Desync Detection

Currently, the game does not verify clients simulation results. So if the clients simulation diverged, their simulation would only get further apart from the frame the desync started.

The FrameSyncEngine hashes the FrameSyncBehaviour data once every 60 FrameSync frames. The FrameSync server will verify the clients checksums and notify the clients which have different simulation results from others.

In this game, the only stateful component managed by the FrameSyncBehaviour is the SoccerGameFlow component. You have implemented the IFrameSyncDataContainer interface to export its states so the player scores and timerId are being verified.

You also created the SoccerPhysicsSnapshot to take snapshots of the physics engine. To verify the physics states stay in sync, you can override the OnFrameSyncGetExternalChecksum() method in the SoccerFrameSyncEngineController.

Add the highlighted code to the SoccerFrameSyncEngineController. You are going to verify the positions of the Ball and the Cars using the FrameSyncChecksum API. Also, you are going to stop the FrameSyncEngine on desync.

Drag the ball and the cars to the checksum fields in the inspector.

C#

using SocketWeaver.FrameSync;
using SocketWeaver.FPhysics3D;
using SocketWeaver.FixedMath;
using UnityEngine;

namespace SWExample.Soccer
{
    public class SoccerFrameSyncEngineController : FrameSyncEngineController
    {
        public FPhysics3DManager physicsEngine;

        [Header("checksum")]
        public FTransform ball;
        public FTransform player1;
        public FTransform player2;

        protected override void OnFrameSyncCollectPlayerInput(FrameSyncEngine frameSyncEngine, FrameSyncGame game)
        {
            if (engineMode == EngineMode.Offline)
            {
                FrameSyncPlayer player1 = game.GetPlayer(1);

                player1.SetInputX((FFloat)Input.GetAxis("Horizontal"));
                player1.SetInputY((FFloat)Input.GetAxis("Vertical"));
            }
            else
            {
                frameSyncEngine.game.localPlayer.SetInputX((FFloat)Input.GetAxis("Horizontal"));
                frameSyncEngine.game.localPlayer.SetInputY((FFloat)Input.GetAxis("Vertical"));
            }
        }

        protected override void OnStart()
        {
            physicsEngine.Initialize();
        }

        protected override void OnFrameSyncFinishedSimulationForCurrentFrame(int frameNumber)
        {
            physicsEngine.OnUpdate(FrameSyncTime.fixedDeltaTime);
        }

        protected override IFrameSyncSnapshot OnFrameSyncCreateCustomSnapshot(int frameNumber)
        {
            return new PhysicsSnapshot(frameNumber);
        }

        protected override IFrameSyncSnapshot OnFrameSyncImportCustomSnapshot(int frameNumber, byte[] bytes)
        {
            return new PhysicsSnapshot(frameNumber, bytes);
        }

        protected override uint OnFrameSyncGetCustomHashCode()
        {
            using (FrameSyncChecksum checksum = FrameSyncChecksum.Instance)
            {
                //If velocities are out of sync,
                //Positions should be out of sync as well. 
                //So we are only verifying positions. 
                checksum.Add(ball.position);
                checksum.Add(player1.position);
                checksum.Add(player2.position);

                return checksum.value;
            }
        }

        protected override FrameSyncRestoreMethod OnFrameSyncDesyncDetected(FrameSyncDesyncInfo desyncInfo)
        {
            Debug.LogError("Desync!");
            return FrameSyncRestoreMethod.Abort;
        }
    }
}