamp;
		internal Vector3 pos;
		internal Vector3 velocity;
		internal Quaternion rot;
		internal Vector3 angularVelocity;
	}
	
	// We store twenty states with "playback" information
	State[] m_BufferedState = new State[20];
	// Keep track of what slots are used
	int m_TimestampCount;
	
	void OnSerializeNetworkView(BitStream stream, NetworkMessageInfo info)
	{
		// Send data to server
		if (stream.isWriting)
		{
			Vector3 pos = rigidbody.position;
			Quaternion rot = rigidbody.rotation;
			Vector3 velocity = rigidbody.velocity;
			Vector3 angularVelocity = rigidbody.angularVelocity;

			stream.Serialize(ref pos);
			stream.Serialize(ref velocity);
			stream.Serialize(ref rot);
			stream.Serialize(ref angularVelocity);
		}
		// Read data from remote client
		else
		{
			Vector3 pos = Vector3.zero;
			Vector3 velocity = Vector3.zero;
			Quaternion rot = Quaternion.identity;
			Vector3 angularVelocity = Vector3.zero;
			stream.Serialize(ref pos);
			stream.Serialize(ref velocity);
			stream.Serialize(ref rot);
			stream.Serialize(ref angularVelocity);
			
			// Shift the buffer sideways, deleting state 20
			for (int i=m_BufferedState.Length-1;i>=1;i--)
			{
				m_BufferedState[i] = m_BufferedState[i-1];
			}
			
			// Record current state in slot 0
			State state;
			state.timestamp = info.timestamp;
			state.pos = pos;
			state.velocity = velocity;
			state.rot = rot;
			state.angularVelocity = angularVelocity;
			m_BufferedState[0] = state;
			
			// Update used slot count, however never exceed the buffer size
			// Slots aren't actually freed so this just makes sure the buffer is
			// filled up and that uninitalized slots aren't used.
			m_TimestampCount = Mathf.Min(m_TimestampCount + 1, m_BufferedState.Length);

			// Check if states are in order, if it is inconsistent you could reshuffel or 
			// drop the out-of-order state. Nothing is done here
			for (int i=0;i<m_TimestampCount-1;i++)
			{
				if (m_BufferedState[i].timestamp < m_BufferedState[i+1].timestamp)
					Debug.Log("State inconsistent");
			}	
		}
	}
	
	// We have a window of interpolationBackTime where we basically play 
	// By having interpolationBackTime the average ping, you will usually use interpolation.
	// And only if no more data arrives we will use extra polation
	void Update () {
		// This is the target playback time of the rigid body
		double interpolationTime = Network.time - m_InterpolationBackTime;
		
		// Use interpolation if the target playback time is present in the buffer
		if (m_BufferedState[0].timestamp > interpolationTime)
		{
			// Go through buffer and find correct state to play back
			for (int i=0;i<m_TimestampCount;i++)
			{
				if (m_BufferedState[i].timestamp <= interpolationTime || i == m_TimestampCount-1)
				{
					// The state one slot newer (<100ms) than the best playback state
					State rhs = m_BufferedState[Mathf.Max(i-1, 0)];
					// The best playback state (closest to 100 ms old (default time))
					State lhs = m_BufferedState[i];
					
					// Use the time between the two slots to determine if interpolation is necessary
					double length = rhs.timestamp - lhs.timestamp;
					float t = 0.0F;
					// As the time difference gets closer to 100 ms t gets closer to 1 in 
					// which case rhs is only used
					// Example:
					// Time is 10.000, so sampleTime is 9.900 
					// lhs.time is 9.910 rhs.time is 9.980 length is 0.070
					// t is 9.900 - 9.910 / 0.070 = 0.14. So it uses 14% of rhs, 86% of lhs
					if (length > 0.0001)
						t = (float)((interpolationTime - lhs.timestamp) / length);
					
					// if t=0 => lhs is used directly
					transform.localPosition = Vector3.Lerp(lhs.pos, rhs.pos, t);
					transform.localRotation = Quaternion.Slerp(lhs.rot, rhs.rot, t);
					return;
				}
			}
		}
		// Use extrapolation
		else
		{
			State latest = m_BufferedState[0];
			
			float extrapolationLength = (float)(interpolationTime - latest.timestamp);
			// Don't extrapolation for more than 500 ms, you would need to do that carefully
			if (extrapolationLength < m_ExtrapolationLimit)
			{
				float axisLength = extrapolationLength * latest.angularVelocity.magnitude * Mathf.Rad2Deg;
				Quaternion angularRotation = Quaternion.AngleAxis(axisLength, latest.angularVelocity);
				
				rigidbody.position = latest.pos + latest.velocity * extrapolationLength;
				rigidbody.rotation = angularRotation * latest.rot;
				rigidbody.velocity = latest.velocity;
				rigidbody.angularVelocity = latest.angularVelocity;
			}
		}
	}
}